Here's what we learned this year for feeds, speeds, depth of cut, bits, and cooling-
On our CNC router (4x8 foot shopbot with 18k rpm spindle), we used
this .250 onsrud aluminum bit. We went full DoC on our .125 aluminum, at 90 ipm with the spindle at 13,000 rpm. We sprayed some coolant (
Mobilcut 102), and had compressed air too.
On our CNC mill, we mainly were cutting .250 and .500 aluminum plate, so we used a .250 diameter three flute endmill for
aluminum. We also used it on steel once, and it didn't break. I believe we got the one with the TiCN coating.
With a .100 depth of cut, and the spindle at 5100 rpm, we went between 12 and 16 ipm. Our finish pass (.015 wide) was at full depth at 8 ipm. It is important to feed very slowly if you're going straight into the part. If there's enough room, do a helical plunge. We use flood coolant, which does an awesome job of clearing chips out of the way.
A few tips for accuracy- your hole diameters will only be as accurate as your endmill diameter is. We use a bunch of reground endmills, and precisely measuring their diameter is really critical. To measure bits with three flutes, you can make a little slotted hole with the bit, then measure that. Doing a slow .015 wide finish pass at full depth going nice and slow leaves a great finish, and a super accurate diameter. Our accuracy for making 1.125" holes with our .250 bit is within 3 ten thousandths.
Using good tool holders is really important too. We used a drill chuck for our edge finding bit, so our indicated edge locations were only as accurate as the drill chuck, which I measured to have about .006 runout. This end up causing a very misaligned shaft.