Terry wrote:
I am making some aluminum lens holders for an old 1940's camera. The
original was basically a stamped piece of .054 alluminum approx 4"x4"
with the side walls being about .2" high. Then a hole was punched out
for the lens.

I have made a few of these so far on my cnc mill and they have worked
out great. But since I am still learning about cnc machining, I had a
question that I have not been able to figure out.

When I am making these parts, I am starting with a peice of .200 thick
aluminum. I first pocket out the center, then cut out the hole, and
then finish off by cutting out the outside edge. The only small
imperfection (which doesn't effect performance, but annoys me) is when
I am pocketing the final depth, I always end up with a ridge on the
bottom surface which is the thickness of the cutter away from the
sidewall.

Basically what is happening is when it is cutting that last .002 off
the bottom (my finsihing pass), it is also cutting a small amount on
the side walls. It looks as if the side cutting action is effecting
the bottom cutting action. I am 'chip cutting' so I don't know if this
is what is causing it. But it seems to always cut about .001 deeper
along the side walls than the rest of the pocket. The rest of the
pocket is perfectly smooth.

I have tried pocketing from in to out and out to in. And have tried
using a finish pass, and without a finish pass, but I always get that
little extra depth when cutting along the side wall.

Anyway, if anyone has any pointers please let me know. I hope I was
somewhat clear in my explanation.

Thanks.

I've used a reverse spiral fluted right hand 2-flute end mill... the end
mills flutes cut to the normal direction but the flutes spiral to the
other direction.... so when you're cutting side walls the force pushes
down on the part.
Jack

p.s. its been 10 years since I've seen one, but they make them.