To make a long hole hex broach out of a allen wrench is easy and they work realy well. A 3/16" or 1/4" for example you cut a series of grooves 3/16" wide just
to the flats. Leave the hex between each groove 1/8" wide. Make about 10 of them. Now turn down the hex at the tip to .002 dia larger than the grooves you
just cut. Go to the second one and turn it .004" third .006" ect. The grooves are for chip clearence and make the cutting edge, the amount of them is how
many it takes to get back to full size hex. Then you just use your tail stock to push it thru your hole against the chuck or a face plate. With soft stock you
don't need to re-harden it. I have made other custom shaped broaches as well.
Have a nice Christmas,
Take Care,
RICK