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Anyone know what these are and how these are used?
- Thread starter YYCHM
- Start date
trlvn
Ultra Member
Building on @RobinHood 's question, what is the geometry of the cutting edge? Maybe if it had more back rake, it would dig in more and not leave a rising ramp? Although, too much back rake might make the cutter dive in too deep and break! That is a lot of extension forward of the toolholder compared to the cross section of the cutting bit.
If it was sharper, shouldn't you get longer curly chips rather than the crumbles shown in the pictures? I imagine that you shouldn't hone the sides of the tool since that would alter the width of the keyway produced. The end and the bottom should well-polished though.
Craig
IIRC, there is quite a dish on the bottom of the tool. Not the easiest thing to hone. Perhaps a very fine mounted rounded stone on a Dremel would work. A regular flat surface hone does not reach inside the dish.
I think Stefan Gotteswinter used a small cut-off wheel in a Dremel, while the tool was turning in the lathe chuck, to dress the dish on a broach. It was in one of his videos a few years back. Might be something to consider.
Dished on the bottom???
Dabbler
ersatz engineer
Your tool was cut on a bench grinder leaving behind a small radius. It is preferred the bottom be a ramp, instead of a curve.
The clearance angle should be only about 5 or 6 degrees on a keyway cutter - NOT the 15 degrees some very popular (but wrong) youtube creators use. The cut depth should be in the order of .002 one each stroke. (for HSS cutters)
The leade angle on the tool depends on the material - it looks like you were cutting cast iron. For that I'd use about 8-10 degrees. For cold rolled steel, about 6 degrees is better. For softer things like aluminum, 1 or 2 degrees of leade is all you need. For copper and brass, a negative leade of 2-3 degreeswill stop the tool from diving into the work. - all at a clearance angle of 5-7 degrees.
The clearance angle should be only about 5 or 6 degrees on a keyway cutter - NOT the 15 degrees some very popular (but wrong) youtube creators use. The cut depth should be in the order of .002 one each stroke. (for HSS cutters)
The leade angle on the tool depends on the material - it looks like you were cutting cast iron. For that I'd use about 8-10 degrees. For cold rolled steel, about 6 degrees is better. For softer things like aluminum, 1 or 2 degrees of leade is all you need. For copper and brass, a negative leade of 2-3 degreeswill stop the tool from diving into the work. - all at a clearance angle of 5-7 degrees.
x2 what John says.
If you look at the bottom of the broaches carefully, you will see that they are not flat. They have a concave depression (they are dished). That is on purpose with those cutters. Because they are not flat, you can’t just run the bottoms on a honing stone - it will not touch up the cutting edges properly. You need another method - hence my reference to a Dremel with a cutoff disc and the tool rotating in the lathe spindle. This is to re-create the dish.
To preserve the true geometry of the cutting edge, a much more difficult grind of the bottom is needed. It is almost impossible to do economically, thus everybody just uses the dish method and calls it good (which it is for small angles, like 1 or 2*). Stefan G. also makes that comment in the video I referred to above (wish I could find it…)
If you look at the bottom of the broaches carefully, you will see that they are not flat. They have a concave depression (they are dished). That is on purpose with those cutters. Because they are not flat, you can’t just run the bottoms on a honing stone - it will not touch up the cutting edges properly. You need another method - hence my reference to a Dremel with a cutoff disc and the tool rotating in the lathe spindle. This is to re-create the dish.
To preserve the true geometry of the cutting edge, a much more difficult grind of the bottom is needed. It is almost impossible to do economically, thus everybody just uses the dish method and calls it good (which it is for small angles, like 1 or 2*). Stefan G. also makes that comment in the video I referred to above (wish I could find it…)
B&S MFG CO.
PROV RI U.S.A.
Long gone I'm afraid......
I've seen B&S mentioned on the site before but I can't recall in what context?
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