Broaching Question

[epanzella]

Can I broach a keyway in a hole that's deeper than the broach bushing length? If I can, how much unsupported broach can be tolerated? I guess if the answer is no unsupported broach then I'd have to make a new bushing, right? (new broach set - never broached before)

 

[woodchucker]

I don't believe you can. The broach will break. You might get away with a small difference, but I'm not sure what it is.
The back of the bushing (and shims) are what keeps it cutting, after that, I'm sure it wants to bend (which it won't). And the broach is hardened, so more prone to a clean break rather than a bend.

 

[snoopdog]

Best just to make another bushing, cheaper that way.

 

[benmychree]

The answer is maybe; it would depend on the amount of overhang and especially the amount of overhang. In steel, I would not worry over 1/4 - 1/2" of overhang, have done it many times, but it would also depend on the size/ width of the broach, the smaller the size, the less tolerant of overhang. In my shop, I made the question moot by buying and overhauling a Mitts & Merril keyseater., capacity from 1/8 or less in width -1 1/4" and 12" in lingth.

 

[benmychree]

Best just to make another bushing, cheaper that way.

Perhaps longer bushing helps, but longer shims would also be necessary, and even then, chip overload would be an issue, especially with smaller broaches, which would tend to buckle sideways and possibly break, been there seen that.

 

[tq60]

Just a thought...

A deeper bushing for support.

But cut the slot at an angle where the slot is deeper in the bottom than top.

2 will be required, second one, finishing bushing is straight.

This would cause the broach to cut at top like normal but not cut much at bottom.

Reduces chip load.

Once finished with the angled cut the straight bushing is used to get the bottom.


Holding it for pressing is a challenge, a support could be made
Sent from my SM-G781V using Tapatalk

 

[epanzella]

I think I'm gonna side step this whole issue by shortening the part to be broached. The bushing is only 1/4" short so I can machine off the boss I left for a set screw. I'll just put the setscrews in the roots between the teeth. It's a worm so the first and last tooth won't have full engagement anyway.

 

[MrWhoopee]

The part being only 1/4" longer, I wouldn't worry about it. For longer parts, if permissible, a hole can be drilled about midway in the part, in-line with and a little larger than the keyway to allow chips to escape. Care must be taken to ensure that they do. I've broken a broach or two, not fun.