Make Square Holes with a Square Bit

[Crusty]

Thanks, and BTW the broaches can be any shape that you can grind a cutting edge into, hex, octagonal, etc. I used square because I already had a ready made blank to start with and that shape does the job I needed it to. For a hex broach you might be able to start with an Allen wrench if you can harden it. You can find used adjustable tool holders on Ebay for not too much and they save a lot of time in construction.

One thing I would do differently is to capture the bit so that it can be withdrawn using the lathe or mill that it's mounted in because the simple way that I made mine means that I have to use vise grips to get the bit out of the work afterwards.

A couple of more details: Drill your bulk removal hole diameter 100-103% of the distance from flat to opposite flat and countersink it a bit before broaching. Run the lathe or mill at a relatively high rpm.