Hi, I'm currently making a thick flange on a CNC mill. The material is
a 1/2" thick plate of 321 stainless. Previously, we made a prototype
out of 3/8" mild steel. That piece cut relatively easy, as was
expected. We knew that the thicker stainless piece was going to be
much tougher to cut, so we made sure that we used lower speeds and
plenty of coolant.

Here's the problem: Starting with a new Sossner 4 flute high speed
steel endmill, the same kind that we used to cut the prototype, we
began cutting the 321 stainless. The first 1/8 inch or so it was slow
but steady, we expected it to be tough. But after that it began to
chatter and the cutting slowed down. By about 1 inch of cutting, the
endmill was worn out.

Something's not right here. I knew it would be tough but not THAT
tough. How come the endmill wore out so quickly? I know that people
who work with stainless don't go through 30 endmills to make a
relatively small piece.

Does anyone have any recommendations of what kind of endmill to use to
cut thick 321 stainless? Is the material that our endmill is composed
of simply too soft a metal? Replacing cutters every couple of inches
isn't an option.

I'm sure that someone can lead me in the right direction.


Thanks,

Marshall