View Full Version : Deep hole broach?

07-22-2006, 11:03 AM
I was reading a book about double rifles. One aspect of the manufature is very unclear to me, how do they make the rectangular hole for the cocking arms in sidelock guns!?

The hole is very deep, maybe 2" or so! I goes right thru the bar of the action. How deep can a broach cut?

07-22-2006, 11:27 AM
I guess it depends a bit on how big a broach! I've done broaching deeper than the intended for the broach/bush and its not a problem - but you have play with make different bushing/shim combo's The main problem with a deep broach is its cutting on many more teeth than a shallow broach at once - a big increase in cutting force that'll snap the broach. So engineer the depth of cut by the depth of the slot in and work out the different shims you need so that each pass has is removing less than what it would be cutting across the length of a standard bush/sleeve

07-22-2006, 11:45 AM
10x5x55mm is the hole i would guess?

07-22-2006, 12:14 PM
wow that is small, and rectangular. and long :D. guess the bushing/shim part isn't applicable. Out on a limb a bit as i don't know how this specific piece is actually done, but if you were to broach it, the broach would have be designed such that it in any 2" length, it was only removing the amount of material that it was capable of without busting. it other words you end up with a very long broach with each tooth removing very little material. When broaches get very long and thin, you can't push them, but have to pull them, the ones i've seen were set up horizontally. if this is a 'how do i do it' question, an alternative would be break that long broach down into a set of progressive, shorter broaches that you could use on an arbor press. I've made homemade broaches for square holes and they do work, but they're a lot of work to make and you'd have to stretch the whole idea out to work with that depth.

07-22-2006, 12:17 PM
"How deep can a broach cut?"

Don't know enough about guns to understand the part you're describing, but broaches can do an almost unlimited depth (if it's a through hole). They use pull broaches rather than the push type commonly used for keyways in pulleys, etc.

Long broaches with many small teeth taking tiny cuts. No shims, job is done in a single pass.

07-22-2006, 12:20 PM
Yes it would be a veeery long broach!

I was dreaming up some alternative ways and one would be to file it in a fileing machine. If one had one of them that supports the file in both ends, that could work!?? But i really have too little experince in this to know. I just find it very impressive to make a such deep rectagular hole!