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Any inexpensive ways for making square holes? 1/4" x 1/4" to be exact.
Current thinking is to just use a round rod and machine the square on
the drive end. But then how do I stop the "prongs" from rotating
around a round rod. There is a reason they used a square rod. {grin}


The classic way is to use a lathe--drill a 1/4 in hole then stroke it out
with a shaper that you've made out of a 1/4 drill blank.

BINGO!, great idea I didn't know. This is why I wade through all the
flotsam on RCM, I get a gold nugget every now and then.

PT, would I dare put a "D" shaper bit like this in my CNC mill and
cycle the Z axis to shape out a square hole?


Normally I would use a slightly different form and index 4 times but you
could also make up a square tool and get away without having to index at
all.


One step farther, I'm building AR15 lowers and the magazine pocket
needs to be nearly square. Use this idea in the CNC mill to finish the
corner?


Yup...mill a bit oversize first and then chop the corners away using a form
tool.