# Lathe broaching a keyslot



## stomp10 (Feb 11, 2019)

Using Mr Pete's you tube video on this:





I happen to have a blank of both what I call tool steel or, I can use the other end of an HSS parting tool.
I tried it with a blank 3/32" HSS bit but it had WAY too much flex as it was pressed into the piece. And still not wide enough to make a 5mm keyslot.
I want to use the tool steel blank to make the cutter as it should have a lot more rigidity than the HSS.
The tool steel is super hard to my mind. 

(Dont laugh.... ) 
I ground down an old Armstrong knurling tool clamping tang so it would fit into my Enco stock toolholder.  It took FOREVER!!! But it also allowed me to creep up on the final grind dimensions.  That old knurler looks pretty cool now too.
It also seems to me that this stuff is super rigid.
This is why I want to use this blank instead of the HSS one but, I have no idea if this will work for the cutter as I have never heard of this being done. 

Can I use the Tool steel or should I stick with HSS for making the cutter?


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## JimDawson (Feb 11, 2019)

stomp10 said:


> Can I use the Tool steel or should I stick with HSS for making the cutter?



HSS didn't exist until after the turn of the 20th century, around 1910, and wasn't in really common use until the 1930s.  Before everything was tool (high carbon) steel.  Yes, it will work fine.


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## stomp10 (Feb 11, 2019)

Wow, That makes perfect sense, Jim.
Lots of messy black nasty powder in the process.
This from My Grandfather's tool box, so the time frame you mention fits perfectly.
all his ground bits in the drawer are HSS which would have been early to mid 20th century for his working years. A remnant from his apprenticeship perhaps.

Not expecting ANY problems cutting this slot!
This is for the DC motor upgrade pulley on the lathe, so I can't wait!

Thanks a million for that answer!


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## benmychree (Feb 11, 2019)

Do not worry about using hard steel for non cutting tools. ridgidity depends on modulus of elasticity, heat treatment and alloy have nearly no effect on modulus, only carbide is stiffer than HSS, you could use a HSS tool bit in a soft steel boring bar to cut keyways.


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## stomp10 (Feb 11, 2019)

Ben, the boring bar method is actually my plan B with a single tooth cutter, as to me grinding the cutter seems an easier solution based on my meager shop. Until I get the drill\mill thing running again I am quite challenged in drilling holes for a boring bar.  I am hoping to change that soon though.

I'll have to take your word on what you just said as understanding the modulus of elasticity is way outside of my wheelhouse.

Its hard to believe that HSS and tool steel have the same flexability cuz in my hand tool steel just feels harder\stiffer. I realize that isn't any reliable test, but just my feel for it.
I'll gladly soak up any shreds of wisdom anyone wants to share though.
Is there a way to briefly describe what that is for me?


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## P. Waller (Feb 12, 2019)

These tools are available as inserted tooling, you will not have to stop it every 10 parts to grind a HSS tool.





						Rev Broaching Tool - Home
					

New patented tool system for broaching and slotting processing on lathes, milling machines and cnc workstation, with symmetric adjustment. Ideal for traditional slotting machines.




					www.revtool.eu
				




If you have a live tooled lathe then this will broach from the turret. This is for low production/prototype work as no manufacturer would actually produce parts in this manner.

In the past I have produced blind internal keyseats with a manual lathe, this is the exact opposite of "efficient". 

If however you choose to do so here are a few tips, drill a hole from the outside of the part to the bore at the end of the keyway, this is where the tool will stop without hitting the back of the last cut. I realize that this hole may ruin the appearance of a part but must be done.
Lock the spindle if your lathe does not have a C axis drive, placing a manual lathe in back gear is not enough so you must find other means of locking it.
Good Luck


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## WarrenP (Feb 12, 2019)

Very interesting broaching tool.


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## stomp10 (Feb 13, 2019)

Warren. this thing is amazing.
Who said German engineering is dead?
Thanks for sharing that!
Apologies... P.Waller... I thank you!
Trying to read without my glasses again.


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## P. Waller (Feb 13, 2019)

I suspect that there is a limited number of home machinists that have live tooled lathes that will operate such a device (-:

I could be wrong however, Grizzly may have a line of live tooled turret lathes that they keep a secret.


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## JimDawson (Feb 13, 2019)

P. Waller said:


> I suspect that there is a limited number of home machinists that have live tooled lathes that will operate such a device (-:



My lathe would, but I suspect there are not many others.


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## vtcnc (Feb 14, 2019)

There is this option as well:

Punch Broaching


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## stomp10 (Feb 14, 2019)

vtcnc,
Awesome! I've been trying to work out a way to do octagon cuts on the lathe in my head.
This is def a possibility.
Thanks for sharing that!

And thinking about other possibilities.... WooHoo!


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## Cobra (Feb 14, 2019)

if it's any help, this link shows the broaching of some pulleys for a project.
The holder is from O1 steel and the cutting tool is ground from a broken endmill.









						Tool Post Grinder
					

I have been building some small engine models and particularly when doing the pistons and cylinders thought it would be great to have a tool post grinder.  Well, I didn't like the price for one so decided that it would make a good project.   Using one of the Wrokshop series of books on spindles...




					www.hobby-machinist.com


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## stomp10 (Feb 16, 2019)

Great write up, Cobra. You do some nice work!
In your shots it looks like that broach face is 90 deg to the cut with a little bit of relief ground on the contact face? Is there a rule of thumb for grinding these?
I have ground mine at about 7 deg. I haven't yet made the cut. Maybe later this afternoon if I have time.
I hope it works as well as yours did....
I also have only about an hour a day most days to devote to my hobby, so my learning process is pretty slow at this time....


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## Cobra (Feb 16, 2019)

stomp10 said:


> Great write up, Cobra. You do some nice work!
> In your shots it looks like that broach face is 90 deg to the cut with a little bit of relief ground on the contact face? Is there a rule of thumb for grinding these?
> I have ground mine at about 7 deg. I haven't yet made the cut. Maybe later this afternoon if I have time.
> I hope it works as well as yours did....
> I also have only about an hour a day most days to devote to my hobby, so my learning process is pretty slow at this time....



Hi Stomp10.
I don't know if there is a proper rule for the relief but I ground the endmill shank to 5 degree relief on both the face and the sides of the tool.
As I said, it worked OK if you take LITTLE bites.  The first try just bounced off the pulley!  Once I reduced the bite to about a thou or two, it went much better.  The tool is ground to give a finished 0.125 keyway from the initial set up.  I didn't want to attempt to re-set the height up and down to get the finished size on the keyway.
If I can provide any more help, just give me a PM.  I am certainly no expert but would help where I can.
Jim


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## stomp10 (Feb 17, 2019)

Thank you Jim, I really appreciate that.

This slotting project worked out really good in the end.
Got the tool ground, set up in the lathe, set a first depth of cut, ran the saddle into the cut and got scrapings from 2 sides of the arc.
So far so good. Took a few more cuts and the cutter never seemed to get past the arc.  Wanting a result i advanced it to what I knew would be too deep of a cut and put some torque on the saddle wheel. Discovered all kinds of places from the saddle to the toolpost where movement is evident.
Gonna have to run them all down eventually.
Right now I need a slot, and sure glad I used tool steel for this. I went caveman on the rest of the cut.  I cant see HSS surviving what I just did to that poor cutter.  But now I have a straight, tight slot in my pulley with no slop. And it still slides on the shaft. Got the motor mounted and running again in no time at all.


Totally thrilled today!
Thank you everyone for sharing!
Brad


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## gwelo1962 (Apr 14, 2019)

A friend of mine has done a bit of this. His advice was if your lathe is small/light(9"SB) "pull" the cutter out, not pushed in towards the headstock.


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## benmychree (Apr 14, 2019)

stomp10 said:


> Ben, the boring bar method is actually my plan B with a single tooth cutter, as to me grinding the cutter seems an easier solution based on my meager shop. Until I get the drill\mill thing running again I am quite challenged in drilling holes for a boring bar.  I am hoping to change that soon though.
> 
> I'll have to take your word on what you just said as understanding the modulus of elasticity is way outside of my wheelhouse.
> 
> ...


There is a demonstration of it in the book "Tool Steel Simplified", they have heat treated and soft steel clamped on one end, and hang equal weights on both, and they deflect equally until the elastic limit is reached, and the soft steel takes a permanent set (bent).  This is why a hard boring bar is no stiffer than a soft one.


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## stomp10 (Apr 23, 2019)

Thanks Ben, that actually makes sense to me now.

Gwelo, I have taken some time to eliminate as much flex in the cross slide as possible and working on finishing up mounting a nice new Bostar  wedgie tool post on the crosslide. I figure this is the best way to go for the sake of ridgidity.
I'll do a donut mount for the crosslide and keep it around and use it for taper cuts.
And it is indeed an Asian cheapie lathe, I am enjoying the process of making it better than it was though, and seeing what I can make it do.  (It was posted in my signature, but for some reason that isn't displaying-something else to figure out. lol)

I have another pulley I need to make, so I will def try dragging the cutter through the slot. I'm expecting much better results this go around.  I'll post my results once I get that far.  May be a while, life does get in the way....

I appreciate everyone's help, suggestions and explanations though... Very much so! You guys have all helped me out in many different ways!


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## SnakeyJ (Apr 23, 2019)

I was keying some 1/8" internal slots on some 5/8" collars last week - I used an HSS parting tool blank, but I did break it twice keying three collars.



gwelo1962 said:


> A friend of mine has done a bit of this. His advice was if your lathe is small/light(9"SB) "pull" the cutter out, not pushed in towards the headstock.



^ Definitely good advice here, though much easier for keying external slots.  You might need to spend a little time at the grinder to make a tool for internal slotting on small bores.


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## stomp10 (Apr 23, 2019)

stomp10 said:


> Thanks Ben, that actually makes sense to me now.
> 
> Gwelo, I have taken some time to eliminate as much flex in the cross slide as possible and working on finishing up mounting a nice new Bostar  wedgie tool post on the crosslide. I figure this is the best way to go for the sake of ridgidity.
> I'll do a donut mount for the crosslide and keep it around and use it for taper cuts.
> ...


I'll do a donut mount for the crosslide and keep it around and use it for taper cuts. (make that the compound slide....)


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## gwelo1962 (Apr 24, 2019)

Next time perhaps you could mark things out and drill out some of the keyway before boring.


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