On Sun, 31 Oct 2010 16:58:48 -0700, mkoblic wrote:

I am sorry to ask something very basic. My excuse is that I am testing
the Forte Agent :-)

I need to make round holes in steel, 1/8" deep, with flat bottoms. The
diameter is usually either 1/4" , 5/16", 3/8" or 1/2" and is not
critical.

I do these on my mini-mill. I pre-drill the hole to the required depth
undersize and then use a 4-flute mill to square up the profile.

All is well until I start getting near the bottom. The machine begins
to labour and there is a tendency for the table and/or the head to
want to move in a circular fashion, clamping x and y notwithstanding.
I assume that this is due to the mill beginning to remove more
material, particularly the center portion of the hole.

The end-mills are supposed to be centre-cutting. There are two flutes
that meet in the middle, the orthogonal two flutes do not. All the
pictures I could find suggest that these are indeed centre-cutting
end-mills.

So the question is: Is this a normal behaviour for end-mills in this
situation? If not, what is the likely cause? Is there a better
procedure to do this?

Are you going full depth in one peck?

Thanks,
Rich