oldvan wrote:Is HSS a better choice for aluminum?
Depends. If chip welding is an issue, there are available HSS end mills ground expressly for aluminum. They are polished, and have greater relief. Lube for the cut would still be advisable, however.
Deep depths of cut should almost always benefit by the use of carbide, if for no other reason, carbide is much "stiffer" than HSS. That would not be true if the machine in question is not robust, however. Any transient movement in carbide machining tends to destroy cutting edges.
Stiffness is why solid carbide boring bars are so popular. Cuts that border on the impossible with HSS can be taken in stride with carbide bars. I expect that you can achieve much the same results with end mills. I can think of no personal experiences to verify my opinion, however.
Part of the problem with comparing carbide against HSS in lathe work is that carbide insert tooling can be negative rake, which is completely different from machining with positive rake. Negative rake inserts are generally not ground, so the resulting surfaces are not as smooth as diamond ground positive rake inserts. That would not be true of carbide end mills, which are, today (thanks to CNC cutter grinders), ground from solids, so the resulting surfaces are relatively smooth, and should yield acceptable results in lowering chip welding. The added stiffness would certainly be a great benefit.
Harold