On Fri, 13 Feb 2015 01:36:10 -0800 (PST), robobass
wrote:

I'm new to high speed machining. I'm cutting a brass part
http://i1262.photobucket.com/albums/...63/Chatter.jpg
with a 4mm HSS Co TICN cutter. The surfacing works fine, but when I try to make a deep counterbore I get a really bad finish. I'm running the tool at 10k rpm (spindle range is 8k-25k rpm) and the finishing pass at F300. I'm not sure what my F values actually mean, like in ipm, but it looks like a good speed. I suppose my my options are to use a carbide cutter, go to 6mm diameter (max on this spindle), or adjust the feedrate and spindle speed. Can anyone take a look and make suggestions? I know I should get myself a proper knee mill, but that's not a realistic option for me at the moment. I'm hoping the machine I have
http://i1262.photobucket.com/albums/...r1963/CNC1.jpg
will be adequate if I tweak the operation enough.

Brass likes to grab cutters -- they dig in if they have any positive
rake at all. Zero rake or slight negative rake may solve your problem.
On a lathe tool, that's easy. On a milling cutter, your options are
limited. You can try dubbing off the very edges of the cutter with a
small stone.

First try just giving it a little radius -- really small. If that
doesn't do it, try honing a slight negative angle on the very edge. At
those rpm, you don't have to hone more than a couple of thousanths
back from the edge, because you aren't cutting deep to begin with.

Your machine and the coarseness of the chatter suggests, however, that
any "digging in" is being amplified by a lack of rigidity in the whole
setup. That's going to make it tricky.

Anyway, this is a cheap and easy thing to try first.

Cute kid, BTW.

--
Ed Huntress