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.