"Grant Erwin" wrote in message
...
wrote:

2-flute for slots, 4 flute for when you want higher feed rates (keeping
the advance/tooth constant, the only way you can up your feed is by
adding teeth).

I don't buy the steel/aluminum answer, sorry.

I agree that just saying 2 flute is for aluminum and 4 flute is for steel is
not a correct answer. But I think it is correct in a way.

Because aluminum is (typically) quite a bit softer than steel, one can take
very aggressive cuts which leads to larger chips. These larger chips need
more clearance which is a characteristic of 2 flute endmills.

Just to put my own "me too" in, I use 2 flute cutters when removing a lot of
material, or making a feature which does not allow for (easy) chip removal -
slots and pockets. I use a 4 flute for finishing because of the doubled
feedrate and light depth of cut.

Also, I find 4 fluted cutters to be more stable (less deflection). I think
this is because they have more meat, but that's certainly just a guess.

As far as really practical advice, I'd want a good selection of 2 fluted
cutters in my box, while having an odd 4 flute for times when I'm doing a
lot of finishing.

Regards,

Robin