On Jul 18, 6:27 pm, "David Anderson"
wrote:
Any ideas how to machine a 0.250 x 0.250 inch square hole in 1/4 thick
low-carbon steel (only two required). Tolerance minus zero plus 0.002. Begin
with a drilled hole. I have a die filer also a small shaper but a good set
up seems unlikely. Maybe a home-made broach? Thanks for any ideas.
Dave

I've often thought about making up a toolholder for my shaper that
would allow mounting a bit in line with the ram movement axis. You
could use, say, a 3/16" square bit and feed it into the corners.

For a hole that small in mild steel, though, you can probably get away
with drilling the corners, then drilling out the center, and then
forcing through a 1/4" tool bit with a press or with a hammer. Grind
the tool bit straight across and sharp, or even better with a bit of
back rake. Might have to back up the workpiece to keep from blowing
out the edges.

I've also considered chucking a tool bit into a spin index and then
using my surface/T&C grinder to grind the end of a tool bit to round,
and extend the round back along three corners - thus making a broach
which would cut one corner at a time and thus be a lot easier to
drive. Then one with two corners for the second pass, etc. For a
tool bit of only 1/4" I'm not sure it would be necessary.

John Martin