unfortunatly, the nature behind your setup is that you are going to wind up breaking a few (lots) endmills. While alum is a very forgiving material to cut, small endmills are not. About all I can suggest is to wind up you drill press as fast as it can go (RPM) & try to control your depth of cut to very small cuts. I am talking like .01" (.25mm). this helps a few things...heat does not build up as fast & the chips clear out easier (much smaller chips) Feed the bit through the piece as slow as you can stand to turn your handle. Try & keep the chips flush out from the cut as best as you can. It might take forever & a year to cut 1 channel, but the walls will be vertical & your bit should hold up longer. For cutting fluid on both alum & copper, try kerosene. really. The stuff works better than anything I have ever seen on alum, plus you get to inhale the fumes as a bonus
. Try using a squirt type oil can & flood the shit out of the part with the kerosene, this should help flush the chips & keep the heat from building up also.