Re: end mill types

Ian Wright wrote:

> HI,
>
> Can you elabotate on the 'corner cutting end mills' please? As far as
> I was
> aware, any endmill has to produce rounded inside corners simply
> because of
> its own mass - is there something I don't know?

All end mills must cut rounded corners when you look down the axis of
the
cutter (at the X-Y plane). But, a square-end end mill (slot drill in
UK) will cut
a square corner as seen from one of the orthogonal planes. In other
words,
the sides of the pocket must be rounded, but the intersection of the
side and
the bottom can be a sharp inside corner. This could cause stress
concentration
and fracture in pieces that are under stress, thermal cycling or
fatigue.
A radiused end mill has a rounded edge, you could think of it as being
halfway
between a square-end and a ball-end mill. These are often avaliable
cheap
from the regrinders as they can quickly regrind square-end mills with
chipped
points to a radius. These are desirable for easily making parts with
built in
stress relief, and the radiused edge of the cutter is more resistant to
chipping
than the sharp point.

> Also, I believe that the 'end cutting endmills' you are referring to
> are
> generally known as 'slot drills'

Most technically, only two-flute end mills are called slot drills. And,
I NEVER
mill a slot to the tool's diameter in one pass, because the edges are
ragged
due to tool deflection. I always use an undersized end mill and then
make a finish
pass down both sides of the slot.

Jon