[Jared]

I just got back from cutting 0.25" aluminum plate on a Tormach PCNC 1100. We used a 1/8" and 3/16" two flute endmill. Like Cory said, we started with 12.8 IPM from G Wizard, but we got a bad finish on some of the bearing holes, so we slowed down to about 8 IPM, and got a great finish. It's hard to tell in the picture, but we got a pretty rough finish on the part. You could probably use the 12.8 IPM for roughing, then take a final pass with a really small cut width as a finishing cut. When we slowed down, the little scrape marks from tool deflection went away. It's also really important that you get the coolant on the actual bit.

Also, you should definitely slow down the plunge rate. We had 6 to begin with, and broke a 3/16" end mill, and we were fine once we brought it down to 4.

I also agree with your opinion of MasterCAM, but once you get used to the silly setup, it's actually really powerful. It'll automatically do all sorts of cool stuff, like tabs, finish cuts, and depth cuts for you. I do agree that it's not perfect though, the command "regenerate all dirty operations" isn't exactly obvious.