# Small face mill using tangential cutter



## homebrewed

I recently made a small face mill that uses a 3/16" diameter HSS rod for the cutter.  The idea was to replace an indexable face mill with something that would handle interrupted cuts better (I always seem to chip the inserts).  I like the concept of the tangential cutter because they're dead easy to sharpen.  To simplify some of the machining steps I made the face mill in two parts -- the arbor and the holder for the cutter.  I started with a 3/4" rod of HRS for the arbor and some 1.25" diameter 4140 for the holder.  The photos below show a few steps in the process of making it, after I did the initial lathe work to turn the 3/4" rod down to 11/16" to fit my R8 collet and smoothed/faced the holder down to a .486" thick disk (there was no specific thickness target, it just ended up that thick).

This photo shows the holder in my angle vise.  The vise is set to 12 degrees from horizontal, and I'm milling a flat preliiminary to drilling the 3/16" hole for my HSS rod.
The slot (machined in a previous step) is .1" deep and .5" wide, and matches a tang milled on the end of my arbor.  With this approach the bolt that joins the two pieces doesn't have to resist the torque produced by the cutter when it's removing metal....and I can make different-sized holders as needed.  To make it easy to accurately rotate the holder 90 degrees, before breaking down the previous setup I also milled two flats on the side of the holder.  That gave me a nice secondary reference plane. 



The photo below shows the holder and arbor assembled to make sure they fit OK.  This photo actually predates the first one shown above.  My old drafting ruler is there to provide a sense of scale.  I was able to machine the slot and tang accurately enough to get a friction fit.  'Course, if I hadn't done so well I wouldn't have mentioned it .



Below shows the finished product, complete with a shortened hunk of HSS that's been ground to 30 degrees on the end.  I wrote a spreadsheet to calculate the offset necessary to place the tip of the cutter so it is exactly tangential to the circle swept out by the tool, when the cutter is projecting .1" below the bottom face of the holder.  I also used the same spreadsheet to determine where I needed to drill/tap the hole for the set screw.
After grinding the HSS I did notice a small burr on the end so I honed it with a 600 grit diamond file.  That produced an edge that would easily shave my fingernail.



Below shows the result when I tried my face mill on a piece of 6061.  I also tried it on some HRS with a .01" depth, full .75" wide cut and it worked just fine.  No chatter, nice smooth surface.  This was done on my Sieg SX2 mini mill, not the most powerful beast around, so I call it a success.
I was concerned that the cutting forces would push the cutter into the holder but that wasn't a problem.  Not so far, anyway....


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## frankly2

Nice work ! Proof is in the pudding ! The finish is very tasteful and looks excellent, nice design work !


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## homebrewed

Thanks for all the positive responses!

I have attached the spreadsheet I used to calculate the locations of the holes used to hold the cutter and set screw.  I tried to make the program as generic as possible so the design could easily be scaled up.  Downsizing it might be difficult, unless you also reduce the size of the arbor or drastically reduce the length of the HSS rod so it doesn't protrude through the top of the holder.  As it was, I had to reduce the length of the rod so I could grasp a decent length of the arbor in my R8 collet.  The piece I used is long enough to be resharpened quite a few times before I would need to replace it.  Another alternative I just thought of would be to make the holder thicker (taller), to accommodate a longer rod.


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## dian

not sure i get it. what part of the rod is the cutting edge?


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## homebrewed

Grinding the end of the rod at an angle produces an elliptical facet.  The cutting edge is the narrow end of the ellipse.  The relief angle(s) are produced by tilting the rod at a 12 degree angle and the 30 degree grind on the end of the rod.

The next-to-last photo in my original post shows the rod installed in the holder.

I'm thinking of making a holder for my lathe's QCTP to use a similar style of cutter.  It will be interesting to see how that performs, and the holder will be much easier to make compared to the tangential designs I've seen.  However, unlike the tangential designs it won't be able to turn to a square shoulder.


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## DavidR8

I really like this idea, great work.
Flycutters freak me out a bit as they whirl around looking unbalanced and ready to fly apart.




Sent from my iPhone using Tapatalk


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## Tozguy

Very imaginative and beautiful work.
Just to be sure I understand, with a 12 degree hole and a 30 degree grind on the end, relief at the cut would be 18 degrees?
What maximum depth of cut would you try on steel?
Please keep us posted on what you come up with for use on a lathe.
Thanks for sharing.


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## homebrewed

Tozguy said:


> Very imaginative and beautiful work.
> Just to be sure I understand, with a 12 degree hole and a 30 degree grind on the end, relief at the cut would be 18 degrees?
> What maximum depth of cut would you try on steel?
> Please keep us posted on what you come up with for use on a lathe.
> Thanks for sharing.


Yes, that's how the relief angles work out.  I tried a .01" depth of cut in some HRS and got a nice finish, with no complaints from the tool or mill.

It would be easy to try a grind angle less than 30 degrees (as long as it's at least 12 degrees).  I had thought of trying something like 20 degrees to get a more robust cutting edge....that is, if the 30 degrees turns out to be a little too fragile.  So far so good though.


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## homebrewed

DavidR8 said:


> I really like this idea, great work.
> Flycutters freak me out a bit as they whirl around looking unbalanced and ready to fly apart.
> 
> 
> 
> 
> Sent from my iPhone using Tapatalk


Thanks for the kind words!
I've got a flycutter as well but it really is too big for most of the stuff I do.  And like you I'm pretty paranoid about that big, unbalanced thing spinning around.  The tool I made is similar to a flycutter, in that it's a single cutter spinning 'round but much smaller and the geometry of the cutter itself is different.


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## dian

homebrewed said:


> "Grinding the end of the rod at an angle produces an elliptical facet.  The cutting edge is the narrow end of the ellipse.  The relief angle(s) are produced by tilting the rod at a 12 degree angle and the 30 degree grind on the end of the rod.
> 
> The next-to-last photo in my original post shows the rod installed in the holder."
> 
> thats what i figured. why then do you call it tangential?



o.k., maybe i get it now: the two angles are not in the same orientation. is the 12° from axis of rotation? but then the narrow end wouldnt be the cutting edge. on the pict. it looks like the angles line up (30-12=18°)

this is a cutter i made:





its originally for a radius attachement but it cuts and faces wery well.

(how to delete the second pict.?)


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## homebrewed

dian said:


> o.k., maybe i get it now: the two angles are not in the same orientation. is the 12° from axis of rotation? but then the narrow end wouldnt be the cutting edge. on the pict. it looks like the angles line up (30-12=18°)
> 
> this is a cutter i made:
> 
> View attachment 315875
> View attachment 315875
> 
> 
> its originally for a radius attachement but it cuts and faces wery well.
> 
> (how to delete the second pict.?)


Nice!  In regards to my remark on making something along the same lines, is the rod vertical or does it have a small forward (toward the headstock) tilt angle?  It's hard to tell from the photo.  Based on where the fixing screw is, I'm guessing it is vertical.  Altogether possible I'm wrong in that.


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## dian

yes, tilted 5° i think. i made another rod out of carbide that was concave on top and that was very good for parting off. i never use the contraption though.

so are your angles "paraller" or not?


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## homebrewed

dian said:


> so are your angles "paraller" or not?


Mathematically speaking, no.  But they have a specific relationship, and it's all relative to the plane of the work.  A drawing is easier to show the relationship.



In this side-view drawing, the horizontal black line is the plane of the workpiece.  The red lines show the cutter.  In this view, the plane of the ground facet also is a line.  So the relationship is as follows:  the plane defined by the facet _would_ be parallel to the workpiece if it was rotated 30 degrees counterclockwise around the tip of the cutter.

In this drawing the cutter will move from left to right as it removes material from the work.  That's probably backwards from how it works with a real tool rotating clockwise but the drawing was for purely pedagogical purposes 

It also can be seen from the drawing that the tip of the cutter will contact the work first, even if it's rotated around its own axis.  If this is done within reason, we'd have a cutter that cuts with some shearing action involved.  Of course, rotating it by more than +/- 90 wouldn't work.  Exactly 90 degrees might cut slots with square bottoms but my gut feel is that the cutting action would be pretty strange.  Now I've thought of that I guess I have to try it...


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## homebrewed

I have some follow-up results regarding the tool I made.  I noticed that the cutter dulled pretty quickly when machining steel so I made another grinding fixture that puts a 17 degree angle on the HSS rod, rather than 30 degrees.  The idea was to get a more-robust cutter by changing the included angle from 60 degrees to 73 degrees.  The holder geometry is the same, tilting the rod 12 degrees from the vertical.  As a result, the cutter has 5 degrees of back relief relative to the plane of the work.

I haven't tried the new cutter angle on steel, but it doesn't work all that well on aluminum, at least not on material that is wider than the cut path.  It sort of shears the aluminum, leaving a rough, raised edge.  Multiple passes across the entire surface work OK, but the strange cutting forces don't produce a very good surface finish.  I also can tell that the tool is working harder to make the cut.  I wasn't going for a high DOC, either -- .005" per pass.

I'll try rotating the cutter in the holder to different angles and see what happens.


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## Tim9

I made a similar flycutter and agree that getting the right cutting angle is a trial and error sort of thing. I played with various grinds before getting it about right. It’s still a work in progress because whenever I use it....I start farting with the cutter angle again.


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## homebrewed

Tim9 said:


> I made a similar flycutter and agree that getting the right cutting angle is a trial and error sort of thing. I played with various grinds before getting it about right. It’s still a work in progress because whenever I use it....I start farting with the cutter angle again.



Thanks for the feedback.  Your version looks quite similar to mine.  I do have a question regarding the cutter itself.  It looks like you ground a sort of hook or (for lack of a better word) chip breaker gullet into it.  Is that correct?

Also, I'm wondering if the flat you milled into the holder was done to improve the balance, or for some other reason.  I like the idea of improving the balance.

Thanks!


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## Tim9

Homebrewed. I apologize for such a long delayed response. I just totally missed that you had questions about my little cutter. 
So, here goes. Anyway I forget the birth of my cutter but FWIW, I used a 3/8” round HSS tool for my cutter. So I did put a curved grind on my cutter and it does seem to act as a chip breaker. I get a pretty nice finish when using it on aluminum. But I’m also taking fairly small cuts. And I’ve experimented with both the angle of attack of the cutter. My tool is still a work in progress every time I use it.


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## ThinWoodsman

Like the idea, especially using a round cutter, which should improve the finish like on some of the shaper and lathe tools.

It should be possible to modify a flycutter head to do this, correct? Drill a hole at the correct angle and add a set screw. I seem to have ended up with a gazillion* different fly cutter heads.

* That's machinist for _eight_.


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## Tim9

Yeah, I saw someone else's build where he used a round cutter. Just easier to drill that round hole than make a square one. But since its round, I did use two set screws. And yeah, just drill at the angle you want. All this said, the ones you see sold online tend to be pretty proven designs. Thats the ones like this. 

FLYCUTTER


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## middle.road

So, now I've got a question.
Could I take an existing fly cutter, bore a hole into it, add a couple of set screws and make a tangential cutter out of it?
Use a busted 1/4" end mill shank for the cutter perhaps?


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## ThinWoodsman

That's basically what I was thinking. I have a couple of fly cutters that are not sloped on the bottom liked the one Tim9 linked to, though the cheap sloped ones are most likely the ones I would sacrifice. Might be able to make a non-sloped (er, flat) one dual-purpose, though.


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## homebrewed

Some good discussion here!   Based on my experience with seeing how an apparently small change in the cutter profile can greatly alter its performance, all I can say is:  try your ideas and see how they work.

For now, I've gone back to my original cutter profile, it seems to be much more forgiving.  If I mill steel with it, I guess I'll just have to sharpen it more -- but that is really easy to do since it's just one facet.  Maybe an in-between angle is the sweet spot.  Also relatively easy to try.


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## savarin

I ground a round bit of tool steel, just ground to the angle that looked right. 
It was fixed into a chunk of flat steel that was held on the lathe face plate making a large dia fly cutter.








						Potd - Project Of The Day- What Did You Do In Your Shop Today?
					

:thinking:  Mark, what will you use a drill chuck on a live center for? :dunno:  That is a good question.:rofl:  Seriously , I used to think the same thing until I needed it. One  use is machining small work or doing machining on a bolt or screw. I had a hard time machining grooves in some SHCS...




					www.hobby-machinist.com
				



post 8028
This one just used a square bit but I also used a round bit for experimenting.
It was interesting rotating the tool bit so it contacted the work at different angles and some angles of attack produced very fine surface finishes reminiscent of a vertical shearing bit
https://gadgetbuilder.com/VerticalShearBit.html


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## Tim9

I did the same thing as you Savarin. It’s been a while, but I played around with it a while until I was taking really paper thin cuts of aluminum.
FWIW, .... Joe Pie has a good video on this subject of tweaking a flycutter


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## ThinWoodsman

savarin said:


> It was fixed into a chunk of flat steel that was held on the lathe face plate making a large dia fly cutter.



That reminds me of a "facing cutter" I saw the other night when re-reading the  George Thomas UPT book. His design has two cutters - for balance, presumably. Neat little cutter.


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## Tim9

Yep... that’s a great book. I forgot all about it .... And obviously misplaced it somewhere around my house. I have to look for it. He has a lot of interesting projects. Some dated, but some worth a look at in my opinion.


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## middle.road

Tim9 said:


> Yep... that’s a great book. I forgot all about it .... And obviously misplaced it somewhere around my house. I have to look for it. He has a lot of interesting projects. Some dated, but some worth a look at in my opinion.


FIND IT! Quick!
I just checked on amazon for it, $855.58


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## ThinWoodsman

Nah, tee press still publishes them for about forty bucks. https://www.teepublishing.co.uk/books/in-your-workshop/workshop-techniques/


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## Tim9

I thought I paid @65.00 for it. I do remember seeing some crazy prices for it but after a bit of searching I finally found it for @ 65. 00

But, the exchange rate was probably different. I just checked that link... and with shipping to USA... and Pounds to dollars, It comes to @ 53.00 now. 
anywho.... it’s a really interesting book with lots of great pictures of Harolds projects. And he goes into great detail with his descriptions. In any case, I know I can find it. It’s around and i will put my hand on it to take another look.  I do remember being thoroughly impressed with his dividing head build. Just beautiful workmanship.


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## courierdog

Homebrewed
Really enjoyed your article 
*Small Face Mill Using Tangential Cutter *








						Small face mill using tangential cutter
					

I recently made a small face mill that uses a 3/16" diameter HSS rod for the cutter.  The idea was to replace an indexable face mill with something that would handle interrupted cuts better (I always seem to chip the inserts).  I like the concept of the tangential cutter because they're dead...




					www.hobby-machinist.com
				



You have no idea how long I have been looking for someone to design a simple Tangential Fly Cutter
This design can be built to order to fit the size of the project.
As I am limited to things which can be done on an SX2 Mini-Mill as well.
I also got your Excel spreadsheet design as well many thanks.
This may be a very worthwhile mill project.
I love the single concept of the tangential cutter, I have the Diamond Tool Holders for my C4 Lathe and they work excellent. I spend a lot of time sharpening my tools using the Tormek. while the initial shape takes longer once in the final shape the it requires a touch up it is dead easy and they are super sharp and virtually burr free.
Now you have a challenge to build the same tool to cut the 0.5 inch slot for the arbor, which would also prove another point of it concept. ha ha
Great project and one of the first Fly cutters where someone actually took time to design a simple version which can be scaled to the task at hand. Using the Round Tool HHS Tool Steel Bit makes for an excellent finish. I sent a lot of time in the lab learning to use a Fly Cutter. We used it to provide a precision fit on microwave Waveguide (Plumbing Fittings) many people tried several methods and we found cutting the line to with in 1/6 inch to length and make the precision fitted length using the fly cutter gave the best fit and the guys in the field who then installed the final product never had any issue and the final alignment if the microwave system at the broadband frequencies we were using demanded the extra attention to detail to get the required bandwidth. Then we silver soldered the pieces together. Done correctly there were no seams and no solder infiltration of the connector on the inside which is where precision waveguide is required. the small systems were 3 inch by 1 inch the larger was over 6 inch.
All that has now been replaced with fibre optics.
Great Job
Dave C


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## courierdog

Homebrewed:
After reading and re-reading your article, I am more convinced this simple tool can be built to suite the requirements of most  Mini-Mills. Specifically the LMS 3960 or similar units. a single R8 Arbor can be used to hold different sized versions of this cutter.
The unique properties I envision is that of a small "Fleet" of Fly Wheel based cutters using the tool bit of choice in a Fly-Wheel of sorts to provide the diameter of the cut required. One Arbor forms the basis for the tool and different diameter Fly-Wheels using the available tool bit. This reduces the storage issues as only the Fly-Wheels of the differing Diameters are required to be stored.
As you have already stated the sharpening is simple and one Tool Bit can be used in all the differing sizes of the Fly-Wheels.
Many of us have our Work Shops like Harry Potter under the stairs or some other impossibly small location so any and all space is at a premium.
I have even given thoughts to a single large Fly-Wheel with the appropriate holes drilled according the the required radius of the cut required. The holes would have to be spaced about the Fly-Wheel so as not to weaken the structure or upset the balance of the Fly-Wheel. 
Note: The Fly-Wheel now has to be designed as an integral part of the spinning cutter.
Home-brewed, you have spawned a monster that may go viral. ha ha
Again Thanks for Listening


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## homebrewed

courierdog said:


> Homebrewed:
> After reading and re-reading your article, I am more convinced this simple tool can be built to suite the requirements of most  Mini-Mills. Specifically the LMS 3960 or similar units. a single R8 Arbor can be used to hold different sized versions of this cutter.
> The unique properties I envision is that of a small "Fleet" of Fly Wheel based cutters using the tool bit of choice in a Fly-Wheel of sorts to provide the diameter of the cut required. One Arbor forms the basis for the tool and different diameter Fly-Wheels using the available tool bit. This reduces the storage issues as only the Fly-Wheels of the differing Diameters are required to be stored.
> As you have already stated the sharpening is simple and one Tool Bit can be used in all the differing sizes of the Fly-Wheels.
> Many of us have our Work Shops like Harry Potter under the stairs or some other impossibly small location so any and all space is at a premium.
> I have even given thoughts to a single large Fly-Wheel with the appropriate holes drilled according the the required radius of the cut required. The holes would have to be spaced about the Fly-Wheel so as not to weaken the structure or upset the balance of the Fly-Wheel.
> Note: The Fly-Wheel now has to be designed as an integral part of the spinning cutter.
> Home-brewed, you have spawned a monster that may go viral. ha ha
> Again Thanks for Listening


There are worse monsters out there   Anyway, you're the one taking the ball further downfield, so I say Go For It!!

In my mind, the main issue right now is to figure out why the cutter with a larger included angle (smaller grind angle) doesn't work as well.  A larger included angle should produce a more robust cutter.  I suspect the optimal cutter orientation is not exactly tangential to the swept-out circle; or perhaps there is a subtle relationship between the amount of stick-out and the cutter orientation needed to get the best cutting action.


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## courierdog

homebrewed said:


> There are worse monsters out there   Anyway, you're the one taking the ball further downfield, so I say Go For It!!
> 
> In my mind, the main issue right now is to figure out why the cutter with a larger included angle (smaller grind angle) doesn't work as well.  A larger included angle should produce a more robust cutter.  I suspect the optimal cutter orientation is not exactly tangential to the swept-out circle; or perhaps there is a subtle relationship between the amount of stick-out and the cutter orientation needed to get the best cutting action.


Homebrewed:
I am the middle of rebuilding my shop and until it is completed, I am restricted to research, this is when I stumbled across your article.
now I am on the look out for an R8 arbor, that fits the LMS 3960 which uses the 7/16 x 20 threaded arbor. My first thought is to find an arbor on eBay or Amazon. I have found some wonderful ones which come with a Face Mill attached. I am trying to avoid them as I will learn more by using you concept and building the actual cutter. My tooling consists of 1/4 inch Square and Round HSS and Carbloy. I have some simple projects in mind. While I have some end mill which came with the Mill I really like the concept of the single facet Face Mill which can be employed to make the simple Cuts I have in mind.
None of my projects large, as my tooling are Table Top machines this suits my current dreams. Finding the concept of a single facet Face Mill like yours just opens another window of learning which can be done using my existing machines with tooling built in my shop.
My first new tool will have to be an appropriate R8 Arbor to which my plans are to affix various sizes of Face Mill (Fly-Wheel tool holder or the other idea I have running around my head of a single Fly-Wheel with multiple positions into which the tool bit will be slid into and the appropriate screw(s) tightened to hold in place.
Optimized single Tool Holder vs a single tool holder with multiple tool positions.
First the Arbor
Then a first pass at the tool holder
After that multiple versions of different Radius.
Then we try it out as a Single Facet End Mill, ha ha
Any suggestions
T f L


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## homebrewed

A single head with multiple cutter positions sounds interesting.  I've already run into a couple situations where my little tool was just a bit too small.


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## sdelivery

homebrewed said:


> I recently made a small face mill that uses a 3/16" diameter HSS rod for the cutter.  The idea was to replace an indexable face mill with something that would handle interrupted cuts better (I always seem to chip the inserts).  I like the concept of the tangential cutter because they're dead easy to sharpen.  To simplify some of the machining steps I made the face mill in two parts -- the arbor and the holder for the cutter.  I started with a 3/4" rod of HRS for the arbor and some 1.25" diameter 4140 for the holder.  The photos below show a few steps in the process of making it, after I did the initial lathe work to turn the 3/4" rod down to 11/16" to fit my R8 collet and smoothed/faced the holder down to a .486" thick disk (there was no specific thickness target, it just ended up that thick).
> 
> This photo shows the holder in my angle vise.  The vise is set to 12 degrees from horizontal, and I'm milling a flat preliiminary to drilling the 3/16" hole for my HSS rod.
> The slot (machined in a previous step) is .1" deep and .5" wide, and matches a tang milled on the end of my arbor.  With this approach the bolt that joins the two pieces doesn't have to resist the torque produced by the cutter when it's removing metal....and I can make different-sized holders as needed.  To make it easy to accurately rotate the holder 90 degrees, before breaking down the previous setup I also milled two flats on the side of the holder.  That gave me a nice secondary reference plane.
> View attachment 313586
> 
> 
> The photo below shows the holder and arbor assembled to make sure they fit OK.  This photo actually predates the first one shown above.  My old drafting ruler is there to provide a sense of scale.  I was able to machine the slot and tang accurately enough to get a friction fit.  'Course, if I hadn't done so well I wouldn't have mentioned it .
> View attachment 313588
> 
> 
> Below shows the finished product, complete with a shortened hunk of HSS that's been ground to 30 degrees on the end.  I wrote a spreadsheet to calculate the offset necessary to place the tip of the cutter so it is exactly tangential to the circle swept out by the tool, when the cutter is projecting .1" below the bottom face of the holder.  I also used the same spreadsheet to determine where I needed to drill/tap the hole for the set screw.
> After grinding the HSS I did notice a small burr on the end so I honed it with a 600 grit diamond file.  That produced an edge that would easily shave my fingernail.
> View attachment 313589
> 
> 
> Below shows the result when I tried my face mill on a piece of 6061.  I also tried it on some HRS with a .01" depth, full .75" wide cut and it worked just fine.  No chatter, nice smooth surface.  This was done on my Sieg SX2 mini mill, not the most powerful beast around, so I call it a success.
> I was concerned that the cutting forces would push the cutter into the holder but that wasn't a problem.  Not so far, anyway....
> View attachment 313590


Nice job and nice surface finish


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## courierdog

*homebrewed:
I for get where I read where someone actually made a non adjustable cutter, but made provision for more than one tool bit giving the ability to have different radius settings.
With a Fly-Wheel based holder and the simple hole drilled at the desired radius, place different positions around the wheel.
In your example it is a simple hole drilled at 12 degrees. A Fly-Wheel of 3 inches by a nominal 1/2 to 3/4 inch thick will provide sufficient mass. It should be possible to have 4 possible 6 different positions for the desired cutting radius.
Now comes the tricky part. How and where to place the holes. Keeping in mind this Fly-Wheel is a dynamic tool and a simple static balance will be extremely deceptive.. I think it will be an interesting experiment. The results may be insanely brilliant or we may have to consider comment the designer to an institution. ha ha
I found an insanely inexpensive 4 Facet Face / End Mill from China. Delivered is less than $50CDN so I broke down and ordered it.
I have also read that there are several grades of inserts and there are inserts tailored for the cutting of specific material.
Back to our topic of Home Made Tooling.
I like the simple tooling concept as it uses simple everyday cutting material such as HSS or Crobalt which are both easily sharpened on the bench grinder.
I have found that the Tangential style cutter does not seem to suffer like other tooling when it runs into an unknown spot like a weld which can be exceptionally hard. I found while insert tooling will sometimes shatter when it runs into a weld the Tangential tool virtually laughs it off.
I am really hoping your concept will allow me to use the Mill in such a way so I can use my favourite type of current for simple edge removal and such where I normally have to use an end mill to cut away a simple side notch in a surface.
Yours is one of those articles which has my brain running several different ways at the same time thinking of new or at least different ways to construct or use this concept.
Thank You Ever So Much for providing the stimulus for me to get up and finish the shop to move onto more interesting tool concepts.
Your simple and practical approach is what makes this hobby worth while.
Stay Safe, Stay Well
Dave C*


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## courierdog

the next chapter
I am currently working on the computer to design a Flywheel style Fly-Cutter.
I have two objectives
1. to produce flat smooth surface
2. to produce a precise corner for a step
While not totally exclusive the cutter face to achieve either case may require a different approach.
Typically a smooth surface requires a wide radius of the cutting edge while the sharp edge is a corner requires a sharp defined edge tooth cutter.
The simplest approach is a round tool bit for the smooth surface running at a tangential angle to the cutting surface see the concept from https://www.hobby-machinist.com/threads/small-face-mill-using-tangential-cutter.82442/
The Sharp corner I would think would start from square stock tool bit this approach is most easily achieved using any of the conventional Fly-Cutter designs
My current challenge is to design one Disc or Flywheel which can hold either a round or square tool bit.
The basic concept must comply to the above article as it can be accomplished by most people
A square can hold either a Round or Square Tool bit stock.
While a simple 12 degree (facing the direction of the turn) drilled hole can accomplish the concept mentioned above.
The same approach using a square clamp would require the Flywheel to be cut at the desired radius and a 12 degree angled v cut into each side of the flywheel. When mated back together the two pieces would form the clamping square for either a round or square tool bit stock. The design concept is to turn the clamping square such that the tool bit is a tangential cutter capable of providing a square corner in any material it cuts on the edge.
It will also be quite capable of producing a good finish on both the vertical wall and the floor of the cut.
It will take some time mostly in coming up with the working angles as in this design once cut the angle is fixed and the design concept should be capable of using the standard Tangential Tool bit which in a lathe use a 12 degree by 12 degree cutting angle.
The typical grind is a nominal 30 degree. This provides a very strong and long lasting cutting surface and easily resharpened when the cutting edge requires resharpening. The other advantage to this concept is returning to the same cutting depth is a simple matter of adjusting the too protrusion from the Tool holder (Flywheel)
OK this is a very long winded explanation of the concept to bring the tangential Lathe tool approach to the Milling Platform.
The problem with the Mill is rotating the tool and we do not need any additional flying objects seeking more human blood to feed upon. More design work is required to minimize additional protrusions other than the cutting surface.
The thickness of the flywheel is to hide all or most of the tool bit and provide the nominally balanced flywheel
The diameter of the flywheel is to provide the designed radius.

IF there is anyone who can add to this concept you are more than welcome to add your comments as all ideas are welcome, as this is a hobby where we can share our ideas both good and not so good.

I wish I could draw what is in my head for the design concept then it would be much more clear for everyone to see and add their two cents to improve it for everyone else.

Thanks for Listening


----------



## homebrewed

I've been thinking more about the problem I encountered when I tried a cutter with a larger included angle (a shallower grind on the end).  I think it may be related to what the workpiece "sees" as it's being machined.

When you cut or grind a cylinder at an angle, the profile is an ellipse-like form.  A belt grinder would produce a true ellipse because it removes material on a single plane, whereas a grinding wheel removes a shallow arc so the profile isn't **exactly** elliptical, but it's close enough.

It also turns out that the projection of an ellipse onto a plane (i.e., the cutter's presentation to the work) also is an ellipse.  As the ellipse becomes more and more co-planar to the plane of the work, the projection of the ellipse onto that plane flattens out.  In the limit where the ellipse is exactly parallel to the plane, it is a straight line.  This is a horrible profile for a cutter.

It should be noted that the 12 degree tilt angle will also, in effect, flatten out the ellipse.  For instance, the second grind angle I tried was 17 degrees.  In combination with the 12 degrees from vertical, the end result is a very "flat" ellipse, tilted just 5 degrees relative to the work.

This variation in geometry has a bearing on my cutter's performance.  If the DOC is greater than one half the effective "height" of the projected ellipse, the width of the area being cut goes across the entire width of the cutter.  I think you'd see a problem before that because at some point there's not enough "lift", if you will, of the material to break it free of the work (when it then becomes swarf).  So you'd get a nasty raised edge all along the cut path.

Based on the relatively good results obtained with a 30 degree grind angle, there must be a sweet spot for cutter included angle vs. the maximum DOC it handle---and that should also depend on what material you're cutting.  Tough stuff like plastics, which will deform more before they break, will likely be the pickiest, followed by aluminum, various grades of steel and (probably) brass will be least problematic.  Would Young's Modulus be a measure of a particular material's "pickiness"??

Rotating the cutter so it can shear off the raised edge left by a previous pass may be a way to fine-tune the cutting action.  If the raised edge is allowed to rub against the top of the cutter, that's when the cutter will struggle and produce a poor surface finish.

My mill currently is down but hopefully it will back in operation soon so I can test some of these hypotheses.  It won't be possible to vary the vertical angle with my current design but it wouldn't be too difficult to come up with something that could do that.  Basically a variation on a trepanning tool.


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## homebrewed

A quick calculation regarding the ellipse "height"  on my 3/16" HSS rod, when ground at 17 degrees, found that a DOC equal to or greater than about .008 inch would encompass the entire width of the cutter.  I think this pretty much explains why that grind angle produced such a poor result.

The calculation was very straightforward.  If A is the effective angle of the ground facet relative to the work and H is the height of the heel of the facet relative to the tip, H = D*tan(A)/2, where D is the diameter of the rod.  Why the division by two?  Because the halfway point marks the maximum width of the ellipse.

If the vertical angle is reduced to 8 degrees the DOC increases to about .020 inch.  This is not an exact calculation because the effective "width" of the cutter is slightly larger due to the tilt angle.  It's a bit on the optimistic side, but isn't too inaccurate for small deviations from the vertical.

I chose 8 degrees as an example because that is a commonly used angle when grinding lathe cutting tools, there's nothing magic about it.

BTW, my calculations do NOT say that you could actually obtain good results with the 17-degree angled cutter with, say, a .005" DOC -- as I indicated in my previous post, there has to be enough lifting action to break the cut portion loose.  But they would be a starting point.


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## courierdog

Homebrewed: In my case my grinders happen to be 10 inch wheels which produce far less eclipse than the standard bench 6 inch grinder wheel.
Regardless I believe you are onto something. And this is another reason I have invested in the Acute Tool Sharpening Kit. My firm belief is the simpler Diamond style tool bit is easier to use by the average amateur machinist. The key here is keeping the Tool bit simple and thus simpler to sharpen.  In the case of the Tangential or Diamond shaped tool bit a simple single surface can be sharpened by the beginner and achieve amazing results.
My current objective to take your concept to the next level.
My current line of thinking is the make the Flywheel with a split clamp and turned concentric. Instead of the Drilled Hole my initial idea is to mill a two part square instead of the drilled hole. This will permit the use of Round or Square stock as the tool bit.
The two part Square clamp will have to take into consideration the Cutting Angle of a Tangential tool bit that can be of square stock. The Rotational Angle can be adjusted to conform to a Tangential cutter regardless if the Tool Stock is Round or Square.
This allows the Cutter to match the requirements of the finish or cut required.
This is as far as I have gotten so far.
Calculating the angles and cuts required will involve more of a 3D approach which I do not have the program app to design with.


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## homebrewed

I've used OpenSCAD to explore different cutting tool geometries.  I find it handy because you create objects using a script rather than a GUI approach, so it's easy to change angles and then view the result, using its "render" operation.  You can easily move the viewpoint so you can see what the cutter looks like from the workplane perspective.  Here's an example of an attempt to make a simplified tangential toolholder for a lathe:




The standard tangential toolholder must have a slot that is cut on a compound angle, which tilts the bit forward AND sideways.  I thought it might be possible to cut a single angle and then rotate the holder to get something that approximated the sideways tilt.  I think it will work, but it has some disadvantages compared to a standard tangential toolholder -- most notably the possibility of the toolholder body hitting the chuck jaws, or the work hitting the body.  Machining in some extra relief will probably address this, but now we're looking (again) at a more complex machining job.


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## courierdog

Homebrewed: 
Your Visual Tool is fantastic. 
I would like, if you are agreeable to work out the angles. 
In the case of the Flywheel based Fly-Cutter the cutter portion of the Wheel is so that the Tool Bit is in the centre of the cut and the direction of the split is the direction of the optimal cut line. I assume as a starting point, 1/2 inch to the centreline of the split and one allan key on either side of the tool bit to form the clamp. The amount of clamp is controlled by the amount of open split between the two pieces.
Rather than using a single screw to secure the tool bit two screw one leading and another trailing the tool bit.
I am concerned about any potential rotational angle of the tool bit to achieve the optimal Tangential Tool Bit angle.
working out to cut these cutting angles and how to achieve them.
Cutting the angle on the movable piece is a compound angle 
Similar the angle on the fixed portion of the flywheel is also a compound angle 
Both the movable and the fixed portion form the clamping square.
The angle must be such that the Square Tool Bit can be clamped and held at the optimal Tangential cutting angle
The Round Tool Bit can be rotated minimally to suit an optimal cut
Jut the thought of creating a more optimal Fly-Cutter that has a Flywheel to assist in the overall balance of the turning single bit cutter.
Add to this the potential of creating an Tangential cutter within the Flywheel which hoppers both a round and a square tool bit cutter which uses the simple sharpening process of the Tangential Cutter.
While the Fly Cutter is one of the oldest known machining tool cutter it fills a very valuable back stop cutter which can provide the newbie and the seasoned pro with a proven, precision cutting tool.
Thanks for Listening


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## courierdog

Homebrewed:
BTW I have Qty 4 Diamond Tool Holders.
I managed to lift the LMS 3960 off the floor and onto it new workbench.
I use a system of Shackles and Pulleys and a Climbing Rope, to reduce the weight for an old man to manage by himself. ha ha
When I retired for the third and final time in July I got a Tormek Drill Bit sharpening system which allows of sharpening drill bits with a 4 Facet point. 4 Facet drill bits cut through just about any thing and retain their edge longer. Then I obtain the Acute Tool Sharpening Kit from Eccentric Engineering.
These two items alone will keep me busy for a while.
Now I have added the Flywheel Fly Cutter to the list. I will be be busy for some time.
Having time to research and shop time are very prized activities.
Thank you for being part of my inspiration.

And remember you live closer to the ocean than I do so you are more blessed, I was raised with my feet in the North Atlanic and now I am land licked in the Prairies. Poor Me
Stay Safe
Thanks for Listening


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## homebrewed

courierdog said:


> Homebrewed:
> Your Visual Tool is fantastic.
> I would like, if you are agreeable to work out the angles.
> In the case of the Flywheel based Fly-Cutter the cutter portion of the Wheel is so that the Tool Bit is in the centre of the cut and the direction of the split is the direction of the optimal cut line. I assume as a starting point, 1/2 inch to the centreline of the split and one allan key on either side of the tool bit to form the clamp. The amount of clamp is controlled by the amount of open split between the two pieces.
> Rather than using a single screw to secure the tool bit two screw one leading and another trailing the tool bit.
> I am concerned about any potential rotational angle of the tool bit to achieve the optimal Tangential Tool Bit angle.
> working out to cut these cutting angles and how to achieve them.
> Cutting the angle on the movable piece is a compound angle
> Similar the angle on the fixed portion of the flywheel is also a compound angle
> Both the movable and the fixed portion form the clamping square.
> The angle must be such that the Square Tool Bit can be clamped and held at the optimal Tangential cutting angle
> The Round Tool Bit can be rotated minimally to suit an optimal cut
> Jut the thought of creating a more optimal Fly-Cutter that has a Flywheel to assist in the overall balance of the turning single bit cutter.
> Add to this the potential of creating an Tangential cutter within the Flywheel which hoppers both a round and a square tool bit cutter which uses the simple sharpening process of the Tangential Cutter.
> While the Fly Cutter is one of the oldest known machining tool cutter it fills a very valuable back stop cutter which can provide the newbie and the seasoned pro with a proven, precision cutting tool.
> Thanks for Listening



I have attached the OpenSCAD script I used in my simplified tangential toolholder study for your perusal.  OpenSCAD is available for Windows and Linux (but not Macs) and is free.  Of course, my particular script is nowhere near what you want but it does provide sort of a tutorial on how you might proceed.  If nothing else, you could use it in a virtual cut-and-try manner to get the compound angles right.   OpenSCAD has a good online user reference and there are a number of tutorials you can go through.

BTW, I had to rename the file in order to attach it.  If you want to load it into OpenSCAD, change the file extender to "scad".


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## courierdog

So now you know who owns a Mac household.
We have been Apple Exclusive since My Daughter built her first Apple II Clone, which worked BTW.
I bought our first Mac in 1983 and we currently have 5 working Mac in the house and at lease 4 more in states of disrepair.


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## homebrewed

courierdog said:


> So now you know who owns a Mac household.
> We have been Apple Exclusive since My Daughter built her first Apple II Clone, which worked BTW.
> I bought our first Mac in 1983 and we currently have 5 working Mac in the house and at lease 4 more in states of disrepair.


Oops!  Sorry about that.  There might be somebody out there who has come up with a Mac-specific hardware layer for OpenSCAD.  I was going by what the official downloads page has.

Another possibility, although perhaps anathema to a Mac owner, is to use a windows emulator, like WINE is to Linux, and run OpenSCAD with that.


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## courierdog

Homebrewed:
*First* My idea is a 6 inch Diameter cutting radius.
First my Flywheel based Fly Cutter is a nominal 7 inch in diameter
*Second* the Fly wheel is a nominal 1 inch thick.
*Third* the tool holder is 12 degrees round hole drilled  facing the direction of the cut.
*Fourth* a round plug of a nominal 1 in in diameter is a split assembly with a nominal 1/4 inch square hole in the middle of the split assembly
*Fifth* the plug has a gap between halves to allow for proper clamping of the Square or Round 1/4 inch tool stock
*Sixth* the Flywheel  has the nominal 1 inch diameter hole drilled at a nominal 12 degrees facing the direction of cut, the fly wheel has to have a cutter the entire diameter trailing the hole and a nominal 1/2 to 3/4 inch on the leading edge of the hole. The split in the Flywheel will allow a single clamping screw to clamp the round plug with the square hole in the centre.
*Seven* the purpose of the round plug is so the Square tool bit can be rotated to facilitate the optimal cutting angle regardless of round or square tool stock used.

I do not have the ability to draw what is in my head so I hope my words describe it sufficiently for you to grasp the idea. 
While I am unsure how to make some of the milling cuts to form the Square clamp with in the Split Round Plug I am sure with your expertise this would not be a problem.

Such are the wild machinations of a retired old man with time on his hands.

The difficulty as I see it is the milling of the two half squares in the split halves of the round stock turned to fit the 12 degree hole in the Flywheel.

If this concept can be made to work it should be possible for people to build.

What I am learning about the mini0mills is at the low revolutions a Fly Cutter requires is where the brushless motor has the lease amount of torque. The use of the Flywheel will enable the amateur machinist to more effectively use a Fly Cutter to achieve results with a home made tool 

I hope this makes sense to you.


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## brino

Like this?
(although I think you meant fully split into two parts)







I modeled it in Fusion-360. OD=1 inch, 1/4" square hole and 2.5 inches long.

My thoughts:
-the OD could be 1/2-inch instead of one inch as modeled here; less material to try to spring
-the cut could continue into the other side to allow more "spring" (but still not thru cut)
-the square hole could be made with a broach (see clickspring video below)
-the clamp screw used to close the gap to grip the square cutter must not fall on the cut; therefore some angles of the square cutter are not allowed


ClickSpring making a square broach:





-brino


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## courierdog

Brino:
Yes my idea was a total two part as broaching is way beyond my abilities and also above the desired target audience as well.
Another note is the Flywheel itself also has to be cut such that a single screw on the trailing edge of the flywheel will provide sufficient clamping on the two piece round clamp (held in the round hole drilled into the Flywheel )to hold the tool bit (round or square) without risk of slippage.
Also I would like to reduce the round portion to the minimum required to create the clamp and find inside the round hole in a manner that the single screw on the trailing edge of the Flywheel will provide sufficient clamping on the tool bit held within the Round tool holder which is held within the 12 angled hole in the Flywheel.
I am trying to think of a simple means to rotate the round tool holder so when square tool bit tangential sharpened can be rotated easily to enable the optimal cutting angle. This is useful when cutting for optimal material removal or for optimal surface finish.
Is this a better explanation of my concept.
The bigger question is how achievable is the round clamp to hold a square or round stock ie 1/4 inch HSS or cobalt tool steel (round or square)
I hope I have clarified what I am thinking.
I wish I had the drawing tools and the ability to use the app to draw what is in my head.


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## courierdog

I also for got to mention your drawing illustrations which are just great. and do describe in pictures your version of my thoughts.
Now you have to cut the pieces totally in half.
I will mention that Gary of Eccentric Engineering says that a V on each side creates a stronger clamp than using a Square trough on each side. This is how the Diamond tool holder is designed to clamp onto the tool bit in either round or square stock.
My problem is how to cut the "V" in round stock.
The other approach is to make the "V" cut in the middle of square stock cut the long piece in half place the "V" one on top of each other (The resulting square has to be slightly less than 1/4 or what ever size the tool bit stock will be so there is sufficient room to clamp.
then weld or drill and tap a hole in either end to hold the two pieces together so the single piece so it can be put into a lathe and turned to the desired size for the hole in the Flywheel and will become the interior clamp to the external Flywheel clamp.
Let me know if this makes sense or not.
Thanks very much for listening to an old man.
Dave C


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## courierdog

Brino:
Please note this concept is what Homebrewed came up with at the beginning of this thread.
I am just expanding upon his idea. To take it from a simple small Face Mill into a larger Flywheel base Fly Cutter suitable for the low torque Mini Mill. At the speeds for a Fly Cutter to operate and provide an optimal finish the Fly Wheel inertial forces should minimize the actual low torque or the motor. The simplicity of the Fly Cutter with the added cutting ability of the Tangential cutter and simplicity of the single facet grind to the tool bit should provide for an enjoyable build and hours of pleasure watching the magic of a simple home made tool provide a masterful cut and finish.


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## homebrewed

"I will mention that Gary of Eccentric Engineering says that a V on each side creates a stronger clamp than using a Square trough on each side. This is how the Diamond tool holder is designed to clamp onto the tool bit in either round or square stock."

In that case two 90 degree Vees make a square rotated 90 degrees, but it's capable of accommodating round and square bits.  That's not a bad suggestion....but....as Brino mentioned, you don't want the split to line up with the fixing screw (or fixing force).  So in this case the screw must be on the radius and act as a set screw, not part of a slit/clamp scheme.

As far as making the round holder with the internal Vee.  There are 90 degree end mills.  Or a standard flat end mill could do it if the work is tilted 45 degrees relative to the EM but the challenge is getting the dimensions right -- the depth of the groove affects centering as well as the width of the vee.

I'm wondering if you could mill a vee in two pieces of square stock, fix them together and then turn them into a cylinder.  There would be a lot of steps that could go wrong there, but no more than what you'd encounter if you start with round stock and try to go the other way.


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## courierdog

The case of using the Round milled with the split square centre the clamp action is provided by the split on the Flywheel clamping down on the split cylinder held in the angled hole of the Flywheel. OR this is is my envisioned concept as of this minute.
All of this presents some challenges in the milling and Turning.
If you have or have seen the Diamond Tool holder you will note in the relaxed state the clamping jaws do not quite meet and in the clamped state there is quite a separation between the two parts of the clamp. So I do not believe the concentric behaviour of the clamp will be a huge concern and the actual clamp is the Flywheel clamp acting upon the split clamp of the round plug with the squared hole in the middle. I hope I am describing my idea correctly.
The Round inner clamp is being squeezed by the Larger, Split in the Flywheel squeezing down upon the round clamp.
They is where I wish I had the tools and the ability to draw the concept as an image. then I would be, much more clear as to the approach I am attempting to apply


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## courierdog

1.  I have drawn a Circle to represent the Flywheel
2.  next I drew a second smaller circle to represent the drilled hole
3.  I attempted to draw a square within the smaller circle
4.  I attempted to draw a line through the square which bisects both the inner circle and the square.
5.  I drew another line on the flywheel cutting through the flywheel beginning on the leading edge of the smaller circle and continue to the edge of the flywheel
6.  I drew a line to represent a single screw on the trail edge of the inner circle which is to act as the single clamping screw clamping the flywheel onto the inner circle clamp which holds the square or round tool stock in the split circle clamp.
Does this poor drawing help anyone to better understand what I am proposing.
Comments please


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## courierdog

I could hand draw this picture and add Labels to the portions to better define my idea.
I know how to draft but it has been over 40 years since I last did any serious work.


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## homebrewed

@courierdog, using OpenSCAD I created a very pared-down version of what you're proposing.  Some renderings are shown below.

There are some obvious things that need to be addressed.  First, the diameter of your round tool holder is too large, or the diameter of the flywheel needs to be increased.

Second, the toolholder needs to be pulled up a bit so its heel doesn't rub against the work.  This is less than ideal because it means more of the cutter is unsupported.  Milling the bottom of the holder so it is flat relative to the body would improve this; but see the next paragraph.

Third, it's my understanding that for best performance the cutter needs to intersect the work so its cutting action is parallel to the swept-out circle being machined.  This won't happen unless the holder is offset, because the cutter is coming out at a 12 degree angle.  You need to define how much cutter stick-out you want.  Yes, you could rotate the holder but it could be difficult to rotate it just the right amount; and if you mill the bottom of the holder to flatten it, you want to KNOW what the correct rotation angle is.  Better to set things up so it's easy to install the cutter correctly.

These renderings were done with a body diameter of 7 inches, a toolholder diameter of 1 inch and offset to machine a 6 inch diameter circle.  It was tilted 12 degrees.  I also added the 30 degree grind angle on the end of the cutter.

This study required 39 lines of OpenSCAD code (including comments).


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## courierdog

*homebrewed:
You got the basic concept*
Yes the interior round (Plug) clamp only has to be big enough to hold the Square or Round (nominal 1/4 tool stock)
Yes the bottom portion will have to be milled such that it is mostly flush with the base.
If we back up and look at the Diamond Tool Holder and how the tool T*urns* or F*aces* metal on the lathe.
The two extremes on the cutting angles, worst case 10 degree rotation.
Once the actual optimal cutting angles are defined for the type of cut or finish is defined very little of any rotation will be required.
I have found when using the lather I have one QCTP insert set up on the Right hand tool and the other holder set up on the Left hand tool
The amount of projection of the actual Tool is held to only what is required.
This is straight forward when dealing with the flat surface finish
Let us now consider using the same cutter to create a step cut along a side of a bar
Example we want to cut a square bar.
The design calls for a 1/8 inch deep by 1/8 inch wide.
Doing this with a Fly cutter is more time consuming but we are talking a simple home work shop where the cost of purchasing a tool may be out of the question.
We have this newly created Flywheel based fly cutter so now we are looking at cutting (slowly) a step into the side of a piece of metal. 
So in this instance the cutter will have to be strong enough (reason for the 1/4 inch tool stock or even 5/16 tool stock) so the tool bit can safely extend beyond the base of the Flywheel Tool holder.
Now go back to my poor drawing,
The Flywheel needs to form the clamp of the tool held inside the split cylinder.
I think we are now on the same page.
Back to you for your comments


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## courierdog

@homebrewed:
Please keep in mind, the objective is a simple amateur machinist project for construction using a mini lathe and mini mill.
The spindle is a nominal R8 which is used on the majority of Mini Mills. The current Mini Mill uses a 500 watt brushless motor.
These motors work well using higher RPM and thus the use of the Large and Heavy Flywheel which has  the spinning mass to mitigate the interrupted cut of the Fly Cutter.
The vast majority of Fly Cutters have little mass and a very unbalanced and potentially more dangerous rotating cutter which cannot be seen and leaves the all too real risk of something being snagged by the spinning mass. I have seen this happen and it a very messy sight when a person looses his/her mechanical safety concentration.
My ideal spinning mass should be totally without projections which can snag any wayward appendage or loose material.
The cutting side of the tool is the only place where cutting action should happen.
The design goal is for the visible, upper and the  periphery surfaces should be virtually idiot proof.
I hope this makes sense and allows you to better see my minds view.


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## homebrewed

courierdog said:


> @homebrewed:
> Please keep in mind, the objective is a simple amateur machinist project for construction using a mini lathe and mini mill.
> The spindle is a nominal R8 which is used on the majority of Mini Mills. The current Mini Mill uses a 500 watt brushless motor.
> These motors work well using higher RPM and thus the use of the Large and Heavy Flywheel which has  the spinning mass to mitigate the interrupted cut of the Fly Cutter.
> The vast majority of Fly Cutters have little mass and a very unbalanced and potentially more dangerous rotating cutter which cannot be seen and leaves the all too real risk of something being snagged by the spinning mass. I have seen this happen and it a very messy sight when a person looses his/her mechanical safety concentration.
> My ideal spinning mass should be totally without projections which can snag any wayward appendage or loose material.
> The cutting side of the tool is the only place where cutting action should happen.
> The design goal is for the visible, upper and the  periphery surfaces should be virtually idiot proof.
> I hope this makes sense and allows you to better see my minds view.


My mill is a MicroMark benchtop mill with a 500W brushless motor as well.  R8 spindle.  So I'm dealing with similar machine limitations.

Milling a step with this proposed tool will be limited by the stickout of the cutter.  Clearly there is a limit to how far out it can project before you run into problems, so there will be a limit to how high the step can be.  The rectangular cutter definitely is the one you want for this, a round cutter will produce a rounded corner on the bottom.


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## courierdog

@homebrewed:
Just to clarify, My Mill and Lathe are from the Little Machine Shop. The Mill is the 3960 and the Lathe is the 3536 8.5 x 16
My thoughts on the initial maximum DOC is a nominal 1/4 inch absolute maximum is 1/2 inch but this has to be worked on to design this for the Amateur Machinist who may will push things beyond the specified maximum.
Designing a tool which can be built simply which can be employed to make and do things without the need to buy expensive insert based tools and more importantly sharpened by the Amateur Machinist.
A single facet tangential cutter is able to cut much more that the average multi-facet tool which requires more time and practice to accomplish and does not last as long when actually cutting metal.


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## homebrewed

FYI, the spreadsheet I attached to message #3 in this thread calculates the offset needed to get the geometry right for a specified amount of cutter stick-out.  More or less stick-out will result in a less-than-perfect cutting situation, but I'm not sure how that will affect actual use.  I'd expect tools with a larger machining radius to be less sensitive to this variation.


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## courierdog

Homebrewed & brino
I have been struggling with the angles, and then I went and took the Diamond Tool Holder off the Lathe and began to play with it so I could more appreciate the Tool bit and the required cutting angles.
Here is another person who has been working with a similar concept.
I found someone who has had a similar idea.
Tangential Flycutter - https://www.hobby-machinist.com/threads/tangential-flycutter.32367/
To obtain the most from the Tangential Cutting tool the cutting force must be against the entire tool and not any of the edges.
This changes the entire view of how the tool interacts with the tool holder, in my idea, the flywheel.
The 12 degree tool angle, at the beginning of this thread is not how I now think I want to pursue.
The 12 degree tool angle is up from the work surface face similar to angle approach in the attached Tangential Flycutter thread.
This changes hot the tool bit clamping method.


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## brino

@courierdog,

Thanks to the link to that thread by @Jim2.
I don't know how I missed it.
I just read the whole thing, what a great build!

The other good news is that he is still active on this forum; so perhaps he would field any of your questions.

-brino


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## homebrewed

courierdog said:


> Homebrewed & brino
> I have been struggling with the angles, and then I went and took the Diamond Tool Holder off the Lathe and began to play with it so I could more appreciate the Tool bit and the required cutting angles.
> Here is another person who has been working with a similar concept.
> I found someone who has had a similar idea.
> Tangential Flycutter - https://www.hobby-machinist.com/threads/tangential-flycutter.32367/
> To obtain the most from the Tangential Cutting tool the cutting force must be against the entire tool and not any of the edges.
> This changes the entire view of how the tool interacts with the tool holder, in my idea, the flywheel.
> The 12 degree tool angle, at the beginning of this thread is not how I now think I want to pursue.
> The 12 degree tool angle is up from the work surface face similar to angle approach in the attached Tangential Flycutter thread.
> This changes hot the tool bit clamping method.


That design stays closer to the geometry associated with a standard tangential (or diamond) cutter.  It's a bit puzzling why he didn't get an excellent finish, particularly since his DOC was only .003".  It doesn't look like chatter so perhaps his feed rate was a bit too high, but that's a pure guess on my part.  I'd ask @Jim F about that, and for follow-on observations on its performance. 

Due to the shallow angle you will get a much larger variation in the cutter-to-work geometry if you extend the cutter to get a larger DOC.  Tradeoffs....always tradeoffs


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## courierdog

The comments really help me to better understand the Tangential cutting concept better and refocus the effort. The Diamond Tool holder (a Tangential Lathe Cutting Tool Holder) is my starting point for the cutting, sharpening and tool holding process. The originator of the design Des Burke himself went back to basics several times before achieving the current working design. I was directed to this tooling by a video by Rudy Kouhoupt. What has really stuck with me about using this type of tooling is the ease of the initial shaping and routine sharpening of the tool bit material. Turning metal on the lathe using this tool has been reduced to simple steps  and I derive a great deal of satisfaction using a simple tool to achieve my desired results.
So after my long winded explanation back to basics, after reading your original article which was well put together and pushed me into actively wanting to have an Mill Equivalent Tool for simple surfacing and edge cutting. The Lathe Tangential Tool has all the forces pushing on the tool bit through its length. The Clamp therefore is only holding the tool against a vertical force pushing down upon the vertical tool Bit (Post) this can be seen in the engineering field of Power Tower design where the individual tower is holding up or supporting the weight of the power line which is horizontal but the weight is directed down vertically on the tower.
The Tangential tool similarly is supported in such a manner as to disperse if you  will the force of the work removing the metal pushing directly through the length of the tool bit. This means the tool bit has to be orientated so that the single facet ground onto its leading edge is being supported by it entire length not by any of its sides.
This allows the Tool bit to protrude beyond the clamp (with in reason) without the same risk of collapse as a bit which has unsupported side thrust placed upon the bit. The entire Tool bit length must be positioned behind the ground facet.
I hope this better explains without getting into the mathematics of the thrust forces involved.
Please be patient with and old man and his rambling thoughts


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## courierdog

Homebrewed and Brino:
I really appreciate your comments as it helps me to better understand the mechanical concepts. While I did have to study some mechanical engineering my focus was on Electrical and even then more on the RF broadcasting and later Antennas in particular. The entire amateur machining is new and very exciting to learn new (old to most here) things to me. Learning is a life process and you both are very helpful to an old man groping his way along.


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## homebrewed

Always willing to help when I can!  And I am always are ready to say:  "I don't know", rather than to make wild-ass guesses.

I'm learning too, and this is a great place to do that.  One thing I've been impressed by is the sheer range of knowledge you can find here. And so freely given.  Astonishing.  There are those who hoard their knowledge as something to be doled out to the privileged few.  My lifelong philosophy has been:  there are no secrets that divide us.  Only differences in the individual's ability.

Mark


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## courierdog

Mark:
A man after my own heart. What I have seen so far is the experienced people take time to assist people coming into the hobby so they are able to develop their skills and use their mini machines to achieve more than what was originally envisioned by the Machine builders. Forums like the Hobby Machinist are a pleasure to read and join as I have not seen any form of actual or implied intimidation. 
I have been attempting to work through the design and figurative build of a Fly Cutter as an inexpensive and achievable tool build using HSS tool steel as the cutter. My prime interest is devising a tool using the simple Tangential Tool. My reason again is simplicity of the shaping and sharpening of the tool bit. There is more design involved in the tool holder however this is offset by the simplicity of actual day to day use in the hobby shop.
The secondary article I also found on the Hobby Machinist forum illustrates the Tangential Tool holder I am used to in the Diamond Tool Holder. Jim in his Tangential Fly Cutter places the Tool cutter in the same manner as the Diamond Tool Holder.
I received the call to go to bed so I will sign off for now and come back in the morning to continue my thought.
Again thank you for your patience and helpful comments


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## Larry$

Rambling thoughts on how to make a 90 degree V slot in 1/2 of a 1" diameter  rod. 
Required:  square collet block & collet
Make the parts *longer* than needed and bring to length as a final operation. 
With enough rod sticking out of the collet block, mount in the mill vice. 
Touch off on the top of the rod. Machine away 1/2 of the rod diameter.
Rotate the block 90 degrees and mill the V. Saw the first piece off.
Repeat the process for the 2nd piece but do not cut it free from the rest of the rod.  
The loose piece can now be stacked on the still connected piece and put back in the collet. Leave the bottom part sticking out from the other part enough to be able to indicate it square to the mill. The extra length of rod sticking out the back of the collet will allow you to twist the slightly snugged parts square to the mill. You can now drill, tap & counterbore for one of the screws that hold the two halves together. Put that screw in.
The screw(s?) to clamp the tool bit in place can now be drilled and tapped to hit the corner of the tool bit. 
Cut the parts free and rotate to put the other clamping screws in. You can use the tool clamping hole as a reference back to square. 
Finish the ends.  Optional? Using the hex collet block put wrench flats on the top of the sleeve that sticks above the main disc body to allow the tip of the tool to be rotated for best finish. (I'm assuming this sleeve is being clamped into the main body so it can be adjusted.) 

The sleeve for the round tool bit can just be drilled, reamed, drilled for clamping screws & slit. 
Having some sort of indexing marks on the sleeves relative to the body would make life easier. 
Any possibility that this would work?


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## courierdog

LarryS
Excellent approach, I have had more time to digest the various comments and suggestions. the interior Round Clamp should have the minimal material to for the clamp on a piece of HSS Tool Stock, worst case is the 1/2 in stock and the interior square clamp is cut depending on the end users cutting tool requirement. We have to keep in mind the interior clamp need only be large enough to hold the tool stock as the clamp which really the large Flywheel and can comprise of one or two screws squeezing down upon the inner circular clamp.
The Tangential tool alignment I have been reminded is 12 degrees tilt up from the Horizontal not as I had first thought of as 12 degree down tilt from the centre line of the vertical mill Spindle.
So this puts most of the actual tool inside the Flywheel where it cannot be seen from the exterior.
My approach is to drill this 12 degree through the exterior of the flywheel.
This approach is for two reasons.
1. the Tangential tool angle
2. hide the entire cutter and interior clamp within the flywheel.
3. the flywheel will be cut along the drilled hole for the cutter clamp
Keep in mind this is all in the wetwear of the mind at the moment and as anything in there is subject to erasure at the slightest disturbance in the blood flow. ha ha I have to blame the unreliable memory and poor thought process on something. ha ha
Once I begin cutting in metal many of the great ideas vanish at first contact.
The idea of the nominal 6 inch cutter came originally from the LMS Specifications of 2 inch maximum, having come from the old school of single cylinder motorcycles where the flywheel was as physically large as possible and twice as heavy as required.
When you geared down these beasts you were virtually dragged to a halt. The reverse is also true any instantaneous speed change was resisted with equal force. This is why the old steam powered engines had massive flywheels. The purpose was to have a constant speed. Take this idea and think now of the Brushless motor. which is great at high RPM but has very low torque at Low RPM. Hence use a large massive flywheel which is keep at speed by a powerful but low torque motor. So once the Flywheel is running at speed any attempt to slow it down, the interrupted cut of the flycutter will be resisted by the inertia of the flywheel, and those that worry about the spindle bearings and the interrupted cut pounding on the bearing, this effect as well is minimized by the inertia of the flywheel. While this approach is contrary to todays high speed and carbide insert mentality the physics is sound and if one has the applied math to calculate out all the forces at work you will find good old flywheel mass wins out over momentary attempts to slow it down. For other example of the Flywheel approach is to analyze the industrial age factory where one small steam powered engine supplied power to one central massive flywheel which intern drove many shafts with additional flywheels and take offs to provide an entire factory with a centralized spinning source of power and each take off required different speed and amounts of power which was constantly changing yet the main powered Flywheel was held constant by one single small motor.
This is jut my attempt to turn back the clock so to speak to achieve with our tiny Mini-Mills a smooth cutting cutter capable of producing with minimal tooling and cost what the higher speed and expensive insert tooling can do.
Yes this approach can be taken to far but remember this is a hobby and not a commercial venture.
Plus any who think time is not valuable to a retired person had better realize we have far less time to spend than younger people so yes ever second does count. some spend their resources as money we spend a finite unit of time.
Thanks for Listening to an old man


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## courierdog

Some progress, on the proposed Flywheel Fly Cutter, thanks to input from several people.

1.    Mass and Diameter nominal 6 inch cutting radius
2.    Tool Holder, Square Collet style tool holder, the Collet allows the tool to be rotated within the Flywheel for the optimal cutting angle. the collet approach is what I was thinking all along but did not have the terminology to define. Now the idea have been suggested that the tool may be pushed back by the forces of the Interrupted cut. Hence the concept of the collet to hold the Tool bit.
a straight shank is simpler but a slight taper would possibly provide a more secure clamp and resist tool push back.
3.    Flywheel drilled such that the Nominal Tangential Cutting angles are a result of the angle and direction of the hole drilled in the Flywheel. the collet is proposed to be clamped into the mass of the Flywheel. Please note the 12 x 12 angle is up from the horizontal not down from the vertical. I hope that makes sense. al describes this in his approach Tangential Fly-Cutter https://www.cgtk.co.uk/metalwork/sx3mill/tangentialflycutter
4.    Spindle attachment to Flywheel, proposal is an R8 FMB22 Arbor, this allows the arbor to be removed from the Flywheel for storage between uses.
Now can some other voice be heard on this and I know we have people who can apply a CAD drawing to this modified concept.
It is really great working with so many wonderful people who have brought so many ideas to this concept. I certainly do not take credit for the design. my only contribution is a feeble attempt to bring the idea together where it can be built by even the novices on the forum. This last part is where the vast wisdom of the collected forum can be utilized to bring the design and machining techniques to focus on a project which enable the novices to build a usable tool with simple, tooling and the written guidance of senior members.
Stay Safe, Stay Sharp, find a fresh sheet of paper and put your thoughts on paper then, fingers to the keys for input to this collective project.
*Happy New Year*


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## homebrewed

Since the cutter in your latest approach is inclined just 12 degrees from horizontal, that will substantially affect your collet design.  It may need a conical nose in order to keep it from hitting the work before the cutter does.

If you haven't done it already, I'd suggest getting out your mechanical drawing stuff and start drawing in order to see what constraints you're dealing with.  Scaling the dimensions up will make it easier to draw, and won't alter the geometry.


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## courierdog

homebrewed:​My collet for lack of a better term is a round external shape with a square inner shape. 
IT has been been suggested I also require a physical adjustment to prevent push back of the tool bit into the Fly Cutter Housing this will complicate the current approach. 
As a Starting point this would mean a blind hole with the opening at the point where the tool bit is facing the work piece. The Rear or the blind hole bottom will facing away from the Work Piece. If required it will be threaded to allow for  a threaded screw and lock nut to secure  the working position of the tool cutter. The hole drilled for the collet will be be clamped using a split cut through the flywheel bisecting lengthwise the collet hole. The actual clamp at this point will be a single screw located toward the tool bit exit and above the tool bit.
Any suggestions at this point.


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## homebrewed

courierdog said:


> homebrewed:​My collet for lack of a better term is a round external shape with a square inner shape.
> IT has been been suggested I also require a physical adjustment to prevent push back of the tool bit into the Fly Cutter Housing this will complicate the current approach.
> As a Starting point this would mean a blind hole with the opening at the point where the tool bit is facing the work piece. The Rear or the blind hole bottom will facing away from the Work Piece. If required it will be threaded to allow for  a threaded screw and lock nut to secure  the working position of the tool cutter. The hole drilled for the collet will be be clamped using a split cut through the flywheel bisecting lengthwise the collet hole. The actual clamp at this point will be a single screw located toward the tool bit exit and above the tool bit.
> Any suggestions at this point.


The DIY tangential toolholders for lathes that I have seen don't have a screw underneath the cutter to prevent push back.  Maybe it's a solution looking for a problem?


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## courierdog

I was thinking more along the line of the clamping screws on the periphery and the potential stop and adjust met screw would also be from the periphery.
With everything that the current concept the thickness of the Flywheel is increasing.
1. the original cutting diameter is a nominal 6 inches or a nominal 6.6 inch diameter plate
2. the original thickness of the of the Flywheel Plate was 1 inch mow this has grown to a nominal 1.5 inches
3. I am still looking at the collet style toolholder with the hole drilled into the Flywheel at the nominal Tangential 12 x 12 degrees so the actual tool bit can be sharpened as a typical Tangential Lathe tool bit.
The only reason for the circular Collet style tool holder at this point is to allow for some degree of rotation of the tool bit to achieve the optimal cutting angle. With the Tangential Tool it is extremely important to optimize the tool face to the work piece for optimal cutting and finish plus the ideal is to transfer as much heat into the removed chip and away from the tool and the work piece. This is a delicate balance of the angle of approach and the tool grind applied to the cutting bit.
The idea of the collet is to optimize a clamp for a square tool bit that can be rotated to achieve an optimal cutting angle.
I was thinking of four pieces surround the tool bit and turn in the lathe to size to the point of minimal external collet while providing a means to hold in a split clamp with in the Flywheel.
More thought is required on how to accomplish all of this using the KISS principle.
Thanks for Listening


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## Tipton1965

DavidR8 said:


> Flycutters freak me out a bit as they whirl around looking unbalanced and ready to fly apart.
> 
> 
> 
> 
> Sent from my iPhone using Tapatalk


When I first started working in a machine shop I knew nothing about the trade.  A co-worker had a milling machine all set up for me to do some fly cutting.  All tooling was made in house and the fly cutter used a couple Allen head bolts to hold the cutting bit in place.  This co-worker said "Make sure that bit is tight.......I'd hate to see you wearing it in your chest."  As it turned out fly cutters were one of my favorite things to use.


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## courierdog

I can agree with you watching a Flycutter in action is like watching a plotter draw a circuit board. Watching a Face Mill or an End Mill does not have the same appeal of a Fly Cutter up against a huge piece of uneven metal.
This is especially true where the Fly cutter has a large diameter and the work piece starts as a very uneven rusty hunk of cast iron.
The speed is slow and the cuts are extremely fine to prevent mishap with no lubricating fluid used. while hard on the work piece, the cutter bit and depending on the care used on the machine and tool setup can tarsier a lot of the shock of the interrupted cut to the Spindle.
Using a Large Flywheel and care is given ensure as much balance as possible is given to the cutter set up, the mass of the flywheel resists the sudden slow down effect of the interrupted cut. This is where the Tangential cutter comes in. The concept of the Tangential Cutter be it on the Lathe or the Mill is such that the cutting angle is much more efficient and transfers more of the heat to the removed chip, less to the cutting tip and thus the Cutting bit and the work piece remains cool.
There are those who live the Tangential cutter and those that hate the Tangential cutter.
If you look at the current high end milling tools you will notice there is a move to Tangential Insert cutter for the Mill claiming tremendous increase in the speed and efficiency of the removed metal.
I find this move by the commercial concerns very encouraging as it does point the way forward.
While those of us in our tiny home shops are not going to rush out an purchase an expensive cutting tool we can move forward in small ways in adapting the concepts in a small single facet cutters such as the Fly Cutter to achieve in a small and slower means the principals employed by the big machine shops and do it on a very lean budget.


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## courierdog

Home-brewed
I received an email from Gary Sneesby of Eccentric engineering, he sent along a photo of his version of a fly cutter.
This uses the Diamond Tool Holder as the tool bit holder.
In my case this will require a nominal 4.5 inch diameter concentric disk made to attach to an R8 Arbor such as an FMB22.
On the one side it will require milling to allow for fitting of the R8 Arbor
on the visible (as Shown) a nominal 1/2 slot x 1/2 inch deep with a notch cut to allow the Diamond Tool Holder to have some of the clamp mass inside the circular disk mass.
On the edge would be three to 4 clamping screws
Under the shank of the Diamond Tool Holder would be an R8 Arbor holding screw.
While it may look a little awkward I think as I work through the various dimensions, drillings and milling cuts it should be a workable solution.
IF anyone has a suggestion I would appreciate it.
I like using the Diamond Tool Holder, and if I am able to make a means to secure it to the mill in a safe manner and allowing the tool to be used as a Flycutter.


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## savarin

I've also used the diamond tool holder as a fly cutter.








						80mm long focal length refractor
					

Still waiting for the block of ally so I started on the finder scope. I'm using a doublet from an knackered binocular.   The right hand joiner was already made, one end of the tube was threaded, so today  I cut it to length and threaded it, also there is approx 30mm of taper on the inside with a...




					www.hobby-machinist.com
				



page 6 and 7
I can see a purpose built holder is way better.


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## courierdog

Savarin, it is good to know, others have tried using the DTH as a Flycutter.
Note: After reading your apology at the bottom, your first statement made a lot of sense.
I was afraid people would think I was a little of the level for even suggesting it.
My rational is to try Garry's suggest as a proof of concept, of the Tangental Cutting process configured as a FlyCutter.
After the Proof of concept is built and providing it does work as intended, 
Decisions can only be made after proving Garry's concept.
I am working through the design in my head, trying to think through how to draw it, so it makes sense.
There are three levels
Top - Arbor Fitting
Middle Attachment Plate
Bottom Diamond Tool Holder Clamp.
Have I missed any thing.


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## savarin

The only thing I found on my version was the cutting angle wasnt quite orientated the best which is why I went with the round tool bit for some adjustment.


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## courierdog

While a purpose built tool is always, better, as it should factor in more of the cutting details.
I want to start with Gary's concept, to get a better handle on the fly cutting concept while using a tangential cutting face.
While the diameter of the resulting tool is technically outside the operating parameters of the Seig X2 Mill it should be capable from a proof of concept stand point.
Creating a stand alone tool involves an entirely different approach. While adapting Garry's concept while quire physically large should be manageable. IF, I can work out at the dimensions and cutting solutions.
It would be nice if I had a local machinist friend to sit down and discuss how to approach the project.


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## courierdog

savarin:​Until I looked up Townsville on the Map, I had no idea you lived way up in Queensland, that is 28 hr 16 minutes or 2635 Km to Melbourne which is comparable to Edmonton to Toronto 34 Hr 2 Min or 3335 Km
We both live in rather large countries.
My daughter moved to London UK as she can travel (prior to Brexit and COVID) to Europe easier and cheaper than from Canada.
I have driven from coast to coast, Halifax to Vancouver and gone over to the Island to Victoria via the ferry.
As a drive that is 58 hours 12 minutes or 5781 Km Not a drive for the winter time as the snow can be terrible and the ice is treacherous.
Here the high of the Simmer is +35C while the low of the winter is a nominal -40C
My sister moved back to Nova Scotia when she retired. Summer +19C Winter -9C


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## courierdog

It has been a few days now. I was hoping for more comments and other input. Homebrewed came up with a simple solution. However, I would like the tool bit to laid down so to speak. 12 degrees from the Horizontal rather than 12 degrees from the Vertical.
1. Have the tool bit rotated 12 degrees outwards from the tangent point and at right angles from the centre.
2. Have the tool bit tilt downwards from the horizontal by 12 degrees.
I have been attempting to draw this on paper and am having some difficulty. While I know what I want in my head, putting it down on paper is not easy. I also attempted to use the various drawing applications I have any I am unable to get my head around the applications to make anything useful.
If only I could sit with or explain to someone who has the time, patience and ability to take an idea and bring it to life, so to speak on paper (Computer screen)
Well it is a thought, which requires a person with a different talent which I do not possess.
Thanks for Listening



​


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## homebrewed

Maybe part of the reason for the absence of responses is that you're looking at some tricky-to-calculate compound angles.  The first one is setting up to drill the hole for the toolbit/holder, and the second is setting up to drill/tap a hole for the set screw.

I did some fooling around with OpenSCAD and got something that may have the geometry you want, but it was done completely by using trial-and-error.  And it doesn't hand you any way(s) to set up them-there compound angles. 

Anyway, here are a couple of views of what I came up with, starting with a view from the bottom showing the 12-degree rotation angle around Z (which is into the screen).




And from the side:


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## brino

Thanks @homebrewed that really helps me!

I was unclear on what @courierdog was describing.
I wanted to help, but felt lost....not understanding what he was picturing.

-brino


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## homebrewed

brino said:


> Thanks @homebrewed that really helps me!
> 
> I was unclear on what @courierdog was describing.
> I wanted to help, but felt lost....not understanding what he was picturing.
> 
> -brino


I THINK that's what he is after .  It's not all that clear to me why he wants the cutter rotated 12 degrees away from the tangent.  Maybe to better control the chip flow?


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## courierdog

homebrewed,​I think you have captured what I was thinking except I was thinking the tool bit should point outwards as opposed to how you have it pointing inwards.
Having the drawing in front of me, illustrated as you have done, I really appreciate this. It does however really point out how much more difficult this method would be to build, especially if I want a square tool bit as opposed to the round tool bit you have chosen. This is why I I am looking at this with non Machinist eyes or abilities.
I come from an electronics background.
My reasoning for wanting to stay with the square tool bit is it would be interchangeable with my existing tool bits.
The really encouraging thing is how you have captured the essence of my concept with your drawing.
This is truly amazing that you have this ability and seem to be able to bring to life a concept described to you.


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## courierdog

@homebrewed,​What really got me was having this drawing in front of me, made the possible machining  so straight forward.
In my head I am trying to imagine this using a flywheel (Disc) as the basic tool holder.
I have some tooling which uses the R8 Arbor and especially the FMB22 tool as it has both the R8 plus the two pins for added turning stability. It works really well for the face mills I acquired.
I have a real soft spot for FyCutters due to their simplicity.
Again Thanks ever so much for taking the time to draw the illustration.


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## courierdog

As to the reason, for the 12 degree outwards is to match the idea put forward by Gary from Eccentric Engineering.


You will notice the tool bit points outwards by 12 degrees.
After seeing your drawing I also realize this will be the road less traveled as well.
I hope this make it a little more clear as to my reasoning.
As another person already pointed out having any large unbalanced object flying about on a mill just makes me nervous.
This is what drew me to your approach in the first place.
Your simple approach is by its nature more balanced than the vast majority  of the FlyCutter I have seen. Any Single Facet Cutter will by its nature be unbalanced.Thanks for your patience and your generosity in time and effort making the conceptual drawing.


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## courierdog

I forgot, As the Outward angled Tool bit protrudes beyond the radius of the flywheel, enabling the cutter to cut unhindered beyond the radius.


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## homebrewed

One of the advantages of using OpenSCAD is that it makes it relatively easy to change the model.  In the case of changing the tool bit angle, I just had to change "-12" to "12" in a command that rotates objects.  So:





Changing the angle does provide more "meat" for a set screw.  This angle also makes more sense to me since it should direct chips outward.  Good one!

I also was an electrical engineer (actually, probably always will be).  But in my line of work -- Failure Analysis -- I often found it necessary to improvise or make my own tools.  The market is so small that few companies make stuff for the discipline, or, if they do, it's very expensive.  So there was a lot of motivation to become a toolmaker.


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## courierdog

That is interesting. I mostly worked on RF Design of Filters and Antennas in the very early days of what became Cellular Radio. Today, the antennas are a direct extension of a fibre optic cable and DC power. What used to house the Radio equipment and network communications is now just power supplies and the fibre optics is 100% passive back to the Central Office.
Like you I found during my time any specialized tooling was hacked together by "Butchers" on an as required basis. The excuse given at the time well it is only a one of. I disagreed as there is no such thing as a single "One Of" circumstance. I built jigs for everything I made. Even drilling templates I found were repeated many, many times over.
Back to the Fly Cutter.
Yes, you hit the nail on the head, with the tool facing outwards, the chips are moved away from the work piece and carry the heat with it. I tried the concept put forward by Mike where he has the tool bit facing into the work and the chips tended to stay close in onto the work, increasing the heat at the cutting point. 
Turing the cutter outwards as Gary illustrates in his Diamond Tool Holder FlyCutter approach allows for the chips to be spun off in an outward direction. In this case a containment or perhaps a suction means of clearing the chips in a controlled manner.
Chip control is a concern on the Mill, as it does have a tendency to fling chips every where.
Different issue.
Now that we have a working drawing (illustration) 
I am thinking, (That may be debatable) 
Cut down the middle of the implied Tool Bit.
The drilled hole for round Tool Bits
A milled channel on either side for the use of Square tool Bits
From Gary Sneesby (Eccentric Engineering) us a "Vee" rather than a square to enable tighter clamping
I would attempt to have two holding screws 
First one near the tip above the protruding cutter
Second further back and below the cutter
Using the downward defection of the tool bit to find the optimal place meant of the two screws.
There should be, as Gary Suggests no need for a back stop adjustment approach, if the clamp is designed optimally to hold the tool bit in place.
I have west to experience any push back using the Diamond Tool Holder on my lathe as some claim.
Taking the Diamond Tool Holder clamp off reveals in is not just as simple as it appears on the outside.
One could use the Removable Clamp Piece from the Diamond Tool Holder, except the clamping screw would now be under the Flywheel.
In the Flywheel FlyCutter concept, My mind just does not want anything below the flywheel except the cutter.
There would be the, (however slight) an implied threat of a loose screw under the Flywheel.
OK it is time to here back from you on this interesting topic.


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