View Full Version : Broaching

01-24-2006, 10:13 AM
I need to broach a 3/32 keyway through a 3/8 bore in the flywheels on my Ajax steam engine. The broach bushing is about 7/8 long and the hub is 1 3/8 wide so.....I first thought about buildind a longer bushing then thought why not just get another bushing and put one in from each side and line them up with a piece of keystock. Is this a sure way to break my broach or will it work? Material is cast iron.

J. R. Williams
01-24-2006, 10:26 AM
Care must be taken with the small broach as the depth maximum is the length of the pilot bushing. One way out is to machine a new pilot bushing the length of the hub and make the slot deeper to reduce the depth of cut on the first pass. Move to the required depth in several steps by using a series of shims. This will reduce the chip load on the broach. I have done this and used brass for the pilot.


01-24-2006, 11:31 AM
Maybe it's just my daring nature, but I simply poked the broach through from one side (using a 1/8 pin to finish the push) and then did it again from the other side. The depth of the cut on the unsupported side was a bit lower but the second pass cleaned it up just fine.

01-24-2006, 12:44 PM
I broach a bunch of small gears and sprockets, 3/8" to 5/8", for a High School FIRST Robotics team - - mostly in cast iron. I have found the best way is as JRW said - - make a new bushing with a slightly deeper slot, cut the first pass and then shim up for a second pass. While I have been lucky and gotten away with a shallow bushing a few times I have also had the broach bend and dig in at the top and/or break. If you only have one to do then it may be worth a try but making a bushing isn't that hard and a new 3/32" broach is $35+ and I can't run down to Ace Hardware and get a new one.


01-25-2006, 09:14 AM
I think since it will only take a few minutes to make a longer bushing with a deeper slot I'll give that a try. Thanks for the assistance.