Mechanical Magic wrote:
What Jon said,
BUT, with more emphasis on chip loading of the tool.
Peck .05" in Al, if it packs up you have a problem.

No recs on downfeed rate, it's too dependant on the grind of the end
mill, some brands/sizes downfeed great, sometimes a lemon. To me
center cutting end mills are a mystery. If you find a good
combination stay with it. Another black art.
Yes, it really is a black art. The problem is no tool really
cuts all the way to the center, as the center isn't turning.
So, it has to mash the center out of the way and/or twist it
to crumbs. The sharpness of the grinding work makes some
difference, as it makes the area that doesn't cut smaller
towards the infinitesimal. Take a look at some center-cutting
end mills with a strong magnifier, and you will probably see
differences, even from the same batch.

Jon