# Group Project: Rotary Broach-- Building complete, all shipped out!



## ErichKeane (Jun 6, 2021)

Ever wanted a tool to make Hex or Square heads in a bolt head or something?  Surprise, its a $1500 tool!  BUT, not that difficult to make!

I've attached what I think we can base our plans off of, it seems like a decent design, though I think some of the dimensions are wacky/don't make sense tome.  I likely will want to spend some time trying to CAD it or something to make sure we get the dimensions right, but first we need to find ~4 members (Additionally, I'm pretty heavily into the dividing head project, so I'd like to get done with that work before I start my piece).

It looks like it is mostly lathe work, with 2 of the pieces requiring a mill, and nothing particularly large, so it should be cheap/easy to make and ship around.

Currently signed up members:
1- ErichKeane
2- GunsOfNavarone
3- ttabbal
4- T Bredehoft

Looks like we have all 4!  Just about all the parts are made, except for the broaching bits, which ErichKeane is still working on.  The rest of the parts are just awaiting assembly!

Final edit: All the parts are made and shipped!  Congrats everyone!


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## GunsOfNavarone (Jun 6, 2021)

How do you feel about amendments? Not necessary for everyone, but that appears to have a .6245" arbor, I guess I'd go .750 as that is a better fit for both my manual mill and CNC mill....HOWEVER, I could see using it on my lathe too. What makes best sense for tailstock use? I don't know, MT2?
EDIT-
Would we be making the actual bits? Do we need someone on board with a hardener?


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## ErichKeane (Jun 6, 2021)

GunsOfNavarone said:


> How do you feel about amendments? Not necessary for everyone, but that appears to have a .6245" arbor, I guess I'd go .750 as that is a better fit for both my manual mill and CNC mill....HOWEVER, I could see using it on my lathe too. What makes best sense for tailstock use? I don't know, MT2?
> EDIT-
> Would we be making the actual bits? Do we need someone on board with a hardener?



I'm totally open to amendments  

I have a lathe tailstock chuck I'd like to use it with which goes up to 5/8" (though I have a larger one, so .750 would work for me too).  That way we could use it on both the mill and lathe.  I suggested 1/2", since I know a lot of lathe chucks only go up to 1/2" and it is a common collet size, but that would depend on who else wants to participate.  I think we could probably get away with doing that 'to order' if the person doing that part is willing.

As for the bits, typically they are just ground out of HSS rod, which doesn't require hardening, just grinding!  I think we'd want to make at least a starter-one or two for everyone, since they tend to run about $100 each otherwise!  I have the surface grinder to do the sides, but the central-relief I just don't quite have yet, so I'd have to figure that part out.  I probably need some sort of die-grinder holder for my lathe to grind that part.


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## GunsOfNavarone (Jun 6, 2021)

I have watched videos on the cupped center. Easily done on a grinding wheel.


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## ErichKeane (Jun 6, 2021)

GunsOfNavarone said:


> I have watched videos on the cupped center. Easily done on a grinding wheel.


If you've got a good video, I would love to see it! I have an 8" grinder (plus I guess a 4" tool grinder I could use...).


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## T Bredehoft (Jun 6, 2021)

Shank diameter. a 3/4" boring bar holder could be used to hold it in an Aloris type tool mount. Or, half inch with a sleeve.

Where does material come from?  I'm considering joining the project.


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## Brento (Jun 6, 2021)

If i got into this project the great thing for it being a mt2 would be it could fit my tailstock and my mill. But idk if i can sign up for this one. I will be watching though as even when you come up with the drawings i may "borrow" them to make my own.


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## T Bredehoft (Jun 6, 2021)

Questions....lots of dimensions missing....what provision is made for thrust bearing surfaces? or is that the "grease"?


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## GunsOfNavarone (Jun 6, 2021)

I was wondering the same thing, however, if you have seen the AVE guy on Youtube, it did it with two divits (one off center) in a couple of pieces f steel...with a ball bearing sandwiched between the two. It's a crazy simple device, but yeah, if we could find plans that made a higher level tool, that's awesome. 
There is a British company that makes these and everyone copies those...I'll see if I can't find those plans or instructions, something.


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## GunsOfNavarone (Jun 6, 2021)

Instruction


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## GunsOfNavarone (Jun 6, 2021)

Ave's crazy version


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## bill70j (Jun 6, 2021)

GunsOfNavarone said:


> There is a British company that makes these and everyone copies those...I'll see if I can't find those plans or instructions, something.


FWIW, I made that "Hemingway" broach.  Their broach is pretty small, so I scaled up their drawings and made a tool capable of making much larger squares and hex's.  I got permission from the Hemingway guys to share the drawings.  Let me know if interested.

Also for the broach, I would suggest O-1, which you can harden with oxy-acetylene, then sharpen by grinding.


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## GunsOfNavarone (Jun 6, 2021)

@bill70j    ABSOLUTELY! Thank you!


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## ErichKeane (Jun 6, 2021)

T Bredehoft said:


> Shank diameter. a 3/4" boring bar holder could be used to hold it in an Aloris type tool mount. Or, half inch with a sleeve.
> 
> Where does material come from?  I'm considering joining the project.


In the other two group projects everyone buys the materials for the parts they are making.  The boring bar holders are dependent on the size of the tool holders (mine are 1.250 with a 1" sleeve), but I'm up for whatever size the group is.




T Bredehoft said:


> Questions....lots of dimensions missing....what provision is made for thrust bearing surfaces? or is that the "grease"?


I think this design is just grease The face of the 'broach holder' and the 'body' are the bearing surface it seems.




GunsOfNavarone said:


> I was wondering the same thing, however, if you have seen the AVE guy on Youtube, it did it with two divits (one off center) in a couple of pieces f steel...with a ball bearing sandwiched between the two. It's a crazy simple device, but yeah, if we could find plans that made a higher level tool, that's awesome.
> There is a British company that makes these and everyone copies those...I'll see if I can't find those plans or instructions, something.


I've seen a couple withe the ball-bearing in the middle, I'm definitely up for whatever designs we come up with.  That design above was just the one I found in my machining folder.


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## ErichKeane (Jun 6, 2021)

GunsOfNavarone said:


> Instruction


This is a pretty nice one!  I'd almost definitely make the tool 1/2" and scale it up for a 1/2" bit simply so we can use commercial broaches though.


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## T Bredehoft (Jun 7, 2021)

Size of final product.... I can't imagine broaching anything larger than  1/4 hex, (Allen Wrench driven). I could hold a 1" shank in my PM25 mill, but not my lathe... (10-30). 

I've yet to wrap my mind around the motion of the 'cutter.' It does rotate, driven by the piece being broached, does it pivot about it's long axis, or does it pivot on a point? Or are these two  differing processes? 

O-1 vs HSS for the cutter? So long as we have a grinder and it's operator we should use HSS, it's much better for its job than hardened O-1. Harder, too.


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## Brento (Jun 7, 2021)

Most of them i believe pivot on an axis i believe.


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## bill70j (Jun 7, 2021)

GunsOfNavarone said:


> @bill70j    ABSOLUTELY! Thank you!


Here is a photo of the Hemingway broach holder and its scaled-up companion.  Both use 1/2" shank broaches made from hardened O-1 tool steel. The larger one can make hex's for screws up to M12 and up to 1/2".




The attached drawing includes the holder body and spindle showing the two radial bearings and the single thrust bearing.

If this helps you guys in any way and you want the as-built drawings, just let me know.


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## Illinoyance (Jun 7, 2021)

I made my rotary broach a few years ago.  It resembles your design but has radial and thrust bearings.   made interchangeable shanks, 5/8 and MT2.  That allows me to use it in the lathe tailstock, the turret on the lathe, in the mill, or even maybe the drill press.


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## ErichKeane (Jun 7, 2021)

Hmm.... it would be interesting to build one around a tapered roller bearing, but sadly they tend to have a pretty massive OD for any reasonable ID.


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## ttabbal (Jun 7, 2021)

No idea how much I would use it, but it would be fun and nice to have around. I'll join in.


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## ErichKeane (Jun 7, 2021)

Ah, I actually figured out the purpose of those 10-32 screws on the original drawing!  When you are setting up a rotary broach, you need to make sure that the 'tip' of the tool when rotated has no runout.  The 1 degree angle has to be offset in some way by the tool bit being held off center the correct amount to get it back to running 'true' at the tip.

This is what the funny-business about the "Broach is switched with a dowel pin of the same length when shank is on a Vee Block tip of pin is adjusted to not wobble" bit in the upper-right of the drawing!

In the drawing in my original post, I now can "see" that the body has some sort of side-to-side offset built into it, but I don't really see it listed as a dimension.  it is MAYBE captured in the 'flange view' in the top-left of the drawing, where the mount holes are 200 thou off center, but I figured that was because it was a weird-3-view.

I'm guessing there is some math I need to do when designing this.  I really like the idea of including a thrust and axial bearing if possible, but I've personally not seen any I am a huge fan of yet.  I originally really liked the version in the OP because of how small the body is, but I guess that isn't particularly possible with an axial bearing.

Also, I see ttabbal's post, I'll add you to the OP!


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## T Bredehoft (Jun 7, 2021)

If you have room, I'd like to play, too.  I'm pretty good with a lathe, my PM25 mill is OK, but my 4" rotary table isn't the best for profiling.


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## ErichKeane (Jun 7, 2021)

T Bredehoft said:


> If you have room, I'd like to play, too.  I'm pretty good with a lathe, my PM25 mill is OK, but my 4" rotary table isn't the best for profiling.


Great! I'll count you in!

I think we're going to end up doing a decent amount of changes to the design. I think getting us onto an axial and thrust bearing is a good idea.  I found some needle-bearings, how do we feel about using some inexpensive needle bearings?  Are there any downsides we should be aware of for those?

Next, I like the idea of a 'round flange' instead of the 2 bolt flange on the original design.  I suspect that many of us are going to have trouble getting that sort of profiling done accurately enough.

For bearings, does anyone think needle bearings are a bad idea?  I found this set (and some others of the same size) that could be pretty cheap: https://www.amazon.com/dp/B082PCTQ2...aWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl&th=1

I THINK it means the 'broach holder' would have to be pretty accurately manufactured however, right?  

Alternatively I see this guy:


			https://www.amazon.com/Donepart-R12-2RS-Bearings-Lubricated-Double/dp/B07XP4RF5D/ref=sr_1_5?dchild=1&keywords=3%2F4+ID+bearing&qid=1623103141&s=industrial&sr=1-5
		


Also really inexpensive, but gets our 'body' OD up to almost 2"  So, what does everyone think?  

I'm leaning toward the 3 piece cheap thrust-bearings were the snap-ring is located on the original drawing (basically, at the back of the holder).


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## T Bredehoft (Jun 7, 2021)

Looking forward to a new experience...Thanks


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## T Bredehoft (Jun 7, 2021)

ErichKeane said:


> I found some needle-bearings, how do we feel about using some inexpensive needle bearings


If I understand the operation of the  broach, wobble is going to override the use of circumferential (axial) bearings. The driving unit is rigidly attached to the chuck and the driven unit wobbles in a known pattern to broach the hole. Axial bearing will limit this wobble to the failure of the bearings. Or conversely the driving unit is fixed by the tool post and the driven unit wobbles in the work mounted in the chuck. Or am I missing something?


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## ErichKeane (Jun 7, 2021)

T Bredehoft said:


> If I understand the operation of the  broach, wobble is going to override the use of circumferential (axial) bearings. The driving unit is rigidly attached to the chuck and the driven unit wobbles in a known pattern to broach the hole. Axial bearing will limit this wobble to the failure of the bearings. Or conversely the driving unit is fixed by the tool post and the driven unit wobbles in the work mounted in the chuck. Or am I missing something?


The wobble is introduced by the 1 degree angle in the base. The "body" and broach are supposed to remain concentric.


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## GunsOfNavarone (Jun 7, 2021)

It's a stupid simple concept, that AVE video shows just how simple it can be. Don't misunderstand, I want a beautiful, precision tool to hold in my hand (I mean that in a totally straight way) and this is where we have to mince ideas. It would be difficult to screw up, other than poor machining skills, but I'd like to complicate it enough where it has longevity.


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## GunsOfNavarone (Jun 7, 2021)

ErichKeane said:


> Great! I'll count you in!
> 
> I think we're going to end up doing a decent amount of changes to the design. I think getting us onto an axial and thrust bearing is a good idea.  I found some needle-bearings, how do we feel about using some inexpensive needle bearings?  Are there any downsides we should be aware of for those?
> 
> ...


I thin that those sets of bearings are turned the wrong way. Don't we need them axial not radial?


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## ErichKeane (Jun 7, 2021)

GunsOfNavarone said:


> I thin that those sets of bearings are turned the wrong way. Don't we need them axial not radial?


I think we need both axial and radial.  We could consider going with a tapered roller bearing to get us both (though, only in 1 direction for axially), but I think they are going to be too large.

The idea was to use those bearings up front to control riadial load, then on the 'back' use a thrust bearing [0] between the holder and the body.


[0] Something like these :https://www.amazon.com/ToToT-Bearin...cphy=9032901&hvtargid=pla-1186693713496&psc=1


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## GunsOfNavarone (Jun 7, 2021)

I like bill's finished product, but trying to imagine those plans and how it works....it's not happening. Am I the only one that can't follow those?
Can we take a simple idea and make our own? I'm decent with F360, maybe I'll dink around there, it's easier to imagine the tool if you can see it in 3d.


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## rwm (Jun 7, 2021)

ErichKeane said:


> The wobble is introduced by the 1 degree angle in the base. The "body" and broach are supposed to remain concentric.


I don't think this is correct. I don't think you can easily use axial needle bearings in this design. The base of the broach must necessarily move in a circle. The tip of the broach remains centered in the hole you are cutting. The easiest way to accomplish this is to have a single ball bearing at the base of the broach. This acts a a thrust bearing and allows rotary motion and angular motion away from the axis. 
You could only use an axial bearing if the angle of the bearing was very precisely calculated and the length of each broach was exactly the same. 
I recently made one of these using a single bearing design.









						Rotary Broach
					

I finally got around to making a rotary broach for that special project that I have not yet envisioned:    I used my Sherline tool cutter and grinder to grind the broaches out of O1 tool steel: I clamped a 1/2" bar in my 5C collet block and mounted the vise with 2.5 deg of angle as viewed from...




					www.hobby-machinist.com
				




As far as the broach goes, the hardest part is grinding the cutting edge and getting it to the correct size. To dish out the end I strongly recommend a Dremel wheel. It sounds primitive but works great. 

Robert


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## GunsOfNavarone (Jun 7, 2021)

Getting there...
.5" I.D. taper bearings


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## GunsOfNavarone (Jun 7, 2021)

rwm said:


> I don't think this is correct. I don't think you can easily use axial needle bearings in this design. The base of the broach must necessarily move in a circle. The tip of the broach remains centered in the hole you are cutting. The easiest way to accomplish this is to have a single ball bearing at the base of the broach. This acts a a thrust bearing and allows rotary motion and angular motion away from the axis.
> You could only use an axial bearing if the angle of the bearing was very precisely calculated and the length of each broach was exactly the same.
> I recently made one of these using a single bearing design.
> 
> ...


Yeah, it seems more the base the broach rides against is angled, causing an in/out movement, not side to side (off center)


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## ErichKeane (Jun 7, 2021)

GunsOfNavarone said:


> I like bill's finished product, but trying to imagine those plans and how it works....it's not happening. Am I the only one that can't follow those?
> Can we take a simple idea and make our own? I'm decent with F360, maybe I'll dink around there, it's easier to imagine the tool if you can see it in 3d.



I do as well!  But I have no idea what is going on in those plans either.  If you are decent at F360 you are better than my near-zero-experience with FreeCAD, so feel free!



rwm said:


> I don't think this is correct. I don't think you can easily use axial needle bearings in this design. The base of the broach must necessarily move in a circle. The tip of the broach remains centered in the hole you are cutting. The easiest way to accomplish this is to have a single ball bearing at the base of the broach. This acts a a thrust bearing and allows rotary motion and angular motion away from the axis.
> You could only use an axial bearing if the angle of the bearing was very precisely calculated and the length of each broach was exactly the same.
> I recently made one of these using a single bearing design.
> 
> ...



Really?  My understanding in these rotary broach situations (not the 'wobble broaches' that use the ball bearing) that the idea is that the broach itself rotates concentric to the 'body' of the tool, which is tipped at a 1 degree by its mount to the tailstock.  That way it presents only 1 side of the broach itself at any one point.  That 'point' catches inside the material, and as it 'spins' the in/out motion is caused entirely by that 1 degree angle moving it around at the slight incidence angle.

So the 'body' and the 'bit' still run concentric to each other.




GunsOfNavarone said:


> Getting there...
> .5" I.D. taper bearings


The tools I was planning are .5 ID, so I was considering we needed at least .75 ID on our bearings. That gets us to about 2" diameter body. We could probably get away with only 1 taper bearing vs 1 of each in the other case though.


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## Janderso (Jun 7, 2021)

I read every word of this thread.
You guys rock.
Please keep posting your progress.


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## GunsOfNavarone (Jun 7, 2021)

.75 bearing


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## rwm (Jun 7, 2021)

"Really? My understanding in these rotary broach situations (not the 'wobble broaches' that use the ball bearing) that the idea is that the broach itself rotates concentric to the 'body' of the tool, which is tipped at a 1 degree by its mount to the tailstock. That way it presents only 1 side of the broach itself at any one point. That 'point' catches inside the material, and as it 'spins' the in/out motion is caused entirely by that 1 degree angle moving it around at the slight incidence angle."

Yes, I think that plan can work as long as the TIP of the broach remains centered on the axis of rotation. That means that once you set the bearing angle, each tool has to have the exact same length. I have no idea how to calculate and measure that or what the tolerance is for being off angle. It looks to me like the original designer tried to measure that using a dowel pin in place of a broach? I suspect a lot of these might work due to lack of rigidity in the tooling allowing for some degree of wobble even if you can't see it.
My humble opinion is that the single bearing is much easier.
R


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## GunsOfNavarone (Jun 7, 2021)

.625 & .6875
 If you want a bit above/bit below


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## GunsOfNavarone (Jun 7, 2021)

I'm really leaning toward this design, simple bearings as well, compact design....thoughts?
YouTube Broach


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## GunsOfNavarone (Jun 7, 2021)

How to grind the cutting bits
Broach grinding


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## ErichKeane (Jun 7, 2021)

rwm said:


> "Really? My understanding in these rotary broach situations (not the 'wobble broaches' that use the ball bearing) that the idea is that the broach itself rotates concentric to the 'body' of the tool, which is tipped at a 1 degree by its mount to the tailstock. That way it presents only 1 side of the broach itself at any one point. That 'point' catches inside the material, and as it 'spins' the in/out motion is caused entirely by that 1 degree angle moving it around at the slight incidence angle."
> 
> Yes, I think that plan can work as long as the TIP of the broach remains centered on the axis of rotation. That means that once you set the bearing angle, each tool has to have the exact same length. I have no idea how to calculate and measure that or what the tolerance is for being off angle. It looks to me like the original designer tried to measure that using a dowel pin in place of a broach? I suspect a lot of these might work due to lack of rigidity in the tooling allowing for some degree of wobble even if you can't see it.
> My humble opinion is that the single bearing is much easier.
> R


Yep, that seems to be the case of all of the "rotary style" of broaches vs a wobble. As far as "a lot of these might work due to lack of rigidity", you could very well be right.



GunsOfNavarone said:


> I'm really leaning toward this design, simple bearings as well, compact design....thoughts?
> YouTube Broach


This is almost exactly what I was proposing above (and my thoughts above were heavily influenced by that!).  That one uses 2 bearings, the needle bearings near the front and a thrust-washer-bearing near the back.  Actually, he uses _3_ bearings, but I think the rear most ball bearing is perhaps superfluous: https://www.etsy.com/listing/831959563/rotary-broach-plan?ref=shop_home_active_1

You can see the plans at 21 sec of that video, and on the preview of that site.

I'd be OK having each of us spend the $13 and each making a part for that one, though I'm a touch concerned of its apparent lack of adjustability to get the dowel-pin running true.


GunsOfNavarone said:


> How to grind the cutting bits
> Broach grinding


I was actually JUST watching that a bit ago.  Sadly I didnt see the part that I most care about, getting the 'dish' in the end.


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## ErichKeane (Jun 7, 2021)

1 downside to his design is that it uses 3/8" bits instead of the 1/2" bits.  This can limit the size of what you can do, since you're limited by the size of the rod (you can BUY bigger ones, but they are expensive, and making them would require a cylinder grinder to form the shank.

A 1/2" rod limits you to a .433" across flats, 3/8 limits to .324.


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## rwm (Jun 7, 2021)

After watching that video (like 5 times!) I see how he achieves his result. His back plate introduces a 1deg angle on the broach. Then he offsets the base and indicates so the tip of the broach is centered on the axis of rotation. That should work fine. If your broach length varies, you could indicate it and adjust the offset to get centered on the hole. If all your broaches are exactly the same length you would only need to indicate it the first time.
I would love to see you guys successfully execute this!
Robert


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## ErichKeane (Jun 7, 2021)

rwm said:


> After watching that video (like 5 times!) I see how he achieves his result. His back plate introduces a 1deg angle on the broach. Then he offsets the base and indicates so the tip of the broach is centered on the axis of rotation. That should work fine. If your broach length varies, you could indicate it and adjust the offset to get centered on the hole. If all your broaches are exactly the same length you would only need to indicate it the first time.
> I would love to see you guys successfully execute this!
> Robert


Right, yes, that is exactly what the design I posted does too, except it has some adjustment for the offset.  The video only has the offset adjusted in the range of the clearance holes I think...

Purchased bits tend to be all 1.750", so I was going to try to replicate that (in case we wanted to just buy off the shelf ones), but I like the idea of being able to indicate in to adjust the cutter.


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## ErichKeane (Jun 8, 2021)

Another interesting project version we might take some cues from: 




I like that he split the mount and the body and put the angle in the body instead.  This might be a touch harder to make, but it makes mounts interchangeable.  Not sure it is worth it though for the lathe-like work on the mill...  Also, the ER collets for the mount is interesting!


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## ErichKeane (Jun 8, 2021)

Also, re-taught myself a bit of free cad today and came up with the attached.  The only annoying one is that the 'dish' in the end and the large-diameter of the hex aren't linked, so I'd need to adjust those manually together.


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## rwm (Jun 8, 2021)

I love the optical centering microscope in that video! 
Robert


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## GunsOfNavarone (Jun 8, 2021)

Yeah the centering needs to be easier and quick. I hate having to adjust a independent jaw chuck, some of these designs would be possibly worse. How do these $1000 ones work? I'm sure they are the bee's knees.


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## GunsOfNavarone (Jun 8, 2021)

@8:43....dishing the bits.
Cupping the end of bit


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## Ianagos (Jun 9, 2021)

Hmm looks like I missed this one.. let me know if you guys need any help.


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## GunsOfNavarone (Jun 9, 2021)

I guess that an issue to discuss. When I started the “this madness needs to stop” thread, the purpose was to get people to (if they haven’t much or all) to learn to work from blueprints with tight tolerances. That way a part Dave made would fit flawlessly in a part Mary made. It getting the feeling that everyone is just going to make there own broach? One person is making all of X part(s) and someone else is making Y part(s)? We probably need to work this out as it maybe a group build or a group making the same thing at roughly the same time.
Depending how this is done, there maybe plenty of room for @Ianagos or may not be.


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## ErichKeane (Jun 9, 2021)

>>One person is making all of X part(s) and someone else is making Y part(s)?

I was hoping for this, based on the purpose of the original thread   I liked this project since the parts-list was so much lower than the dividing head, but apparently we have more interest than parts  

Would there be interest in doing _2_ groups?


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## GunsOfNavarone (Jun 9, 2021)

I'm down for whatever. people taking on responsibilities that match there skill/equipment. People pushing themselves and taking on things they are weak at (to learn)
As that first thread got away from me, I went out and found what I needed. I made a 6 bolt compound clamp out of A2 tool steel. I found the plans here and rated myself on out come of measurements. Sub a thou and now my lathe has new life with higher rigidity.
I also upped my F360 game and CNC work with some complex designs (again in A2)
You gotta push yourself and get outta of the ruts...you’ll be a better “machinist” in the end.


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## Ianagos (Jun 9, 2021)

GunsOfNavarone said:


> I guess that an issue to discuss. When I started the “this madness needs to stop” thread, the purpose was to get people to (if they haven’t much or all) to learn to work from blueprints with tight tolerances. That way a part Dave made would fit flawlessly in a part Mary made. It getting the feeling that everyone is just going to make there own broach? One person is making all of X part(s) and someone else is making Y part(s)? We probably need to work this out as it maybe a group build or a group making the same thing at roughly the same time.
> Depending how this is done, there maybe plenty of room for @Ianagos or may not be.



Well I’m very familiar with working from prints no worries there.

I just like these projects as they are something different from the typical work I do. 

If there is no room for me it’s not an issue at all.


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## ErichKeane (Jun 10, 2021)

So I'm playing with that design like TomMakeHere did in the design we talked about above.  I was trying to modify it slightly to use imperial bearings (not particularly possible with the front needle bearing), but I'm also not a fan of how the body needs to be formed in order to use 2 bearings.  There is a double-flat internal dimension where the distance between the two flats its pretty critical.  It seems to me that it would be a pretty nasty dimension to hit, particularly in the sizes we're talking about.

Instead, I have 2 options:
1- I go with a longer needle bearing at the front, and count on THAT to control the 'sheering', then just the thrust bearing at the back. It is perhaps a little suceptible to radial forces as the 'back' is unsupported in that way (though ~1" of support at the front).

2- Do those (perhaps the 3/4 needle bearing still at the front), but replace the thurst bearing/normal bearing with a taper-roller bearing.  GunsOfNavarone posted above about a 1/2" one that would work fine, if a little large, resulting in a slightly larger diameter body.
I could optimally use a 3/8" ID taper roller bearing, but I couldn't find any cheap ones.

Additionally, I'd like to add 2 features, which I think I'd like to hear feedback from the builders/others!
1- Some sort of grease nipple.  TomMakesHere's version (the fluted one in the video above) looks like it requires ocassional disassembly to grease the needle bearing and thrust bearing.  He has to do this because his normal bearing on the back ends up being sealed.  Even in his design I think I could put a grease nipple on the body.

2- calibration screws: Once you've got it assembled, you have to get the offset on the 1 degree taper right-on to make sure the 'points' of your bit are all the same 'height'.  The one in the original-post uses a couple of adjustment screws to do so, TomMakesHere suggests just 'tapping' it in after loosening the bolts.  I'd love to do the adjustment screws if I could find a place for them.

So, thoughts/feedback?  Anyone have a 3/8" ID taper roller bearing I could design this around?


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## GunsOfNavarone (Jun 10, 2021)

I have never owned or used a rotary broach, so my input is shooting from the hip. It seems many I have seen are completely disassemble. If your talking about one that requires a zerk because once you build it, you're never getting back into those bearings.....I'm not a fan. The adjustment screws; I am a bit confused (though I have seen those) why it can't be made with zero offset so it doesn't need that, and rely on the base plate being made with 1* of angle to facilitate the in/out broaching action.
I guess the bearings used would be solely based on design choices, but whatever is needed. Being we are making a tool that would cost 100's of dollars, I don't mind spending 20, 30 or ? dollars on bearings. I wouldn't take anything out of the mix because the bearing seem expensive (of course I don't know what too expensive was in this case.


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## ErichKeane (Jun 10, 2021)

GunsOfNavarone said:


> I have never owned or used a rotary broach, so my input is shooting from the hip. It seems many I have seen are completely disassemble. If your talking about one that requires a zerk because once you build it, you're never getting back into those bearings.....I'm not a fan.


This would still be able to be taken apart, the point of the zerk is so you don't have to!  My plan still has the bolts-to-the-backing-plate + cir-clip construction, but it means you don't have to take those apart (and perhaps lose your calibration) in order to grease it.  A part of me suspects it is just superfluous, as we aren't going to be using these that much...



GunsOfNavarone said:


> The adjustment screws; I am a bit confused (though I have seen those) why it can't be made with zero offset so it doesn't need that, and rely on the base plate being made with 1* of angle to facilitate the in/out broaching action.


So the point of the adjustable offset is to make up for the 1 degree angle.  The idea is that as the broach-bit rotates, the cutting points need to all be the same distance from the center-of-the-machine-spindle, otherwise you cut an off center or oblong broach.  If you check out the 'troubleshooting' guide  in the 3rd image here, it explains it a bit: https://www.etsy.com/listing/831959563/rotary-broach-plan?ref=shop_home_active_1

You'll see from that guide, he shows that you can loosen the mounts and 'tap' it into alignment, though I'm not sure I'm a huge fan of that.  I always do a really terrible job trying to tap things in 




GunsOfNavarone said:


> I guess the bearings used would be solely based on design choices, but whatever is needed. Being we are making a tool that would cost 100's of dollars, I don't mind spending 20, 30 or ? dollars on bearings. I wouldn't take anything out of the mix because the bearing seem expensive (of course I don't know what too expensive was in this case.



The 3/8" bore ones i found were pretty costly, like $120 for a bearing.  I can keep looking though.


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## rwm (Jun 10, 2021)

I wonder if the best way to adjust the offset would be to loosen the screws and bring the tip of your broach up to a chamfered hole centered in the lathe chuck? 
Robert


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## ErichKeane (Jun 10, 2021)

FWIW, I just figured out the Hemingway Kits design  Stefan G's video shows a cross-section: 




I'm not a huge fan of it not being all that adjustable, and the idea of cutting a 1 degree taper inside a bore seems pretty awful (and requires a mill).  That said, it looks like it uses a thrust bearing and 2 normal bearings.  

It DOES have a good idea in that the tool-holding spindle has a bore out the back, which is super nice for knocking out the tool if you get it stuck!


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## GunsOfNavarone (Jun 10, 2021)

I did pull that video of Stephan's up a couple days ago....but then saw it was something like 4 parts....nope. I'm gonna do some poking around now, but being in my 90* shop for the last 9 hours...I am BEAT!


----------



## GunsOfNavarone (Jun 10, 2021)




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## GunsOfNavarone (Jun 10, 2021)

Been a productive last 5 mins!


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## ErichKeane (Jun 10, 2021)

GunsOfNavarone said:


> Been a productive last 5 mins!


This one here is a really nice and compact design!  Probably my favorite so far.  One thing I might think about changing on it is to do a 4-bolt circular flange for the connections, otherwise a rotary-table is required (and at least someone said they didn't have a good one).

It is another design that avoids using 2 bearings to control radial load. I suspect with the length in question it isn't that big of a deal to skip the other bearing.  That one also uses the 'tap into calibration' method.  Also it uses a bunch of those weird 'mms' all over the place


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## ErichKeane (Jun 10, 2021)

ErichKeane said:


> This one here is a really nice and compact design!  Probably my favorite so far.  One thing I might think about changing on it is to do a 4-bolt circular flange for the connections, otherwise a rotary-table is required (and at least someone said they didn't have a good one).
> 
> It is another design that avoids using 2 bearings to control radial load. I suspect with the length in question it isn't that big of a deal to skip the other bearing.  That one also uses the 'tap into calibration' method.  Also it uses a bunch of those weird 'mms' all over the place


I also don't understand the 1 mm step in the 'bearing holder' at the front, perhaps just clearance?  His bearing is 32mm, so the front one seems unnecessary.


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## ttabbal (Jun 10, 2021)

I think I would prefer a straight shank. Can hold it in a collet or drill chuck, so I could use it on the mill as well.


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## GunsOfNavarone (Jun 10, 2021)

I've never made a Morse Taper before....if I were to use it mostly on my lathe, that would be my preference. Who knows, maybe I'll want to use it on my mill, in which case, 3/4"(or smaller) straight works. I guess I'm flexible, but how would you use a 3/4" straight on a lathe? You wouldn't I suspect.


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## ErichKeane (Jun 10, 2021)

GunsOfNavarone said:


> I've never made a Morse Taper before....if I were to use it mostly on my lathe, that would be my preference. Who knows, maybe I'll want to use it on my mill, in which case, 3/4"(or smaller) straight works. I guess I'm flexible, but how would you use a 3/4" straight on a lathe? You wouldn't I suspect.


You can just use a tailstock drill chuck.


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## GunsOfNavarone (Jun 10, 2021)

Not with a 3/4"...MAYBE a half, but think about that overhang/weight. Each person could make the end that they want if it comes down to it, that's not a terribly difficult job, it's this rotary broach that is some kind of voodoo magic.


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## ErichKeane (Jun 10, 2021)

GunsOfNavarone said:


> Not with a 3/4"...MAYBE a half, but think about that overhang/weight. Each person could make the end that they want if it comes down to it, that's not a terribly difficult job, it's this rotary broach that is some kind of voodoo magic.


Yep, part of why I asked above   I have a drill-chuck that goes to 5/8" and one that goes to 3/4".

For me with a big lathe, it wouldn't be that bad.  Whoever gets the shank part could take orders if they cared to, otherwise I was leaning toward just designing a straight-shank.  Note the shank is what introduces the 1degree angle though.


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## GunsOfNavarone (Jun 10, 2021)

It's not the shank itself, it's the bearing block attached to it that the apparatus spins on...no?


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## GunsOfNavarone (Jun 10, 2021)

This appears to be a pressed fit...hell, you could possibly buy whatever arbor and press fit it....though that's technically cheating.


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## ttabbal (Jun 10, 2021)

My thought was 1/2" for chuck compatibility. It is true that the tool hanging out there might be an issue on smaller machines though. 

I do have a R8/MT3 adapter I've used occasionally for drill chucks on the mill. 

The taper on the print shows an M12 thread on the back. Drawbar?


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## ErichKeane (Jun 10, 2021)

GunsOfNavarone said:


> This appears to be a pressed fit...hell, you could possibly buy whatever arbor and press fit it....though that's technically cheating.
> View attachment 368825


Ah, I took that to be 1 piece.  I guess that could be press fit... though I would have thought he would have a separate drawing for separate pieces.  But yes, that part on the left of the picture introduces the 1 degree taper.


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## ErichKeane (Jun 10, 2021)

Here is my take on that rotary broach, with a few of the changes that I wanted to do (still doesn't have the 'adjuster'), and some of the dimensions aren't perfect.  

The green piece is the broach-bit.
The transparent bit is the 'body', which you can see holds everything.  It has some slotted screws so we can do adjustments.

The broach-bit goes into the spindle, which sits against the teal "needle thrust bearing", then goes through the 'body' and into the roller-bearing in the back.  What you can't see, is a retention clip holding it together.




I still have to make the flange/rear plate, plus figure out how to do the offsets.  Additionally, I probably need to spend a good while making all the dimensions 'right'.

BUT, that is my design so far.


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## ErichKeane (Jun 11, 2021)

Here is the back view, which should be a bit more clear.





Since we have quite a bit of question on the back plate/shank, I think I'll make it be 2 parts, and threaded together.  How does that sound?  That way if you find yourself really wanting an MT2 mount, you can just thread the adapter on!

I want to pick a thread, which would you prefer?  https://www.amazon.com/Morse-Taper-Adapter-Shank-Threaded/dp/B07W9L13RS?th=1

Looks like there is 1/2-20, 3/8-24 and 5/8-16.  I'm leaning toward 3/8-24 unless someone wants to go bigger-enough on the MT scale that it would be a problem.  Currently, I found an MT4 for 3/8-24 (https://www.amazon.com/Threaded-Drill-Chuck-Hardened-Adapter/dp/B015NMGBF2), so I figure that should be big enough, right?


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## ttabbal (Jun 11, 2021)

Sounds like a reasonable approach. Looks like plenty of surface area to register against, though I'm not sure concentricity is important for something you want to wobble about anyway. You could make it nice and straight if you want to!


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## ErichKeane (Jun 11, 2021)

Only current 'downside' to those adapters is I can't figure out how long the threaded section is!  Even the mcmaster version doesn't have a CAD drawing!

Unless someone orders one in advance, I'm going to have to guess.  Worst case, you might have to grind a bit off of it.


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## ErichKeane (Jun 11, 2021)

So another thing I did... Currently the "OAL" of our tool not including the backing plate, but including the tool-bit is 2.5061.  That actually ends up being SHORTER than the tool that GunsOfNaravone posted that I've been copying off of (which is 66.6mm/ 2.622").  This is despite using a slightly larger bit at 1.75" vs 35.6 mm (1.401").

I believe this means our 'offset' that we have to have against the backing plate is ~.044.  He only has 1.1mm built in (~.043"?), so I think he's counting on the oval screw-holes by quite a bit, because my calculation ends up putting him at nearly .046"?

Does someone want to check my math?  Again, tip of tool to base of flange (excluding backing plate) is 2.5061.  Angle is 1 degree.

Either way, this is quite re-assuring that we don't need much in the adjustability range.  I think I made those ovaled holes something like 30 thou in each direction! In reality, if 3 thou offset covers 60 thou in length, we don't have much to be concerned about!


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## ErichKeane (Jun 11, 2021)

Two more pictures!  If anyone wants to view the design in any format i can export (see Std Export here: https://wiki.freecadweb.org/Import_Export) let me know, and I'll post that too!  Just be kind, its only my 2nd time doing CAD.

I never put in the 'calibration' mechanism, as you guys never seemed interested in it  I can put those in somewhat easily (it complexifies making the backing plate a bit...). I'm somewhat convinced 'tapping' it in should be easy enough.

I have 2 more TODO's on this diagram:
1- I want to make the bolts come in from 'behind', it gives more room for the heads, as well as makes the math for the backing-plate less critical.
2- Wrench-flats for the backing plate.

I think the next step I want to do is order bearings to measure them and make sure of my dimensions.  

Also, out of the 4 of us (
1- ErichKeane
2- GunsOfNavarone
3- ttabbal
4- T Bredehoft)

We have to decide who is going to do which part.  Basically, you buy the materials and make your part, ship them to someone who assembles and ships.  Let me know what part you want to do, and we can sign up for them.  I can modify the design/some details based on equipment if you'd like.

1: Backing Plate : has an internal 3/8-24" thread, plus a 1 degree angle on the front, plus some corresponding holes.  Requires about a 2.5" round of steel, each part is ~3/4" long.
2: Main Body: About 2 1/8" in diameter, less than 1 1/2" long.  There are two precise internal pockets from opposite sides, the dimensions of which are somewhat reasonably meaningful, plus some tapped 1/4-28 (or 1/4-20, not sure it matters).
3: Spindle: 1-1/2" diameter 1-1/2" long.  Requires a somewhat precise 3/4" deep, 1/2" flat-bottomed hole, plus 1 fairly precise OD.  Otherwise not too bad.
4: Grinding of tool bits.  1.750" long HSS, requires a pretty accurate grinding setup, probably a surface grinder.  

As far as overall cost, there is the above materials + shipping them to me, plus:
Total cost of other parts should be cheap, I kept us to a #10 set screw, a thrust bearing ($8 for 6!), a sealed roller bearing ($9/10), a snap ring (2.35/10 + mcmaster shipping https://www.mcmaster.com/98585A109/ if someone can find an amazon link), and 4 1/4-20 or 1/4-28 bolts.


Additionally, I think we should all just decide to order our own shanks.  It looks like they are available for ~$10 each, even 1/2" arbors are available at all-industrial, as well as MT 1, 2,3, and 4  AND R8!








						All Industrial 49703 | 1/2" Straight Shank to 3/8"-24 Threaded Drill Chuck Arbor Hardened Adapter
					

We distribute top-quality industrial tools and machine shop supplies at the best prices. View our collection of CNC machinist supplies and tooling packages.




					allindustrial.com
				











						All Industrial 49710 | Threaded Drill Chuck Arbor 4MT to 3/8"-24 Hardened Morse Taper MT4 Adapter
					

We distribute top-quality industrial tools and machine shop supplies at the best prices. View our collection of CNC machinist supplies and tooling packages.




					allindustrial.com
				





Total non-materials/shipping out of pocket: 
set screw: $.50 (Guessed!)
Thrust bearing: $2 ($8 for more than we need)
Roller bearing: $2.25  ($9 for more than we need)
Snap Ring: $1 (2.35 + mcmaster shipping for more than we need)
4 bolts: $2 (another guess).
Arbor: $10
===========
$17.75.
$7.75 of which I will pre-order, so that plus whatever a flat-rate box will cost is your amount you'll eventually owe to me when we're done.


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## ttabbal (Jun 11, 2021)

I think the only part I would not be able to do would be the bit grinding. At least not with much precision. I'll say 1 or 2 since I know I have the stock. I could grab some 1.5" round though.


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## ErichKeane (Jun 11, 2021)

ttabbal said:


> I think the only part I would not be able to do would be the bit grinding. At least not with much precision. I'll say 1 or 2 since I know I have the stock. I could grab some 1.5" round though.



Cool!  Current preferences list (not signing up for both, but helps keep track):

Backing Plate: ttabbal -or- ??
Main Body:       ttabbal -or- ??
Spindle:
Bits:


Did my two TODOs for the images, going to order bearings for measuring purposes


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## GunsOfNavarone (Jun 11, 2021)

Had a 12 hour day...give me a few to read and digest the last 6 to 8 posts...


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## GunsOfNavarone (Jun 11, 2021)

Ok, a lot going on. Do you have the ability to print diagrams/plans from those CAD models? Are you saying there are only these parts (that need to be *machined*) 
Backing plate
main spindle body
spindle
angle plate
?
I wonder if this is an easy out on MAKING bits? Unless someone has a shaper or mad hand skills
Broaching bits
What else am I missing? I'd be down for making the spindle...but I'm flexible.
Also, couldn't the backing plate have a deep enough recess to handle different length threads? What is the consensus on arbor type? I'm not even sure what my machines abilities are. MT3, up to 1/2" straight...that's all?


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## ErichKeane (Jun 12, 2021)

GunsOfNavarone said:


> Ok, a lot going on. Do you have the ability to print diagrams/plans from those CAD models? Are you saying there are only these parts (that need to be *machined*)
> Backing plate
> main spindle body
> spindle
> ...


Yep, I'll make 2d prints from these once I am more sure of the dimensions and software 

There are only 3 machined parts, the back plate, the body, and the spindle. I have a surface grinder to make the bits if no one else does, so that was probably going to be my contribution.

I can definitely change the depth of the backing plate threads, I made them what I hope is deep enough. I think we are better just spending $10 and all buying our own shank.

I already ordered an MT4 and a R8 for me, so feel free to buy the 1/2" and MT2 you wanted (or I can make one or two, since the bits are perhaps too small a project).


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## T Bredehoft (Jun 12, 2021)

Let me know what I can do, I've been sidetracked, (other hobbies, not related) send me a 2d print and tell me how many to make.


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## GunsOfNavarone (Jun 12, 2021)

I have a luxury some may not, I have a Metal Supermarket about 4 miles from my house. Whatever that’s worth.
I’m flexible on what part to make…
Assign away!


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## ErichKeane (Jun 12, 2021)

T Bredehoft said:


> Let me know what I can do, I've been sidetracked, (other hobbies, not related) send me a 2d print and tell me how many to make.





GunsOfNavarone said:


> I have a luxury some may not, I have a Metal Supermarket about 4 miles from my house. Whatever that’s worth.
> I’m flexible on what part to make…
> Assign away!



Ok, then I think I'll give @GunsOfNavarone the main body as it requires a slightly larger diameter stock, and @T Bredehoft can have the spindle.

Backing Plate: @GunsOfNavarone 
Main Body:       @ttabbal 
Spindle: @T Bredehoft
Bits: @ErichKeane

Don't buy materials until I have the prints done, I want to make sure I've got the sizes of everything where it needs to be.  I should be getting all the bearings in by Monday, so I should be able to confirm my measurements by then and start on the prints.  After that, the dividing head project had everyone inspect to make sure they would be able to make what they were given.


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## GunsOfNavarone (Jun 12, 2021)

We need to send you money for things...I seem to remember reading some posts back. Method and amount please?


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## ErichKeane (Jun 12, 2021)

GunsOfNavarone said:


> We need to send you money for things...I seem to remember reading some posts back. Method and amount please?


I'll just have you send it at the end as I'm not sure how much the 'shipping back' is going to be.  I think it ends up being ~$20/each at the end though.  I figure paypal or mail when we get there.


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## GunsOfNavarone (Jun 12, 2021)

So to be clear, this is the list;

1- ErichKeane-cutting bits (better be one damn extensive set!)   ; )  #3 on diagram and misc bearings/screws
2- GunsOfNavarone Backing/angle plate Part #1 on diagram
3- ttabbal spindle housing
4- T Bredehoft) sindle


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## ErichKeane (Jun 12, 2021)

GunsOfNavarone said:


> So to be clear, this is the list;
> 
> 1- ErichKeane-cutting bits (better be one damn extensive set!)   ; )  #3 on diagram and misc bearings/screws
> 2- GunsOfNavarone Backing/angle plate Part #1 on diagram
> ...


Yep, pretty much  I'm going to make 2-3 sizes of bits to start, and otherwise make them compatible with the commercial/professional 1/2" diameter bits (which are 1.75" long).

McMaster has a bunch of them available at roughly $100/each, but at least they are available.

I noticed while designing this that a bunch of the designs use non-standard bits that you basically need to grind yourself, so having commercially available alternatives was important to me.

One such concern is that if you grind yourself (and don't have a cyndrilical grinder!) You are stuck to the 1/2" major size (so .433 hex or so).  You'll note that the TomMakesHere has that problem (and is a non-standard size, so you're stuck with those.).


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## GunsOfNavarone (Jun 12, 2021)

Hmmmm...interesting and concerning. I don't do HSS, say on  my mill, as I do not have sharpening skills, I go carbide inserts. So, I won't be sharpening bits, I'll be buying new ones. $100 a pop??! I guess I should do some searches for .500" broaching bits....there has got to be a reasonable source somewhere!


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## ErichKeane (Jun 12, 2021)

GunsOfNavarone said:


> Hmmmm...interesting and concerning. I don't do HSS, say on  my mill, as I do not have sharpening skills, I go carbide inserts. So, I won't be sharpening bits, I'll be buying new ones. $100 a pop??! I guess I should do some searches for .500" broaching bits....there has got to be a reasonable source somewhere!


Yeah, bits for these are expensive! Fortunately minor dressing of them ends up being just a stone across the flats.

My idea was to custom make 2-3 for each of us (square or hex!) That should cover us. Sadly, there doesnt seem to be any Chinese manufacturers of these.

If you have the ability to harden O1 you could make them out of that, or potentially use carbide to cut the hss. I'm using my surface grinder with a diamond wheel I think.


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## ErichKeane (Jun 12, 2021)

This place : has them ft $50 each! https://www.polygonsolutions.com/ro...ches/hexagon-rotary-broaches-half-inch-shank/

They even have through-hole versions, which have the ability to go into a tighter hole, since the air can escape backwards!


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## GunsOfNavarone (Jun 12, 2021)

I gotta say...their adjustment free holder sounds pretty awesome. I really am a bit lost as to why a small amount of movement of the spindle (radially-so the broach can center itself), isn't possible for us (?)


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## ErichKeane (Jun 12, 2021)

GunsOfNavarone said:


> I gotta say...their adjustment free holder sounds pretty awesome. I really am a bit lost as to why a small amount of movement of the spindle (radially-so the broach can center itself), isn't possible for us (?)


Do they have a good image of one that I can perhaps see to copy? I just was on my phone and saw they have bits at 1/2 of McMaster prices.


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## Ianagos (Jun 12, 2021)

ErichKeane said:


> This place : has them ft $50 each! https://www.polygonsolutions.com/ro...ches/hexagon-rotary-broaches-half-inch-shank/
> 
> They even have through-hole versions, which have the ability to go into a tighter hole, since the air can escape backwards!



Their broaches are ok I’ve purchased a few at the tune of $70-$80 each.

Their m2 broach literally deformed like mild steel I thought it was wild I’ve never seen hss do that???? Must have been some cheap Chinese stuff. They told me the higher grade stuff was better but I never got to use it.


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## T Bredehoft (Jun 13, 2021)

Broaches.. I can't imagine using as large as 1/4, I don't work with screws that large (3/8) although I probably could. Most of my projects use screws smaller than 1/4-20. down to and including 4-40. I have tapped holes 2-56, but certainly never will make a screw that small.

Send me a finished print and some steel, I'm ready. Oh, what are we making this out of? I'd suggest either annealed of half hard 4140 or such. If this has been discussed, I missed it, sorry.


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## ErichKeane (Jun 13, 2021)

T Bredehoft said:


> Broaches.. I can't imagine using as large as 1/4, I don't work with screws that large (3/8) although I probably could. Most of my projects use screws smaller than 1/4-20. down to and including 4-40. I have tapped holes 2-56, but certainly never will make a screw that small.
> 
> Send me a finished print and some steel, I'm ready. Oh, what are we making this out of? I'd suggest either annealed of half hard 4140 or such. If this has been discussed, I missed it, sorry.


Any sort of steel works, nothing on the tool other than the bit has a critical hardness.  1018/12L14 works, as does 4140.


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## rwm (Jun 13, 2021)

I like you design but I have one question. Is there something that retains the spindle so it doesn't get pulled out? When I use my broach, the cutter sometimes gets stuck in the hole and traction is required to remove it. There could be significant pull on the spindle.
Robert

EDIT: Never mind! I missed part #9 the clip. That looks good.
Robert


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## GunsOfNavarone (Jun 13, 2021)

The no center broach was the same place as the link you gave for $50 bits. 
What type of steel? I agree, not a lot of beatings going on here, but I would think bearing surfaces should be hard/hardened...if we plan on making this a quality tool that is handed down and such.


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## ErichKeane (Jun 13, 2021)

rwm said:


> I like you design but I have one question. Is there something that retains the spindle so it doesn't get pulled out? When I use my broach, the cutter sometimes gets stuck in the hole and traction is required to remove it. There could be significant pull on the spindle.
> Robert
> 
> EDIT: Never mind! I missed part #9 the clip. That looks good.
> Robert


Yep, there is a snap ring at the back of the spindle   The bit is held in by a set-screw, though I want to do some slight changes to the model (hopefully not making it too much longer!) to make sure it hits the 'flat' right on most commercial bits.




GunsOfNavarone said:


> The no center broach was the same place as the link you gave for $50 bits.
> What type of steel? I agree, not a lot of beatings going on here, but I would think bearing surfaces should be hard/hardened...if we plan on making this a quality tool that is handed down and such.
> 
> View attachment 369033
> View attachment 369034



I don't see hardening the surfaces as necessary, we have hardened races on the bearings, so those should be the frictions surfaces.

I looked at that design quite a bit, and I just don't see how they get away with no adjustment unless they are simply counting on more accurate machining/tool lengths.  I calculated that every 'thou' is worth quite a bit in length, which makes me think the calibration is just less important than a lot of these youtubers are making it seem.  Based on my math in a post a bit above, Each 'thou' of offset covers something like 50 thou of length.  

2.5" is 43.6 thou, 2.6" is 45.4 thou offset, so I suspect the calibration is just way less important after the 1st time than the drawings all seem to make it seem.


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## rwm (Jun 13, 2021)

I now think you are correct about the precision of the offset not being so critical. The Sine of 1 deg is a pretty small number and there is some flex in any setup. Your design is gonna work great.
Robert


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## ErichKeane (Jun 13, 2021)

rwm said:


> I now think you are correct about the precision of the offset not being so critical. The Sine of 1 deg is a pretty small number and there is some flex in any setup. Your design is gonna work great.
> Robert


Thanks for the confirmation! I'm thinking of simplifying the back plate to remove the slots and replace with slightly oversized holes instead (plus the built-in-offset), since that should get us close enough.


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## rwm (Jun 13, 2021)

The amount of offset you will need should be Sin 1 x length from backplate to tip of broach. That would tell you how much adjustment you will need. What is that distance?
R


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## ErichKeane (Jun 13, 2021)

rwm said:


> The amount of offset you will need should be Sin 1 x length from backplate to tip of broach. That would tell you how much adjustment you will need. What is that distance?
> R


Yep, that's the math I came out with. Currently in the design it is 2.5061" (if I remember correctly) for 43.7 thousandths.

I had designed in a adjustment range of 150 thou (plus the fit of a 1/2-28" in a 1/4" hole), but reduced the slot to .35" as the design finished. I suspect I'd be better off making it an F or G instead, and simplifying @GunsOfNavarone s work!


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## GunsOfNavarone (Jun 13, 2021)

Maybe some ideas....
Broach
Also some good info on making the actual cutting bits.


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## ErichKeane (Jun 13, 2021)

GunsOfNavarone said:


> Maybe some ideas....
> Broach
> Also some good info on making the actual cutting bits.


I actually got that in my feed a few days ago   My plan was going to be to rough it out on my bench grinder (for the smaller bits), then finish using my magnetic sine plate (with a machinist vise on it most likely), then use my hex/square collet-blocks to get the angles right.  Overall size is easy enough to get it seems, it is just a matter of sneaking up on it I expect.


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## ErichKeane (Jun 13, 2021)

Good news! Bearings all showed up today and measure about what I hoped they would! I have a couple small changes to make, but I should be able to start on 2d drawings this week!


Also good news.. I played with it a bit and took about the OAL down another 70 thou. There is a spot to take it down another perhaps 150 thou, but I like the 200 thou wall between the back of the broach and the rear bearing.

I still need to adjust the offset because of that, and fixup the holes on the backing plate, then I can start drawing  We will see how this goes, I'm excited to see how well the design holds up against reality.


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## GunsOfNavarone (Jun 13, 2021)

I see you are crunching numbers on shortening the OAL. I was considering allowing some extra thickness on the backing plate so no matter if the arbor is .625 or .750 long (threaded shank), it could be tightened down with no worry of bottoming out. Also, I now the off center is taking up it's part of the pre planning, what if the backing plate had a boss and the spindle body was recessed and you could have 4 sets screws around the outside for centering?
I.E. below. The boss could still be ground with the 1* of angle


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## ErichKeane (Jun 13, 2021)

GunsOfNavarone said:


> I see you are crunching numbers on shortening the OAL. I was considering allowing some extra thickness on the backing plate so no matter if the arbor is .625 or .750 long (threaded shank), it could be tightened down with no worry of bottoming out. Also, I now the off center is taking up it's part of the pre planning, what if the backing plate had a boss and the spindle body was recessed and you could have 4 sets screws around the outside for centering?
> I.E. below. The boss could still be ground with the 1* of angle
> 
> View attachment 369084


Something like that recess was one of my thoughts on that. But the more I see it, I wonder how much this would be something we do!

I have a boss built into the backing plate for the arbor, but note the backing plate thickness doesn't matter for the offset. The important "length" is front of backing plate to tip of bit. So any additional thickness to the backing plate is fine.


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## GunsOfNavarone (Jun 14, 2021)

So this offset thing is new to me in regard to the rotary broach. Those of you that have more understanding of it, chime in. I just want to make sure all challenges are addressed so we don't have one of those, "I wish we would have done..."
A thicker back plate would allow a hole of varying depth for different arbors.


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## ErichKeane (Jun 14, 2021)

GunsOfNavarone said:


> So this offset thing is new to me in regard to the rotary broach. Those of you that have more understanding of it, chime in. I just want to make sure all challenges are addressed so we don't have one of those, "I wish we would have done..."
> A thicker back plate would allow a hole of varying depth for different arbors.


I've already got the 'bore' area for the arbor at ~.750 (with some room to go deeper).  Presumably a washer could be used to make it longer if necessary.

Currently I'm wrestling with FreeCad's TechDraw to try to make 2d drawings that aren't terrible looking.  I think I made a mistake trying to do the backing plate first   The 1 degree angle confuses the heck out of the drawing panel in a number of different ways!

The way it lists tolerances are a little strange too, so I'm still working through that too.  That said, I think I am doing a good job identifying the 'important' dimensions, with most of my dimensions as "unimportant".  For example, on the backing plate, the 1 degree angle is critical, as are the bolt-hole spacing, otherwise we're looking at mostly 'fractional-ish' dimensions.  I still can't figure out how to show fractional dimensions either though


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## ErichKeane (Jun 14, 2021)

alright, drawings "done" ish.

Please review these images and let me know if they have enough information.  THis is still my first try at CAD, so i could still have messed stuff up.


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## T Bredehoft (Jun 15, 2021)

While your drawings are like mine, not professional, they show what is needed.

Got my Spindle drawing, are we going to leave them round (1.50) or.... what.?  I see the spindle  dwg doesn't show the through holes/slots.


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## ErichKeane (Jun 15, 2021)

T Bredehoft said:


> While your drawings are like mine, not professional, they show what is needed.
> 
> Got my Spindle drawing, are we going to leave them round (1.50) or.... what.?  I see the spindle  dwg doesn't show the through holes/slots.


Yep, the spindle is round (1.5" OD at the largest spot).

There are only two inner bores plus a set-screw, which are on the right image, though the renderer apparently made them look a lot like the 'measurement' lines.  

In the 'face' side, there is a .500 +.010/-0 diameter bore, .750 deep, with a square bottom.  In addition, there is a .125 (or so, the diameter doesn't really matter since this an 'air relief' hole) bore all the way through (#3 in the drawing).


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## T Bredehoft (Jun 15, 2021)

And what keeps it from  revolving independent of the Main Body?


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## ErichKeane (Jun 15, 2021)

T Bredehoft said:


> And what keeps it from  revolving independent of the Main Body?


Nothing, the intent is to have the spindle revolve independently of the main-body.  It is on 2 bearings intended to let that happen.


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## rwm (Jun 15, 2021)

In my mind, the way a rotary broach engages a hole is kind of like a U joint on a car. The axes of rotation are angled with respect to each other but the axes intersect at a point that is the tip of the cutter. 
Robert


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## T Bredehoft (Jun 15, 2021)

ErichKeane said:


> Nothing, the intent is to have the spindle revolve independently of the main-body.  It is on 2 bearings intended to let that happen.


Hmmmm...OK.


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## ttabbal (Jun 15, 2021)

Drawings look easy enough to follow. Which one should I be looking at making? I'll pay extra attention to it.


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## ErichKeane (Jun 15, 2021)

ttabbal said:


> Drawings look easy enough to follow. Which one should I be looking at making? I'll pay extra attention to it.


You are the 'main body'.  The MOST important dimension there is the needle bearing's back (front bearing) to the rear-most location.  The needle bearing thickness has the +/- 3 thou because if you're too long you end up hitting the spindle.

The bolt holes are all tapped 1/4-28, and their location is pretty important.

Otherwise, I think I have enough clearance in places to make the rest of it pretty unimportant.

BTW: Any dimension that I didn't specify tolerances on is pretty unimportant, I designed this like I was going to be making all the parts, which means I put plenty of clearance on most dimensions


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## ttabbal (Jun 15, 2021)

The 3 bore diameters result in a through hole, right? Doesn't look bad at all. When we get ready to go, please post the 3D model. It helps to be able to turn it around and look from all sides.


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## ErichKeane (Jun 15, 2021)

ttabbal said:


> The 3 bore diameters result in a through hole, right? Doesn't look bad at all. When we get ready to go, please post the 3D model. It helps to be able to turn it around and look from all sides.


Yes, that is correct. 

I'll definitely do so, what format do you prefer?  I can post it pretty easily in a couple of formats.


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## ErichKeane (Jun 15, 2021)

Also note, I just got in the R8 arbor with 3/8-24 thread on it that I ordered (I also have an MT4 incoming).  The threads on this one are .555 long or so, so the .750 that I left for them should be plenty assuming everyone else's shanks are the same.  @GunsOfNavarone


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## ErichKeane (Jun 15, 2021)

I attached the STEP file, but I don't have anything to view it, so hopefully it turned out OK


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## rwm (Jun 15, 2021)

Look s good to me. Opens fine on Fusion.
R


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## ttabbal (Jun 16, 2021)

FreeCAD can do it too. Fusion is nicer though because you can view only the part you want to see. I could have missed an option in FreeCAD. Anyway, looks good.


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## ErichKeane (Jun 16, 2021)

ttabbal said:


> FreeCAD can do it too. Fusion is nicer though because you can view only the part you want to see. I could have missed an option in FreeCAD. Anyway, looks good.


ON the left bar (at least during design in the normal files) there is the ability to disable each component 1 by 1.

I used FreeCAD because I'm on Linux, so most cad packages aren't an option.


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## ttabbal (Jun 16, 2021)

ErichKeane said:


> ON the left bar (at least during design in the normal files) there is the ability to disable each component 1 by 1.
> 
> I used FreeCAD because I'm on Linux, so most cad packages aren't an option.



Yeah. I run Linux as my main OS. I have Windows in VMs though, just for some things that work better that way for me. I even have an extra GPU and pass it into the win VM for performance. 

I expected FreeCAD to do that, but it just shows one body "Rotary Broach". In Fusion it shows the individual bodies so you can select them. It seems like it should be possible. It's probably an option or something. I think it's great to see more being done with FreeCAD. I think it has a lot of potential.


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## ErichKeane (Jun 16, 2021)

Ah, well, I'm just on an old i5 laptop from 2014, so running a windows VM is a little too much for it   If you want the freecad file I can definitely share that as well.


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## ErichKeane (Jun 16, 2021)

Alright, I just got my other arbor in (the MT4 one!), and it is also only a little more than !/2" thread length, so the .750 we have is way more than enough.  @GunsOfNavarone  feel free to make the backing plate a bit thinner if you'd like  

I also ordered the drill rod.  It is quite expensive ($15+shipping for enough to make 3 bits for HSS!), but I have enough to make 3 for everyone.  Still soliciting size-preferences for all of you  

I also figure we'll go another few days giving you guys time to check out the plans to make sure it works for everyone (and @ttabbal/@rwm to check my drawings  ) , and we can start working!

No real rush on this, I figure it'll take me a while to get materials in and I'll probably spend a solid evening on each of the bits anyway, so it'll take a while for my part to be done anyway!


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## GunsOfNavarone (Jun 16, 2021)

Sorry...I was busy on my own projects (I set aside 20 hours a week mandatory for straight shop work...I have really picked up momentum since)
Just caught up, down loaded prints and step. File. I will take a look at step file and print the.....prints? {shrug)


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## ttabbal (Jun 16, 2021)

I've got mine on paper, so unless you have changes, I think I'm good to go.


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## GunsOfNavarone (Jun 16, 2021)

So I am just poking around for the stock. What type metal can we all agree on? i.e. I can get enough 4140 to do 5 of these backing plates.
1018 sucks..... don't wanna go there...especially hot rolled. If I was making this for myself...I'd use stainless and pass it down to my dog when I die.
What ya'll thinking here (cost being a consideration is fine) On that note, should we all just keep a ledger of what we spend? Whomever spends the most, we divide that overage by the others and subtract what we spent? This is my one hobby/meaning for life so I allow myself whatever I see fit.


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## GunsOfNavarone (Jun 16, 2021)

ErichKeane said:


> Alright, I just got my other arbor in (the MT4 one!), and it is also only a little more than !/2" thread length, so the .750 we have is way more than enough.  @GunsOfNavarone  feel free to make the backing plate a bit thinner if you'd like
> 
> I also ordered the drill rod.  It is quite expensive ($15+shipping for enough to make 3 bits for HSS!), but I have enough to make 3 for everyone.  Still soliciting size-preferences for all of you
> 
> ...


So the MT4 is great for lathe, but do you never plan on using it on a mill? Is MT4 common on a mill? Either I want to get 2 arbors (an MT and a straight shank) if I can get them on same diameter shank/pitch.


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## ErichKeane (Jun 16, 2021)

GunsOfNavarone said:


> So the MT4 is great for lathe, but do you never plan on using it on a mill? Is MT4 common on a mill? Either I want to get 2 arbors (an MT and a straight shank) if I can get them on same diameter shank/pitch.


I bought an MT4 and an R8 for mine. Arbors go for $10 each or so, so I suggested everyone just buying one/two if they wanted.


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## GunsOfNavarone (Jun 16, 2021)

My most realistic choice would be 12L14...great for machine tools and very machinable...


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## GunsOfNavarone (Jun 16, 2021)

ErichKeane said:


> I bought an MT4 and an R8 for mine. Arbors go for $10 each or so, so I suggested everyone just buying one/two if they wanted.


What are the thread diameters and pitch?


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## ErichKeane (Jun 16, 2021)

GunsOfNavarone said:


> My most realistic choice would be 12L14...great for machine tools and very machinable...



Yep, just about any steel would be perfect!  I tend to best be able to hold dimensions in 12L14, so I'd lean toward that.  Else I tend to use cold-roll (or 4140 when I'm feeling extra fancy).



GunsOfNavarone said:


> What are the thread diameters and pitch?


3/8-24. If you want to use something else, the backing-plate is the one with the threaded hole in it, so you can do yours differently  

I chose 3/8-24 since it had the widest range/variety of options, from MT1 to MT4, as well as R8 and a bunch of straight shanks.


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## ttabbal (Jun 16, 2021)

The material I have is unknown for sure. Ferric Unknownium.   

Some steel anyway. If everyone would prefer something else, I can likely find something..


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## GunsOfNavarone (Jun 17, 2021)

I ordered 12L14 stock, says it will be here by 24th, but I suspect a couple days earlier.
I looked for an MT3 to 3/8” arbor, nothing on Amazon though there is a 14mm which is a bit beefier, maybe I’ll go that route…I’ll keep poking around.


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## ErichKeane (Jun 17, 2021)

GunsOfNavarone said:


> I ordered 12L14 stock, says it will be here by 24th, but I suspect a couple days earlier.
> I looked for an MT3 to 3/8” arbor, nothing on Amazon though there is a 14mm which is a bit beefier, maybe I’ll go that route…I’ll keep poking around.


I see this one for $12: https://www.amazon.com/Arbor-Drill-Chuck-Tang-Thread/dp/B01NBJGX2L

The keywords are basically "3/8-24 MTx Arbor" on google and that comes up with all the MT1-4 and R8 (plus many others).

3/8-24 is a really common drill chuck arbor thread, so they come up for those.


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## GunsOfNavarone (Jun 17, 2021)

Weird, I searched for MT3 to 3/8” arbor and nada. Looking at that, it seems that recessing the threads in order to let the boss seat with inside of the backing plate would be ideal, but that would double thickness. I’ll stick to the plans…


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## GunsOfNavarone (Jun 17, 2021)

I'm dinking around with the step file and I'm a bit confused. I know there was discussion with offset an I just smiled and looked pretty as I had no idea WTH you guys were talking about. On this drawing, which mostly agrees with yours....is this strange hole pattern anything to do wit that?
I assume the body will have this spacing as well? I'm not seeing it on those plans. This seems error-ish (?)
	

		
			
		

		
	



**EDIT** going back to the prints (as for whatever reason-the computer version is blacked out) I see some notes as to this being by design. I stand by WTH, as I am perplexed as it's the 1 degree thickness the spindle spins on that causes the in/out cutting motion. I don't understand the hole offsets. This will only allow the body to bolt up one way...but why? Everything is centered on rotational axis. Should I continue to look pretty and just do as I'm told? I'm ok with the short answer....


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## ErichKeane (Jun 17, 2021)

GunsOfNavarone said:


> I'm dinking around with the step file and I'm a bit confused. I know there was discussion with offset an I just smiled and looked pretty as I had no idea WTH you guys were talking about. On this drawing, which mostly agrees with yours....is this strange hole pattern anything to do wit that?
> I assume the body will have this spacing as well? I'm not seeing it on those plans. This seems error-ish (?)
> 
> 
> ...



Note that this seems to be 'on axis' rather than on-angle, the face is at a 1 degree angle, so I think the measurements might be a touch off.  It is supposed to be biased 42 thou I think (so .742/.658?).

Holes are spaced in a 1.400 square.  However, this square isn't 'centered', it is shifted "up" (in this case to the left?) on the 'thicker' side of the 1 degree angle.  This offset moves the 'body' upwards (again, toward the thicker side of the backing plate) to make up for the 1 degree angle across the face.  The idea is that the broach bit has to be 'centered' on the axis of the shank, but approach the material at a 1 degree angle.


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## GunsOfNavarone (Jun 17, 2021)

Ok...that makes good sense, thanks for clearing it up.


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## GunsOfNavarone (Jun 17, 2021)

Next question...body says it is drilled for 1/4 x28 4 bolt pattern (I don't believe it says tapped as well), but the back plate says 1/2 x 28 (which I can't find even existing on my calc program) and when I model in F360, that hole is way too huge for area. Should this be 1/4 x 28 in backing plate? It says clearanced so I assume it also is not threaded? No threads body, no threads plate? I promise I'm getting MOST my questions out now.


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## ErichKeane (Jun 17, 2021)

GunsOfNavarone said:


> Next question...body says it is drilled for 1/4 x28 4 bolt pattern (I don't believe it says tapped as well), but the back plate says 1/2 x 28 (which I can't find even existing on my calc program) and when I model in F360, that hole is way too huge for area. Should this be 1/4 x 28 in backing plate? It says clearanced so I assume it also is not threaded? No threads body, no threads plate? I promise I'm getting MOST my questions out now.


Woops!  Yeah, the bolt holes in the body should be drilled/tapped 1/4-28, and the backing plate should be clearance-drilled "G" (to allow a little wiggle/calibration room).

The bolts go through the backing plate, and into the 'main body' (which should be tapped for that).  Other designs have bolts coming in from the front, but it results in the 'flange' needing to be significantly larger.


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## Shotgun (Jun 18, 2021)

I'm tied up with the dividing head project, or I'd love to join this one.  But, I've been reading every word of the thread.

The 1 degree face seems like it would be hard to make, and then locks the user into using a precise length of broach.   I was thinking that you could machine it square, and then insert a washer between the backing plate and body.  The typical washer is .062" thick, but there are thin washers half that.  On the bolt circle, you'd want a thick one, then a thin on the two neighboring ones, then no washer on the last.

Also, machining a shallow cup at each bolt hole in the body, along with a half ball on the socket head screws would account for the tilting.


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## Shotgun (Jun 18, 2021)

Also, if you did it this way, remove the offsetting washers and you have a free live center.

(Watched Joe Py video a couple days ago, and was wondering why it looked so familiar.)


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## ErichKeane (Jun 18, 2021)

Shotgun said:


> I'm tied up with the dividing head project, or I'd love to join this one.  But, I've been reading every word of the thread.
> 
> The 1 degree face seems like it would be hard to make, and then locks the user into using a precise length of broach.   I was thinking that you could machine it square, and then insert a washer between the backing plate and body.  The typical washer is .062" thick, but there are thin washers half that.  On the bolt circle, you'd want a thick one, then a thin on the two neighboring ones, then no washer on the last.
> 
> Also, machining a shallow cup at each bolt hole in the body, along with a half ball on the socket head screws would account for the tilting.


The length of the bit doesn't have to be too precise, a few tens of thou is fine.

The problem with making the angle adjustable is that the angle is extremely important in relatio ln to the relief of the bit, AND then changes the offset. So you'd then have two adjustments you need to make.

Having the offset be adjustable is what most designs usually go with.


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## ErichKeane (Jun 22, 2021)

Ok, I think we're about ready to build, right?  The only clarification seems to be that the body's 4 holes need to be tapped 1/4-28, and that the backing plate is 1/4-28 clearance holes (I specified 'G', but feel free to mess with that a touch).

Anyone else have other concerns/questions?

I got my HSS blanks in last night, but thanks to the dividing head project am likely a little bit of time from making my parts.  Additionally, I still need 3 bit size/shape-requests from everyone.  Options are basically: 

-Hex: Any size up to ~.433 across the flats.
-Square: Any size up to ~.353 across the flats.

For me, I'm probably going to do:
1/4" Square
3/8" Hex
3/16" Hex


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## T Bredehoft (Jun 22, 2021)

I can't see use for me other than small Allen holes, 3/16, 5/32, 1/8.


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## ttabbal (Jun 22, 2021)

The ones you listed look good to me @ErichKeane. I think the drawing makes sense, so I should be able to cut from it fine. I'll work on a prototype and update here should I run into anything.


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## GunsOfNavarone (Jun 22, 2021)

I got the steel in yesterday, cut a 1” slab off.  I do want to clarify hole positions. I get they should favor the thicker side of the angled plate, but couldn’t you offset the holes on the body? This way the body and backing plate with more or less alight on the outside edge? Why the holes aren’t evenly spaced and just drill a bit off center….I’m perplexed.
As for sizes…are metric ok? I’d say 3, 4 & 5 mm ?


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## ErichKeane (Jun 22, 2021)

GunsOfNavarone said:


> I got the steel in yesterday, cut a 1” slab off.  I do want to clarify hole positions. I get they should favor the thicker side of the angled plate, but couldn’t you offset the holes on the body? This way the body and backing plate with more or less alight on the outside edge? Why the holes aren’t evenly spaced and just drill a bit off center….I’m perplexed.
> As for sizes…are metric ok? I’d say 3, 4 & 5 mm ?
> 
> 
> ...


As long as there is an offset, yes.  I chose to do it in the backing plate just because most designs seem to introduce the offset there.  Doing the offset in the base wouldn't correct the ODs though, since it would still be offset.

I'm not sure what you mean by 'evenly spaced and drilled off center'?  They are evenly spaced compared to eachother (a 1.4" 'square') AND are drilled off center (~43 thou toward the thickest side).

As far as the drill bit size, it is just clearance hole with some wiggle room for a 1/4-28, so it would have to be a 6.5mm at minimum.


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## ErichKeane (Jun 22, 2021)

1 big problem with doing the offset in the base is it would require its flange to be bigger to account for that.  The bolt-circle is currently about the smallest size we can get away with to save from going too big on that part.


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## GunsOfNavarone (Jun 23, 2021)

Alright, I’m gonna knock one out tomorrow, if all is well, how many more? 4 correct? Or was it 4 total?


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## ErichKeane (Jun 23, 2021)

GunsOfNavarone said:


> Alright, I’m gonna knock one out tomorrow, if all is well, how many more? 4 correct? Or was it 4 total?


4 Total!


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## T Bredehoft (Jun 23, 2021)

Where do I get material for my spindles?


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## ErichKeane (Jun 23, 2021)

T Bredehoft said:


> Where do I get material for my spindles?


I like speedymetals or if desperate, McMaster. Sometimes ebay has good deals too.


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## Ianagos (Jun 23, 2021)

T Bredehoft said:


> Where do I get material for my spindles?



Online metals can be good if you have coupons. For small
Amounts sometimes they are high though


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## GunsOfNavarone (Jun 24, 2021)

Amazon and eBay are also good…
So just kinda taking this slow…guess my biggest girdle is swapping between machines and getting center close as possible.


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## GunsOfNavarone (Jun 24, 2021)

I have to come back once it cools and do a final pass on X & Z. Don’t want thermal expansion to have more bearing than it has too.


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## GunsOfNavarone (Jun 24, 2021)

We have .044” on this 1st part. I hope the learning curve is quick and they improve. I’m not THRILLED with the finish on 12L14…seems more like 1018. I want my CNC mill to do the drilling and tapping, so finding center will be key. I have a passive probe so that aught to help.


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## ErichKeane (Jun 24, 2021)

GunsOfNavarone said:


> We have .044” on this 1st part. I hope the learning curve is quick and they improve. I’m not THRILLED with the finish on 12L14…seems more like 1018. I want my CNC mill to do the drilling and tapping, so finding center will be key. I have a passive probe so that aught to help.
> 
> 
> 
> ...




Note there is no tapping!  The backing plate is through-holes.

Also note that the only dimensions with any real tolerance are the 3/8-24 threads, the 1 degree angle, and the clearance-hole locations.  The rest is suggestions (I think I mentioned any dimension without tolerances was basically +/- whatever).


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## GunsOfNavarone (Jun 24, 2021)

I mean tapping the arbor hole only….
As I’m kinda learning as I go here, this 1st one will be the loosest on specs. Now I know we all are kind of speculating what the angle should be and how much adjustment we might have to work with or against the angle. That leads to the clearanced holes. I was thinking of running them at .266” being this first one is .002 imbalance thickness over what the guesstimate was and I might have one at .001 under. How much wiggle room will we need to off set that little amount of thickness difference over 2.5”…???
I think this is everyone’s first shot making a rotary broach…..hell, probably using one too!
I have the programming done for the mill, but I really need another set of soft jaws 1st…mine are on their 3rd use for custom jaws. Worth it for 4 of these. I think the next 3 will probably only take 1.5 hours max each. Don’t worry,  I’ll keep the loosest spec version for myself…b/c I’m like that.


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## ErichKeane (Jun 24, 2021)

GunsOfNavarone said:


> I mean tapping the arbor hole only….
> As I’m kinda learning as I go here, this 1st one will be the loosest on specs. Now I know we all are kind of speculating what the angle should be and how much adjustment we might have to work with or against the angle. That leads to the clearanced holes. I was thinking of running them at .266” being this first one is .002 imbalance thickness over what the guesstimate was and I might have one at .001 under. How much wiggle room will we need to off set that little amount of thickness difference over 2.5”…???
> I think this is everyone’s first shot making a rotary broach…..hell, probably using one too!
> I have the programming done for the mill, but I really need another set of soft jaws 1st…mine are on their 3rd use for custom jaws. Worth it for 4 of these. I think the next 3 will probably only take 1.5 hours max each. Don’t worry,  I’ll keep the loosest spec version for myself…b/c I’m like that.


Ah right I forgot about that  note the tapped hole is square to the back, not the angle( though the clearance holes ARE square to the angled surface).

I'm not sure what you mean by the rest of the questions? The offset matters, the size of the holes is just clearance for a .250 hole with some wiggle room to make up for the offset not being perfect or the body holes not being perfectly on pattern.

The angle itself (the 1 degree angle) is pretty critical within a few minutes. Too little and the tool pressure will be too high, too much and the clearance angle in the cutter won't be sufficient.

If out of spec too much in either direction, thenoffset is wrong.


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## ttabbal (Jun 24, 2021)

For the main bores in the body, is conctricity critical? I think one of the bores is going to be from the back, I can certainly center it in the 4jaw, just checking if I need to hold tight tolerance for it.


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## GunsOfNavarone (Jun 24, 2021)

@ttabbal   I'm gonna say since bearings reside in the body, concentricity is important. 
As far as wiggle room on holes in backing plate, I'm getting (reading) .250" to .266" on the 1/4" screws. I was thinking of counterboring them a bit...nay, yay?
Here is "close' and "loose" tolerance. I think since this is our first attempt at the theoretical, more wiggle room over less. If I hear no arguments from anyone, .266" is it.


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## ErichKeane (Jun 25, 2021)

ttabbal said:


> For the main bores in the body, is conctricity critical? I think one of the bores is going to be from the back, I can certainly center it in the 4jaw, just checking if I need to hold tight tolerance for it.


It isn't particularly important, a few thou Esther way is going to be fine. The rear bore is for the bearing, which is the only fixture holding the bit "centered". I intentionally did that to try to give us a little wiggle room in getting the offset right.

I might suggest doing the .750 through bore and the rear most bearing bore in the same operation, since those are the most inportant concentricity wise. That .750+ is so that the spindle's .750- had a spot to go, so we might "miss" the bearing otherwise.

The front bore OD is a clearance hole for the thrust bearing, so it doesn't index on anything at all. If it is out of center or over spec, it won't matter one iota.


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## ttabbal (Jun 25, 2021)

Cool. That helps. I would like to keep everything as close as possible, but there's always tolerance somewhere.


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## ErichKeane (Jun 25, 2021)

ttabbal said:


> Cool. That helps. I would like to keep everything as close as possible, but there's always tolerance somewhere.


I designed this like _I_ was making it, so there is basically 1-2 important dimensions on everything at most


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## ttabbal (Jun 25, 2021)

And I present a boring photo... 





Bore measures 0.752, but is a bit warm so I'll double check it in a few minutes after cooling. Then the bearing pocket on the back before flipping the part for the front features.


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## GunsOfNavarone (Jun 25, 2021)

I feel like I should be knocking these out now, but now that I have he ops down, its only a few hours work. I did measure the angle with a digital angle gauge of the "prototype" plate I made. I actually have (not the thickness) an angle of 89* and when I flipped it...91* but now I'm perplexed. Do I run at the .045" imbalance I purposely used or do I drop it down to .042" as planned. I can always remake mine real quick so I'll keep mine as is and we'll all compare notes I guess.
What steel did you use @ttabbal  ?


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## GunsOfNavarone (Jun 25, 2021)

ErichKeane said:


> I designed this like _I_ was making it, so there is basically 1-2 important dimensions on everything at most


Did I get the only to "important dimensions"?  Those bit have got to be a bit an the unforgiving side!


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## ErichKeane (Jun 25, 2021)

GunsOfNavarone said:


> I feel like I should be knocking these out now, but now that I have he ops down, its only a few hours work. I did measure the angle with a digital angle gauge of the "prototype" plate I made. I actually have (not the thickness) an angle of 89* and when I flipped it...91* but now I'm perplexed. Do I run at the .045" imbalance I purposely used or do I drop it down to .042" as planned. I can always remake mine real quick so I'll keep mine as is and we'll all compare notes I guess.
> What steel did you use @ttabbal  ?


I had figured you would use a sine bar to set the angle, it should be pretty straight forward I'd you have one. I've not considered what doing a angle gauge would do...


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## ErichKeane (Jun 25, 2021)

GunsOfNavarone said:


> Did I get the only to "important dimensions"?  Those bit have got to be a bit an the unforgiving side!


Each part has a couple.

The backing plate has the angle + the offset.

The body has the OAL (well, back to the rear of the front bearing) and the rear bearing diameter.

The spindle has the 1/2" fit into the rear bearing, plus back of bit to back of front flange.

The bits have OAL plus the clearance angle plus the size of the bit hex.


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## ttabbal (Jun 25, 2021)

GunsOfNavarone said:


> What steel did you use



Not sure. I don't have any way to test it. I got the bearing pocket in, broke the edges and decided to take a break. There's a fair amount of metal to remove from the front, and the threaded holes.


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## ttabbal (Jun 26, 2021)

Mounting to a mandrel seemed to help keep space around the flange. After a few passes, I found some good settings for roughing this material and was peeling about 0.90/pass off. 






Hmmm.. Finish looks worse on the pics than in person. Can barely feel a few ridges with a fingernail.


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## ttabbal (Jun 26, 2021)

After drilling and tapping the holes, I use the lathe to run some emry over the back flange. It cleaned up nicely without much work. 

I spent some time with calipers and mics and everything looks great. Guess I need to make a few copies now.


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## GunsOfNavarone (Jun 26, 2021)

That's awesome! I was wondering, do we all send our part to Erich...for assembly, make sure all is well? Or just hail Mary it?


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## ErichKeane (Jun 26, 2021)

GunsOfNavarone said:


> That's awesome! I was wondering, do we all send our part to Erich...for assembly, make sure all is well? Or just hail Mary it?


That is what the other projects do, saves everyone a bit on shipping that way. And the hope is I could choose the ones that suffer the least from tolerance stacking.

Doesn't have to be me of course.


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## GunsOfNavarone (Jun 26, 2021)

@ErichKeane    You're probably past this point, but take a look at this this video.. by using compound, did they pull off the front (cupped area?)


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## ErichKeane (Jun 26, 2021)

GunsOfNavarone said:


> @ErichKeane    You're probably past this point, but take a look at this this video.. by using compound, did they pull off the front (cupped area?)


Haven't actually started yet! You guys are going too fast I'm still working on my dividing head parts!  I'll watch that though!


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## ErichKeane (Jun 26, 2021)

GunsOfNavarone said:


> @ErichKeane    You're probably past this point, but take a look at this this video.. by using compound, did they pull off the front (cupped area?)


Huh really interesting! I had actually been considering that a bunch lately, wondering if I could use some of my brazed carbide tooling plus the compound to cut the cupped area.

I hadn't thought about actually cutting the profile that way though, that is a really good idea! I can probably save my surface grinder a lot of grinding that way


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## ttabbal (Jun 26, 2021)

ErichKeane said:


> That is what the other projects do, saves everyone a bit on shipping that way. And the hope is I could choose the ones that suffer the least from tolerance stacking.
> 
> Doesn't have to be me of course.




Seems like a reasonable way to do it. I'm happy to send to whoever. Whatever works. I think you might be a good choice since you did the drawings and likely understand the way tolerances will stack more than we will, but I'll give it a go if you prefer. I've still got a few more to make before it's an issue for me. 

I'm interested in seeing more parts getting made as everyone gets time to do it, please post a pic or two. I think I need to do one before I clean up after doing the big material removal step. It makes a hell of a mess.  

Looks like we're making 4 total units? That's what I'll plan for unless someone says otherwise.


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## ErichKeane (Jun 26, 2021)

Yep, 4 total!  I don't mind any setup, just know I'm probably a bit behind all of you all   I haven't started up yet, I still have a bunch of dividing head parts to make.  That project got bit big/complicated (7 or 8 copies! AND I have to learn to hob gears), so I have a ton of turning to do.  Plus it just hit 110 today here in Oregon, so I'm off of shop time for a few days!


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## ttabbal (Jun 27, 2021)

No worries about timing. 

110 in Oregon? Wow. We've been close here in Utah, but you're further north. Even with a mini split and giant fan in the garage, I still have to shut down at that level.


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## GunsOfNavarone (Jun 28, 2021)

These kind of videos show up in my feed now…another interesting one. They have the angle at 1.8* and .067” off center. Not sure if it’s ration wise the same as ours. Interesting as well how critical the tool OAL is. As I have never used one…it’s taken a while to get the ins/outs and why if the tool.
I made a 2nd plate, this one dead nuts on 1* No sine plate, no gauge blocks just backwards engineering….Another Broach


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## GunsOfNavarone (Jul 4, 2021)

Everyone still alive? How's things going? Any trials and tribulations? I just need to drill the 4 mounting holes and the one center drilled tapped hole and all four are done.


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## GunsOfNavarone (Jul 4, 2021)

Everyone still alive? How's things going? Any trials and tribulations? I just need to drill the 4 mounting holes and the one center drilled tapped hole and all four are done.


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## Flyinfool (Jul 4, 2021)

Oh man, I am getting Déjà vu


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## ttabbal (Jul 4, 2021)

Been out of town, but I will be getting back to it soon.


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## T Bredehoft (Jul 4, 2021)

I'm shipping my spindles to Erich tomorrow. He says no one else has finished.


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## GunsOfNavarone (Jul 4, 2021)

Yeah, I got about 70% done last week and seemed I was down to about 1 hour...maybe 2 hours left, so I dialed it back and have been doing other projects. I guess no real rush at this point.
Doesn't seem as there is much back n forth on this, but for what's it's worth...
I need to drill the body mounting holes square to the 1* angled side. I've been just contemplating how to go about that. Playing with the option of running them on the manual mill or the CNC (I have the CAM code ready to go.) Nothing really important, but would have been cool to discuss as a group. I guess what I was shooting for some months ago when I threw the idea out for the group project (dividing head was really the way I leaned) It was really geared towards to the newbs who never ran off blueprints, the challenge of many people making many parts at different time/places and having it come together and either work great, or the trouble shooting of what/why. Of course it would need some seasoned "machinist" to oversee.
Anyway...everything is experience, so there's that.


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## GunsOfNavarone (Jul 6, 2021)

So, just to keep you all in the loop.
I THOUGHT I was going to put the backing plates in the CNC mill, compensate for the angle, find center in the boss and do my drilling and tapping. We’ll, my drill bit chuck doesn’t go to as large of a drill bit (Q, .332”) so things took a turn for the complicated. I went back to lathe and pulled out the independent 4 jaw. (I hate this thing) Now instead of setting my part on the chuck and center my machine around it, I needed to center my part…big difference. I had to set the tilt AND find center. (Did I mention I hate the independent chuck) 
I will say it was great practice to the Nth degree with this thing. 2 are drilled and tapped and I’m working on the other 2 now.  The last step is the 4 holes offset for the .041” which I should be able to do on CNC since it’s only a .266” hole (clearance for a .250”) 
I suspect I should be able to shop the plates to Erich by the weekend. I’ll label the parts for the amount of seconds off from the 1*, as I stated before, I will take the one with the most error as I can remake the part easy enough. Maybe we can share experiences with the tools and see what’s better/worse etc…


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## GunsOfNavarone (Jul 6, 2021)

Put the flats on and I’m done….


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## GunsOfNavarone (Jul 6, 2021)

Sooooo maaaanyyy setups…..EVERY DAMN TIME…. Shimming against that damn 1* of tilt. ARRRGGGHH! Took like an hour to do 2 plates, 3/4” flat.
3 setups EACH on the lathe, one EACH on the CNC MILL, 1 setup EACH on the manual mill. Was there an easier way? I dunno.


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## ErichKeane (Jul 6, 2021)

GunsOfNavarone said:


> Sooooo maaaanyyy setups…..EVERY DAMN TIME…. Shimming against that damn 1* of tilt. ARRRGGGHH! Took like an hour to do 2 plates, 3/4” flat.
> 3 setups EACH on the lathe, one EACH on the CNC MILL, 1 setup EACH on the manual mill. Was there an easier way? I dunno.
> View attachment 371274


When designing it, I figured the 1st op was to turn the back , then drill/tap the center.

Then, op2 is on the mill to cut the flats. 

Op3 is to flip it over and put it on a sine bar in the mill vise, mill the front face, then drill the 4 holes with the DRO. The only "trick" there is figuring out how to find the "center", but I'm reasonably convinced an edge finder would have done the job.


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## GunsOfNavarone (Jul 6, 2021)

ErichKeane said:


> When designing it, I figured the 1st op was to turn the back , then drill/tap the center.
> 
> Then, op2 is on the mill to cut the flats.
> 
> Op3 is to flip it over and put it on a sine bar in the mill vise, mill the front face, then drill the 4 holes with the DRO. The only "trick" there is figuring out how to find the "center", but I'm reasonably convinced an edge finder would have done the job.


I thought about so many things…. Again, in my head, this whole agenda was to make us get off our butts and do things we may not do. It’s obvious not everyone is on board for that same agenda…but I’m sending my parts to you with good warning…I’m not a professional and this was a bit of a stretch for me. I had to work constantly compensating for “error”, which was new. I have no sine bar so I had to figure out how to do this without that.  I pushed myself for tighter tolerances (understanding some were a must) it was fun, but hopefully we’ll all discuss the final product rather than just being done when we get our broach.
How do I get (Erich’s) address without posting it here for the world?


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## ErichKeane (Jul 6, 2021)

Hopefully it will be ok! I messaged you my address.


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## ErichKeane (Jul 7, 2021)

So I got a really slow step 1 done today: cutting the 6" HSS M2 blanks down to rough size.

Unfortunately the braized carbide inserts I have just wouldn't cut it! I tried a simple facing operation and it busted the carbide and chewed up the HSS.

I guess I'll have to spend more time researching how to make this cut.  I would not bother and do everything in the grinder, except this was my plan for the "dished" center.


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## rwm (Jul 7, 2021)

HSS M2 sounds like a tough choice. I made my broaches out of O1. Then again, I would not trust them to last long on harder alloys. And- resharpening broaches is problematic since it reduces the OD of the cutting edge no matter how you do it.
Guns-nice looking surface finish on those parts.
Robert


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## ErichKeane (Jul 7, 2021)

rwm said:


> HSS M2 sounds like a tough choice. I made my broaches out of O1. Then again, I would not trust them to last long on harder alloys. And- resharpening broaches is problematic since it reduces the OD of the cutting edge no matter how you do it.
> Guns-nice looking surface finish on those parts.
> Robert


Yeah, I was hoping to make the best possible cutters I could, since they are so expensive otherwise. I'm a bit curious how I'm going to make this happen now though...


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## GunsOfNavarone (Jul 7, 2021)

Yeah, that's rough. What's the answer? Whatever Robert was talking about?? I have two 12mm x 100mm round bars of HSS...but I believe you were using .500" diameter? Poop on a doorstep......


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## ErichKeane (Jul 7, 2021)

GunsOfNavarone said:


> Yeah, that's rough. What's the answer? Whatever Robert was talking about?? I have two 12mm x 100mm round bars of HSS...but I believe you were using .500" diameter? Poop on a doorstep......


Yeah, they are .500".  I HAVE the material (and cut to rough size!), but I just have to figure out how to cut them on the lathe..  I seem to see that I could get some types of inserts that will cut it with little problem, but I haven't been able to make heads/tails about them.  I guess worst-case I can try to make the dish on the grinder in some way...


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## GunsOfNavarone (Jul 7, 2021)

I saw you have the stock....but I was picking up that it y be of a kryptonite mixture...
This is for anyone that may come across this thread way in the future... This adjustment seems to simplify the whole centering issues... just food for thought.


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## rwm (Jul 7, 2021)

Earlier in the thread I was asking about having all the broaches the same length so that you could use the fixed 1 deg angle and not have to adjust the offset if you change broaches. The issue I ran into was grinding all the broaches to the correct OD without adjusting the length. In the end, I ground the broaches slightly oversize and then sharpened them (shortening them) to get the OD correct. That resulted in all my broaches being different lengths. Using a surface grinder may obviate this issue for you . Just some food for thought.
Robert


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## brino (Jul 7, 2021)

ErichKeane said:


> I guess I'll have to spend more time researching how to make this cut. I would not bother and do everything in the grinder, except this was my plan for the "dished" center.





ErichKeane said:


> Yeah, I was hoping to make the best possible cutters I could, since they are so expensive otherwise. I'm a bit curious how I'm going to make this happen now though...



Hi Guys,

I've been paying attention to rotary broach stuff for a few years with the very distant plan of building one.
That's why I've been following along here .....research.
However I did not join in your fun due to lack of time.

I do remember reading a paper saying that the concave end was not required and might even hurt cutting edge strength/life.
I will see if I still have a copy of that report.

I also remember someone cutting the dish shape with a dremel grinding stone with the broach cutter in a spindex.

-brino


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## rwm (Jul 7, 2021)

I cut my dish with a Dremel mounted on the cross slide with a cutoff wheel. I rotated the broach slowly in the lathe.
Robert


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## ErichKeane (Jul 7, 2021)

brino said:


> Hi Guys,
> 
> I've been paying attention to rotary broach stuff for a few years with the very distant plan of building one.
> That's why I've been following along here .....research.
> ...


I have a air-die grinder I think that i have some small wheels for, I might end up using those if that is necessary.  

A big part of it was trying to get the general profile 'right' to avoid spending too much time on the surface grinder, since that is likely going to take a while.  It would be interesting if I could skip doing the dish though!


rwm said:


> Earlier in the thread I was asking about having all the broaches the same length so that you could use the fixed 1 deg angle and not have to adjust the offset if you change broaches. The issue I ran into was grinding all the broaches to the correct OD without adjusting the length. In the end, I ground the broaches slightly oversize and then sharpened them (shortening them) to get the OD correct. That resulted in all my broaches being different lengths. Using a surface grinder may obviate this issue for you . Just some food for thought.
> Robert



I think with the amount of 'wobble' we have in ours that the offset is actually going to be less important than with other designs.  I suspect we'll have pretty close to a 'self adjusting' head, since the rear bearing fit is going to be so loose I think.


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## GunsOfNavarone (Jul 7, 2021)

Well. @ttabbal and myself will be waiting by the swim up bar, come find us when you guys are done!


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## ErichKeane (Jul 9, 2021)

Parts showed up today! The spindles showed up and are all great! The rear-most diameter might be troublesome, the extra is undersized by a bit, but hopefully still useable.

The rest are unfortunately tight on the bearings! I don't know if the bearings are just undersized, or I speced it out poorly. I figure I can chuck it up in the lathe to polish off a few thou to  make it a slip-fit.

Anyway, progress made! Great job @T Bredehoft !


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## ttabbal (Jul 9, 2021)

Nice to see more parts!!  I'll be getting some shop time over the next week, so mine will ship out soon. Hopefully temps will drop under 100F, but I'll work at night if needed.


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## GunsOfNavarone (Jul 9, 2021)

I’m hitting post office tomorrow, you should have the backing plates Tuesday-ish.


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## ErichKeane (Jul 9, 2021)

GunsOfNavarone said:


> I’m hitting post office tomorrow, you should have the backing plates Tuesday-ish.


Haha, wow! You guys are moving quick! I spent a bit of time already grinding 1 side if each but square to give me a reference surface. I'm still thinking through some order of operations, but this part went pretty quick! I have quite a bit ir material to take off a few length wise, but I think I can use the bench grinder to make up some distance quicky.


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## GunsOfNavarone (Jul 10, 2021)

I contacted that "TomMakeHere" guy....(one of the videos in this thread). He has an Etsy page and he normally offers 10mm diameter cutters, though he could do larger, he says he's having a problem sourcing the stock as of late. Anyone have a good source for these?


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## ErichKeane (Jul 10, 2021)

GunsOfNavarone said:


> I contacted that "TomMakeHere" guy....(one of the videos in this thread). He has an Etsy page and he normally offers 10mm diameter cutters, though he could do larger, he says he's having a problem sourcing the stock as of late. Anyone have a good source for these?


For the stock? I just got it on McMaster. 

For the cutters, polygon solutions https://www.polygonsolutions.com/

Is the best price I found, but McMaster has them too (though pricey).


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## ErichKeane (Jul 10, 2021)

Also... There's no reason you couldn't make an adapter sleeve from his 10mm broaches to the 1/2" broaches. That is a 50 thou wall. Shimming the length to be right, or adjusting the offset (might require slotting the backing plate) should be doable as well


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## brino (Jul 10, 2021)

brino said:


> I do remember reading a paper saying that the concave end was not required and might even hurt cutting edge strength/life.
> I will see if I still have a copy of that report.



Sorry guys, I looked but could not find that reference; either locally or on the 'net.

-brino


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## GunsOfNavarone (Jul 10, 2021)

Maybe this is completely ridiculous, but what about vandium steel hex drivers? If they were concaved on the front edge with a grinder/dremel, it would sharpen them...would this work? I'm talking for future use, expanding options like torx driver etc....


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## ErichKeane (Jul 10, 2021)

GunsOfNavarone said:


> Maybe this is completely ridiculous, but what about vandium steel hex drivers? If they were concaved on the front edge with a grinder/dremel, it would sharpen them...would this work? I'm talking for future use, expanding options like torx driver etc....


I think the problem is you still need to do the 'side relief' for the bits.  so unless the bits were cone-shaped (or so!) I don't see how that would work.  It MIGHT still cut on softer materials, but it would likely get stuck/break off pretty quickly.


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## GunsOfNavarone (Jul 11, 2021)

Awe yeah.... I guess there is no easy way out. 
How's @T Bredehoft coming along? Don't think I've seen him on here for a while?


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## ErichKeane (Jul 11, 2021)

@T Bredehoft sent me all the spindles already! See #216.


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## T Bredehoft (Jul 11, 2021)

I guess I'm waiting for everyone else. My share was not difficult, just a bit of lathe work. 

Tom


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## ttabbal (Jul 12, 2021)

Second part has all the turning done. The only thing left on it is the 4 tapped holes. The other two blanks are ready to go in the lathe. Taking a while to make them, but I'm likely being over cautious on dimensions and making sure they are cool before the final pass and measuring is done.


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## ttabbal (Jul 13, 2021)

Parts! 
	

		
			
		

		
	




Gotta get some packaging material and get them ready for shipping.


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## ErichKeane (Jul 13, 2021)

Gorgeous!  I'll make sure to send you my address.


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## ErichKeane (Jul 21, 2021)

I just got t tabbal's parts in today, which makes a complete broach holder! I still have to pick up the bolts and set screws to assemble, and do a slight rework on the spindle(as previously mentioned), but everything else looks great!

I'm really happy about how nice of a fit the spindle and body have, the .750 clearance hole works nicer if they are somewhar tight.



I've been delayed a bunch more on the bits, I ended up spending the last week or so buying then picking up, then playing with a new full-sized mill (plus spending this coming weekend moving it into place), so I have been distracted 

I DID spend some of my shop time today grinding the setscrew flat on the bits, though so far this cost me a grinding wheel! Believe it or not this wheel used to barely fit in the housing!



Fortunately I have one better at cutting HSS in the mail that I should be able to use to accurately cut the design on the broach.

And here they all are so far:


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## GunsOfNavarone (Jul 21, 2021)

Oh crap! forgot I had a broaching tool coming...I better find that arbor(s) I need! What size if the arbor on that grinder? What mill did you get?
On an somewhat related note...my compound machining project won me a new Mitutoyo Digital micrometer from Practical Machinist. I guess I got t post more of my projects, could be a lucrative side gig!


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## ErichKeane (Jul 21, 2021)

GunsOfNavarone said:


> Oh crap! forgot I had a broaching tool coming...I better find that arbor(s) I need! What size if the arbor on that grinder? What mill did you get?
> On an somewhat related note...my compound machining project won me a new Mitutoyo Digital caliper from Practical Machinist. I guess I got t post more of my projects, could be a lucrative side gig!


  You unfortunately have a little time, I probably won't be done with my parts and putting these together for a few weeks:/

The grinder uses 1-1/4" center hole grinding wheel, but I don't remember the arbor. It is some taper that is common to surface grinders.

I ended up getting a Bridgeport Clone by Birmingham, its a 10x54 table with a variable speed head and a 3HP motor!  Its a beast compared to my old machine!

Thats pretty awesome about the caliper too!  I didn't see that project, but it must have been a pretty nice one!  I tend not to be on PM, they seem to have an irrational hatred for shapers, and I have an even less rational love for them


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## ErichKeane (Jul 22, 2021)

Got my wheel in today and started grinding! Took about 2 hrs, but I got the first too bits ground well enough for their shape. These are 3/8" hex broaches, which were for ttabbal and myself, which I did since the biggest ones required less material removal and thus were easier!

I ground them at a 2 degree angle, so we should have plenty of clearance.

For the sizes I have:
T Bredehoft: 3/16, 5/32, and 1/8 hex
Ttabbal/myself: 3/8, 3/16 hex, 1/4" square 
GunsofNaravone: 3,4,5mm hex 
I still need to grind the inside relief on these, but 2 of 12 otherwise done


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## ErichKeane (Jul 22, 2021)

I did 5mm as well (took an hour for itself even though I felt like I was cruising) but I found that the "depth" of the 3rd cut was tough to measure, so the hex might not be centered right  it mics out pretty close on my surface plate, so perhaps it just looks worse than it is?

I'm going to have to figure out how to solve this for the smaller ones though.


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## T Bredehoft (Jul 22, 2021)

My broaches  don't need to be more than 2 diameters long....


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## ErichKeane (Jul 22, 2021)

T Bredehoft said:


> My broaches  don't need to be more than 2 diameters long....


Yeah I might shorten the depth of cut on the smaller ones, it at least should prevent the root from getting so small.


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## ErichKeane (Jul 23, 2021)

So I decided that I didn't like how the 5mm turned out, so I changed my strategy/setup. I took out the angle block and replaced it with a magnetic sine vise. This takes significant amount more time for my cycles, but is way more repeatable. I decided  I would do 1 complete set of cuts (6) as a roughing pass, dress my wheel and go around another time to get a size reading, then 1 more time to final size.

I did the post-wheel dressing part on the 5mm to make it a 4mm, then started on a replacement 5mm. Sadly the part rotated on me during one of the cuts, and I didn't notice until it wasn't savable. So, 1 in the trash :/




I restarted the 5mm and this one went way better, other than taking about 2x the time as the previous ones.   You'll note that the 5mm I also shortened how long the cutter is ground, hopefully this will strengthen it.  The 5mm->4mm conversion I didn't have this option, so it is still full depth.

I measured the two 3/8 cutters, and 1 is pretty close to right, the other is a little rough. I think I'll just keep the rough one to myself.

That said, this step is seemingly taking a while  I have 8 more cutters to go to get you all 3 of them (barring disaster or another mess up), and I likely will be doing 1x a day at this rate!


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## GunsOfNavarone (Jul 23, 2021)

Remember...I'm flexible on sizes...if the smaller of them are very time consuming for material removal, I can go with 3/8" and 1/4"...what evs...


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## rwm (Jul 23, 2021)

Would it more expeditious to take down the diameter on the lathe and then grid the remaining?
Robert


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## ErichKeane (Jul 23, 2021)

rwm said:


> Would it more expeditious to take down the diameter on the lathe and then grid the remaining?
> Robert


I had tried at one point but my brazed carbide tools chipped/broke almost immediately. It was my initial plan to use the lathe for that and the cup at the end, but it didn't work :/


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## rwm (Jul 23, 2021)

Got it.
I found this pic of dishing the end of the cutter:



Robert


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## ErichKeane (Jul 23, 2021)

rwm said:


> Got it.
> I found this pic of dishing the end of the cutter:
> View attachment 373203
> 
> ...


Yeah I'm probably stuck doing something like that at the end. I don't have a Dremel or anything so I might have pick one up.


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## GunsOfNavarone (Jul 23, 2021)

The blanks are HSS....correct? That's crazy! Now I guess I se why finished cutters are so damn expensive. Seems like if (they) had a CNC rotary table mounted to a grinder they could knock these things out, but obviously there isn't a whole lot you can do to as a hobbyist.


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## ErichKeane (Jul 23, 2021)

GunsOfNavarone said:


> The blanks are HSS....correct? That's crazy! Now I guess I se why finished cutters are so damn expensive. Seems like if (they) had a CNC rotary table mounted to a grinder they could knock these things out, but obviously there isn't a whole lot you can do to as a hobbyist.


Yep, pretty much! Most hobbiests seem to use O1 which even hardened is way softer, but they tend to wear when broaching steel.

I realized that I have a 2nd 5C collet set that I could probably set up to rough 2 cutters at a time, so perhaps ill try that!

I think I am running out of coolant for the grinder, so I gotta buy another bucket soon too.


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## brino (Jul 25, 2021)

A few thoughts from an interested observer......

1) O1 might be the way to go; certainly easier to cut, but then you need a hardening step too. It really depends on the expected life of the tool. How many holes would a hobbyist broach? For me it would be a small number. But this might vary widely by user.

2) I wonder if you could do some roughing to get it down in size some other way, saving the expensive surface grinder wheels for finishing.
What comes to my mind:

i) bench-top belt sander with the belts recommended by @mikey in that huge "sharpening HSS lathe tools" thread.
It could still be held in the hex collet block, although you may have to come up with a new fence arrangement, as with the collet block flat on the standard square table you'd be grinding 90 deg to that face. It would still produce a hex, but the flat faces on the part would be at the corners of the collet block. The way you're holding the collet block the surface grinder produces the flats on the part in the same plain as the collet block.
If you have a belt sander where the fence can be set accurately to 60 degrees then this should work.

ii) very crude, but even an angle grinder could be used to remove the bulk of the HSS material

Great thread, I am routing for you!

-brino

EDIT: wait there is an easier way to align the roughing cuts on a belt sander with the finish cuts on the surface grinder..... just hold the collet block by the flats instead of the points in the SG vise.


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## GunsOfNavarone (Jul 25, 2021)

Yeah, those bits are more of a bear than I imagined. As I don't own anything accurate like a surface grinder...I will never attempt this at home, I will be buying mine ready made if and when I find myself in need..


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## ErichKeane (Jul 26, 2021)

So, a lot of progress today! First, I decided to get the broaches assembled!  There was a little bit of repair to each component necessary, but nothing too bad.

I started with the spindle. The tail was a little oversized, so a little bit of time with a file and some Emory paper made the bearings fit:




Next I looked at the body parts. The bearing fit in nicely, though some deburr process seemed to make a couple of the threaded holes not really work. The 10-32 were the worst (3 of them wouldn't start), but the 1/4-28 had a pair as well. A few minutes cleaning up with a tap made short work of all of these however.




And here is a little layout of how the assembly works. Spindle, thrust bearing/washers, body, bearing, cir-clip.




A little bit of the tapping repair 



Spindle and thrust bearing in the bodies:



Then bearings:




Then cir-clip/snap ring or whatever these are called 



Next, to the backing plate. 3 of the 4 were fine, but all 4 holes in the other had some weird "step" inside that prevents the bolt from getting through the hole.  I used a drill to finish these holes, no problem 



And here is the group picture all bolted together!




Next, I got back to my bits. I opted to work on the 1/4" square to try my new strategy of first hand grinding. I marked out the ends with blue and a height guage which got me rough measurements.  I ended up getting down to .325 manually;



Then a bit of back and forth on the surface grinder got them just right!
	

		
			
		

		
	




And a picture of all the bits so far!
I have a 4 and 5mm ground, 2 3/8, and 2 1/4 square. I still have to grind the cup end in them, but 6 of 11 at least precision ground (plus the one screw up last week!).


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## GunsOfNavarone (Jul 26, 2021)

I bet I know the step on the one backing plate...it was the 1st one I drilled and my setup was questionable for the survival of my vice. The bit broke through, but not by a lot. I chamfered the edge, but I bet it left a bit of a wall. The other 3 I learned and changed my setup.
And going back to the original thread "This Madness needs to Stop", this is one of the interesting parts. When all these parts, made by different people, with varying skills on different equipment, comes together. Is it just me? I mean, I know I take it for granted if I order a intake manifold and bolt it to my block....it fits. It's much different when it was a shapeless piece of stock in your hands. I dunno....goose pimple material.


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## ErichKeane (Jul 26, 2021)

GunsOfNavarone said:


> I bet I know the step on the one backing plate...it was the 1st one I drilled and my setup was questionable for the survival of my vice. The bit broke through, but not by a lot. I chamfered the edge, but I bet it left a bit of a wall. The other 3 I learned and changed my setup.
> And going back to the original thread "This Madness needs to Stop", this is one of the interesting parts. When all these parts, made by different people, with varying skills on different equipment, comes together. Is it just me? I mean, I know I take it for granted if I order a intake manifold and bolt it to my block....it fits. It's much different when it was a shapeless piece of stock in your hands. I dunno....goose pimple material.


Ah, that might be it  

Yeah, I'm REALLY amazed at how easily everything went together! I really thought I was going to have to put SOME part on the lathe in the 4 jaw and cut more to make the bearing fit, but it was a slip fit on the OD, and easily enough to get to fit on the ID!

The lengths/sizes/bolt holes/etc ALL seem to work!  I'm really impressed with what you three were able to do!  Hopefully in another week or two I'll be ready to start shipping out complete sets!  Perhaps not all 3, but at least one


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## ttabbal (Jul 26, 2021)

Nice to see parts fitting together nicely! Particularly from multiple people on who knows what equipment. Great job everyone!


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## rwm (Jul 27, 2021)

Eric-Sounds like you have your grinding technique down! The broaches look great. I may try to enlist you to make one for my holder!
Robert


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## ErichKeane (Jul 28, 2021)

Only had an hour today but decided to see if the Chinese inserts I found on ebay would survive. First test cut looked promising so I decided to try roughing some of the smaller ones this way.

This was HARD on the cutters, and broke them almost immediately. However, most of the time they broke with a decent cutting edge, so, I sent it . 3 bits cost me 4 cutting edges (2 per cutter), but hopefully saved me a bunch of time.

I have 2more left to rough out, so I think I'll do it this way! Hopefully I can find a cutting speed that doesn't murder these and can use it on the end profiles.


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## GunsOfNavarone (Jul 28, 2021)

If it saves time.....it's worth it! Nice work


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## ErichKeane (Jul 29, 2021)

Hmmm... No progress today! My electric mag chuck seemingly is kicking off my GFCI as soon as I hook it up.

It's strange, it worked fine for a long time, switching out the bridge rectifier didn't change anything, and it only happens when everything is wired up. It also doesn't show any shorts or anything.

Guess I get to spend some time figuring out why this happens :/


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## Mheaton92 (Jul 30, 2021)

How do you get in on a group project? Do you just have to notice when one starts?


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## ErichKeane (Jul 30, 2021)

Mheaton92 said:


> How do you get in on a group project? Do you just have to notice when one starts?


Yep pretty much. I think the dividing head has some unclaimed parts, but not sure how many people could make another.

You could always come up with something and organize one! The dividing head shows that complicated ones take a while(if they finish!) and I think the clamps were perhaps not complicated enough to get interest to finish.  I think this rotary broach ended up being just a out perfect for both!  Only downside is needing one person who can grind the bits.


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## Weldingrod1 (Jul 30, 2021)

We need another person on the sliding bar clamp build ;-)

Hint, hint...

Sent from my SM-G892A using Tapatalk


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## Mheaton92 (Aug 1, 2021)

ErichKeane said:


> Yep pretty much. I think the dividing head has some unclaimed parts, but not sure how many people could make another.
> 
> You could always come up with something and organize one! The dividing head shows that complicated ones take a while(if they finish!) and I think the clamps were perhaps not complicated enough to get interest to finish.  I think this rotary broach ended up being just a out perfect for both!  Only downside is needing one person who can grind the bits.


I think I will try to organize one. I am trying to help with the clamps, but I agree 100%. I didn't want to do the clamps, they didnt seem like a lot of fun because of the simple design. That being said, I will still get in on it. This broach looks awesome, I will one day buy a surface grinder and when I do this build will be first on my list!


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## ErichKeane (Aug 1, 2021)

Mheaton92 said:


> I think I will try to organize one. I am trying to help with the clamps, but I agree 100%. I didn't want to do the clamps, they didnt seem like a lot of fun because of the simple design. That being said, I will still get in on it. This broach looks awesome, I will one day buy a surface grinder and when I do this build will be first on my list!


Fortunately I designed this around commercially available bits, so you can get them from McMaster and a few other places! They are costly ($50-$100 each!) , but at least obtainable.


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## Mheaton92 (Aug 1, 2021)

ErichKeane said:


> Fortunately I designed this around commercially available bits, so you can get them from McMaster and a few other places! They are costly ($50-$100 each!) , but at least obtainable.


ok cool, I am sure everyone on this forum is just like me and has 100 projects going at once. So it will go on the list. I was in the middle of building a model engine and decided to make a solid tool post. So once the tool post is done I will go back to the engine then onto this now!


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## Weldingrod1 (Aug 2, 2021)

Hey, so recent hard won lesson... you -must- have a chamfer to get the broach started. If you bore.a shoulder in that is a close fit on the broach, it will not start. It will push a ring of material in :-(

Sent from my SM-G892A using Tapatalk


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## ErichKeane (Aug 2, 2021)

Got the outer dimension of all the cutters ground. 11 successes out if 12!

I still have no idea how I'm going to cut the cup in the end. A few of them are incredibly tiny, so I have no idea how to get that to happen with a grinding wheel...


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## ttabbal (Aug 2, 2021)

For the little ones, maybe something like a dremmel with a grinding stone?


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## ErichKeane (Aug 2, 2021)

ttabbal said:


> For the little ones, maybe something like a dremmel with a grinding stone?


I ordered a Dremel knock off that I'm going to try to clamp to my tool post or something... Best idea I have. You can't use anything other than a thin disk, otherwise they just end up being flat!


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## GunsOfNavarone (Aug 2, 2021)

I could grind my own cups if that helps. I have a flexible shaft grinder...think it's like 10hp! ; )


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## ErichKeane (Aug 2, 2021)

GunsOfNavarone said:


> I could grind my own cups if that helps. I have a flexible shaft grinder...think it's like 10hp! ; )


I'm going to try on the two that are for me first, if they don't work, I might just send everyone's to you    I ordered a cheap dremel clone that I am going to try to use on the lathe with some grinding wheels, so we'll see!


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## ErichKeane (Aug 3, 2021)

I found a couple of affordable broaches on ebay for anyone who is interested:
7/32" : https://ebay.us/WhtO3P  Looks like this guy has a bunch of them!
5/32" https://ebay.us/fzG17a Same guy, same deal!

These are somewhat common allen wrench sizes, so I suspect some of you might find them useful, partiuclarly since they are only $35 each, significantly cheaper than these usually go for.


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## John O (Aug 3, 2021)

Is the cup needed? I saw an article where they didn't put the cup and it cut the same.


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## ErichKeane (Aug 3, 2021)

John O said:


> Is the cup needed? I saw an article where they didn't put the cup and it cut the same.


Do you have a link to that article?  Someone mentioned it above, but thought they were mistaken.  I would LOVE to not have to do the cup


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## ErichKeane (Aug 3, 2021)

@ttabbal @T Bredehoft @GunsOfNavarone 

PM me your addresses and I can ship out your stuff!  I can try cupping the bits first if you'd like, but if @John O has an article that says it doesn't make a difference, I'm just as up for not doing it.  Let me know in PM if you want it ASAP, or to wait for my attempt to cup them.


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## brino (Aug 3, 2021)

John O said:


> Is the cup needed? I saw an article where they didn't put the cup and it cut the same.



@John O , if you can find that reference we would all be interested.



ErichKeane said:


> Someone mentioned it above, but thought they were mistaken. I would LOVE to not have to do the cup



Actually I believe that I mentioned it first in post #212.
I went searching for the article and never found it. I mentioned that in post #223.

The idea was that the cutting edge was stronger with a flat face.

The only reference I can find now is this quote:


> Most sources suggest a concave end, randyc indicated that a flat grind will remain sharp longer than concave.



from here:
http://jamesriser.com/Machinery/RotaryBroach/Build.html

-brino


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## ErichKeane (Aug 3, 2021)

>>Most sources suggest a concave end, randyc indicated that a flat grind will remain sharp longer than concave.        

This matches my expectations.  A flat face will have a 1 degree cutting rake, so it at least will 'cut', though perhaps a larger rake is beneficial for cutting?  Either way, a flat face will wear better I suspect.


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## ErichKeane (Aug 3, 2021)

@ttabbal and @T Bredehoft : both shipped USPS a minute ago, should be there Friday!


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## T Bredehoft (Aug 3, 2021)

Great. and thanks for the experience...


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## ErichKeane (Aug 3, 2021)

All 3 shipped! Everyone should get it Friday!


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## GunsOfNavarone (Aug 3, 2021)

Man! wasted NO TIME shipping those.....I don't blame you at this point, I think you bit off a big job...


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## ErichKeane (Aug 3, 2021)

GunsOfNavarone said:


> Man! wasted NO TIME shipping those.....I don't blame you at this point, I think you bit off a big job...


Hah, I am glad to have it off my plate... Next time I'll take an easier part 

Fortunately you sent me your info about 20 mins before the post office closes, so I was able to go down the road and get out of my hands!


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## ttabbal (Aug 3, 2021)

Cool! Looking forward to checking it out.


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## John O (Aug 3, 2021)

ErichKeane said:


> Do you have a link to that article?  Someone mentioned it above, but thought they were mistaken.  I would LOVE to not have to do the cup


Sorry, don't remember where, it was more than 10 minutes ago


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## Winegrower (Aug 4, 2021)

John O said:


> Is the cup needed? I saw an article where they didn't put the cup and it cut the same.


I made a rotary broach for fun, and a 1/2” hex tool out of O-1, but did not harden it.   With a flat, not cupped, bottom, it had no trouble punching a hole in (as I recall) 1/8” aluminum.   it worked surprisingly fast, looked none the worse for wear, and then I put it in a drawer, have not used it since.  I did post on this, if anyone is interested.


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## GunsOfNavarone (Aug 5, 2021)

Now that this is over.... this tool post mounted version looks pretty awesome.
Tool post broach


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## ErichKeane (Aug 5, 2021)

GunsOfNavarone said:


> Now that this is over.... this tool post mounted version looks pretty awesome.
> Tool post broach


I think i saw the video on that one at one point!  I think it is pretty cool how simple he was able to make it, though I think we chose to do bearings to avoid wear.

I also don't really see the advantage of putting it on the tool post vs the tailstock.  I would think you'd spend a ton of time 'centering' the broach with the carriage, both up and in.  I'm sure it is useful, it just seems less practical.


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## ttabbal (Aug 5, 2021)

Got mine in today. It looks great on the bench! Unfortunately, I neglected to order an arbor until the last minute, so I can't give it a try, but that's alright. If I decide to be in a hurry, I can make a straight shank real quick on the lathe, but I suspect the one I ordered will get here before I get shop time to make one.  

I need to look up how to use these things again. But it looks like I can use the set screw in the front to swap cutters, then it should work like any other rotary broach, right?


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## ErichKeane (Aug 5, 2021)

Ye


ttabbal said:


> Got mine in today. It looks great on the bench! Unfortunately, I neglected to order an arbor until the last minute, so I can't give it a try, but that's alright. If I decide to be in a hurry, I can make a straight shank real quick on the lathe, but I suspect the one I ordered will get here before I get shop time to make one.
> 
> I need to look up how to use these things again. But it looks like I can use the set screw in the front to swap cutters, then it should work like any other rotary broach, right?


Yep this is a traditional rotary broach.

The key is that you predrill a few percent over the flat-diameter, then add a champher larger than the OD to lead the cutter in, the rotate the broach into the material (or rotate the material into the cutter).


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## GunsOfNavarone (Aug 5, 2021)

I feel ya @ttabbal  I ordered my arbor last night. I can't say I have any immediate plans for it....it was more the experience. Been welding in a hot shop all day....too burnt out to even go check the mail! I kinda let the instructions how to set these up prior to cutting (center it/off center it) go in one ear/out the other. Do you use an indicator?? Damn my short attention span!!


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## rwm (Aug 14, 2021)

I hope we will see some video of this in action?!
Robert


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## T Bredehoft (Aug 14, 2021)

I clamped a dumore grinder with a 3/8 spherical stone to my tool post, put the cutters in the 1/2 collet, spun both up to speed and within seconds had concave grinds in the hex cutters.

No big deal. I know, no pictures, it didn't happen, Pix on my cell phone, won't send to me, dumb cell phone.

_Edit:_ correct typo


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## GunsOfNavarone (Aug 14, 2021)

I’ll try to soon. Just got my arbor yesterday but I have  a couple projects going on right now (your  eagle 66 is one of them!) @rwm


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## GunsOfNavarone (Aug 17, 2021)

So….I’ve never used one before, and this where I’ll ask how to set the offset…didn’t have great luck with 12L14 steel, but again, first time. Went to aluminum and it worked! I used the 3/8” bit which might be a bit small. I ran it a 2bd time with the hex in a different position and I could JUST force an Allen in.


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## GunsOfNavarone (Aug 17, 2021)

Rotary broach first shot
					






					youtube.com


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## GunsOfNavarone (Aug 17, 2021)

First run Rotary broach
					






					youtube.com


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## ErichKeane (Aug 17, 2021)

It looks like from the picture you did it right. If the 12l14 didn't work, perhaps the hole needs to be a touch larger? Or the chamfer?

I ground the cutters to the values on the paragon website, but those were perhaps too small  if you rotated it and did better, I might not have ground that one perfectly even, I know the 3/8" ones were the first I ground, so perhaps the least consistent.


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