"Steve Lusardi" wrote in message
...
The previous responses were general, but not absolute. You can use 2 flute
on steel and there are 4 flute end mills that plunge. It is all about chip
clearance really.
Steve

Nope. It's about relief angles, which are the real limiting factors if you
expect good tool life and good cutting performance. Chip clearance is not to
be ignored, however. Properly ground 4 flute end mills applied to aluminum
would likely suffer from chip clearance problems with considerable loading
of the flutes, often leading to broken end mills.

Harold