Hello,

I have a problem with a MCLN boring bar insert.

It works ok with a "normal" CNMG insert, but I just can't
get it to work with the Mitsubishi -FS finishing chipbreaker.
Material is just mild steel, finishing diameter about
60mm. I get totally crazy chatter - huge surface "waves"
to the turned surface (which looks really smooth except
for the large waves) - it REALLY sings. =

I've tried depth of cut 0.1 - 0.25mm, feed 0.08 - 0.22 mm/r,
and many surface speeds - less speed makes less chatter,
but not that much effect (180 - 700 RPM tried). These same
speeds/feeds/DoCs work with a normal CNMG insert, the problem
is only with the -FS insert.

What's going on? I've never experienced chatter like
this before. The boring bar is 32mm diameter!!!!!
Should have no problem with a really small chipload like this.
The tool is at center height, and I've tried lowering
and increasing height a bit, but that hasn't mattered.
The lathe weights about 2000kg and is very rigid.

Any ideas? I've not used the -FS geometry before, so there
could be some trick but it sure ain't clear to me what
it could be..

Kristian Ukkonen