GeoLane at PTD dot NET wrote:
A continuation of my query regarding slot milling with a 1/8" end
mill.

The peripheral feed per tooth recommended was 0.0005" for a 1/8" end
mill.

What's the feed per tooth for 3/16 to 1/2" end mills? Is there any
rule of thumb?

The info on my McDonnell Douglas speed & feed calculator (slide
rule sort of thing) says for end mills under 1", multiply chip
load value by cutter dia. So, for aluminum, they recommend
..010" feed per tooth at 1", so for a .125" diameter cutter, that
should be .00125 (I'd be conservative, especially with HSS, you
can watch the cutter bend under load.) So, 1/2" should be real
safe at .005" feed per tooth.
Second question. With a center cutting end mill, what's the down feed
rate? BTW, I've got to do this by raising my table - my old BP head
has no downfeed.
I use something like 1/4 to one half of the feed rate you'd use
for side cutting. When this is a straight plunge into solid
material, there's no side force, but the chips tend to pile up.
It may be better to make short stabs at it and then come up to
clear the chips and apply coolant. Especially with aluminum,
heating of the workpiece softens the aluminum, and then it
sticks to the cutter, and you have a mess. So, you may have to
allow cooling between cuts, use plenty of coolant, or other
strategy. With a little experience you learn the kind of things
that lead to the heat buildup. In some cases racing along with
several cuts much shallower than rigidity dictates helps to keep
the heat buildup from causing those messes. Also, knowing the
alloys is important. 2024-T6 and 6061-T6 cuts like a dream, and
you have to work at it to run into these troubles, like using a
dull tool. But, 2024-T1 will drive you nuts, it is so soft it
tears rather than cuts cleanly, and then the tool gets hot.


Jon