Have a look here where I milled some of the strongest grade of aluminium with the 3040 and 200watt air cooled motor. http://www.mycncuk.com/forums/showth...ll=1#post30109

It was damn slow, so to be honest the 3040 is not up to it, although I did some softer grade 6mm thick aluminium with reasonable success and at 200mm/min (1mm pass). Given how my 3040 does, I'm reaosnably sure the 6040 with a 1.5KW motor would do pretty well unless you need high speed or very high tolerance.