I assume you mean a slow feed rate, but not a slow cutter rotational
rate--- My amatuer calculations say that end mill should be run at
3200 rpm if stock is mild steel and mill is HSS. I read somewhere that
the main cause of small drill bit breakage is running them too slow. I
suppose the same thing would go for your end mill.

As far as hardness of your material goes, simply use a good file and
compare the unknown material's "fileability" with known hard or soft
stuff. If your mystery metal is a lot harder to cut than some mild
steel, toss it and get some known material.

But:

I would simply make the part from 3 pieces and bolt them together. The
center piece would be the 1/8" thick material that would space out the
outer sides.
Hope this makes sense,
Pete Stanaitis
--------------------------

gtslabs wrote:

I set my bridgeport up to cut a thin slot in a piece of steel. So far I
have only broken bits.
I dont know much about hardness but the material I am using has a black
coating. Not sure what that is. But I started off with a 1/8" endmill
taking very light cut at a very slow speed. I am having no luck.
Additionally, I need my slot to be deeper than the endmill itself.

What I am doing is setting up a 2 brackets to hold a 1/8" x 1.25" x 12"
long cutting bar. I am sure there has to be an easier way but it might
take more pieces than cutting from one.

Any suggestions?
Thanks