Stumped - Cutting a square with a rough and finishing cut

[loedward22]

The part I'm cutting is basically a square. The material is 1/4" thick 3003 Aluminum and I'm using a 1/4" two flute end mill at 3050 RPM and 13 IPM. The program is coded to do conventional milling on the roughing cut, which starts in the upper right corner and works counter clockwise, cutting the outside of the blank away. Then the finishing pass is .005" on all edges with climb milling starting in the lower left corner and working clockwise. the problem is that on the finishing cut it's only removing material from 3 of the 4 sides. What could cause this problem? I've banged my head for over a week on it and have considered back lash, movement in the table, movement in the work piece, movement in the cutting tool, but nothing makes sense. The problem is repeatable and to get the 4th side correct I have to take .03" so it's off quite a lot. Any ideas?

[kling8]

I would leave more material for the finish pass, I usually leave .01-.015 on aluminum. I would also conventional mill both roughing and finishing, and use a carbide endmill made for aluminum.

[Starleper1]

I would not conventional mill at all. Generally in CNC you climb mill everything. Simply because it gives a much better finish which I hope you already know.

[Superman]

Originally Posted by loedward22 The program is coded to do conventional milling on the roughing cut, which starts in the upper right corner and works counter clockwise, cutting the outside of the blank away. Then the finishing pass is .005" on all edges with climb milling starting in the lower left corner and working clockwise. the problem is that on the finishing cut it's only removing material from 3 of the 4 sides. What could cause this problem? Any ideas?

Cutter flex on the 1st move as it is cutting 100% width of the tool

1st try raising the RPM or slowing the pass diong the 100% width of cut

Either Zig-Zag area clear your pocket leaving 50% of the cutter diameter on the walls ( quickest method ), or spiral from the center out
then profile climb-mill the walls leaving 0.005", then finish profile

PS put your RPM up lots and lots and lots, feed approx 0.0015"-0.0035" per tooth, hold tool short as possible ( use coolant, coolant/air mist, or air--- in that order )