pic: 4 inch Wheel Render

[artdutra04]

Originally Posted by Akash Rastogi

Hey Art,

Could you elaborate on the proper way to do this? Sounds very interesting. Thanks.

My roommate did this to broach some aluminum parts for a combat robot he was working on.

What you do is take an old HSS end mill, and cut off the cutter portion of it, leaving just the shank. Then mount this in a collet in a lathe with cut off end of the end mill sticking into the lathe, with the original end sticking out. Crank turn on the lathe, and then hold a Dremel with a cutoff tool perpendicular to the end of the end mill, and slowly turn the entire end of the end mill into a concave dimple.

Then get a large piece of steel hex stock, mount it in the lathe, and bore a through hole the same diameter as the end mill. Mount this piece of hex stock in a milling machine and drill/tap holes for set screws to hold against the flats of the HSS end mill shank.

Then mount the HSS end mill shank into the hex stock, and make sure the set screws are against the flats of the end mill, with the dimpled end sticking out. Then go over to the precision grinder and stick and steel hex stock on it, and activate the magnets to keep it in place. Now use the precision grinder, which should have a XZ table. Slowly start grinding down a flat into the HSS end mill. Once you've started this, deactivate the magnets, turn the steel hex stock by 60 degrees onto the adjacent face, and again grind down a small amount.

Don't adjust the Z-distance until you've done all six faces; it helps to mark one with a Sharpie/some mark, to make sure the hex stays true. Keep going, grinding down all six faces, then readjusting the Z, and then again grind down all six faces until you reach the correct size hex you desire. Now you have a homemade HSS hex broach. To use, simply first bore a round hole to the diameter you want in a lathe, then mount the HSS hex broach in a lathe and use then force the homemade hex broach through the round hole (while the lathe is stationary of course).

It might take an hour to make your own hex broach, but for broke college students, it sure beat spenting $$$ to buy one.