It's begun....

[Jonathan]

Assuming that's a 6mm cutter, then the feedrate and speed you posted should be fine. With only 30% stepover you could actually increase the feedrate slightly due to chip thinning, but I'd leave it for now. I tend to agree that rigidity shouldn't be a problem.

You're problem is almost certainly the lack of coolant. Air will help to cool the cutter, but not much compared to coolant (i.e. mainly water). Also, with no lubricant the co-efficient of friction is greater, so more heat is generated. You'll probably find that even a small amount of coolant will do the trick, or if you've not got any then WD40 works well on aluminium. I certainly wouldn't advise using it regularly though as it wont be good for the bearings.

If you think the rigidity of the machine is a problem, as a general rule don't change the feed or speed, instead lower the depth or width of cut. The reason is if you've chosen the 'correct' feedrate and rpm, then the chipload will be a particular value which you want to maintain. If you just change the feedrate or the spindle speed the chipload will change.