"Pete C." wrote in message
ter.com...

PrecisionmachinisT wrote:

wrote in message
...

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.


I would be concerned trying to do this on a CNC mill unless you can lock
the spindle brake, otherwise the bit could rotate as you try to use the
mill as a shaper. I also think you will find you don't have a way to
index the spindle to the orientation you want.


There is no need to index if you use a square tool that has back-taper
ground on all four sides--also very little rotational force is generated if
you are cutting two corners at the same time and so as long as there is some
sort of cam that locks the spindle during M19 you'll be fine.

I think you would be much better served putting a cheap X-Y table under
a manual arbor press and doing the pseudo-shaping that way, or just
getting 30% lowers to start with.

A single axis slide under any industrial quality post drill will work, too.