On Sat, 20 Oct 2012 03:30:31 -0700, Gunner
wrote:

On Fri, 19 Oct 2012 15:22:18 -0500, Pete Keillor
wrote:

I spent a while this afternoon turning a rough sawn aluminum disc for
a reel flange to 6" diameter. Earlier I put it on the aluminum reel
center with a shrink fit. I was taking small cuts to avoid
overloading the shrink fit, and at first didn't notice the high pitch
ringing due to the intermittent nature of the cut. Once I got a
continuous cut, there was a light high pitched squeal, and I could see
fine grained chatter marks in the finish. As I approached final
dimension, I tried varying the speed all over the place, including
back gear, and feed amount within a fairly small window, and the pitch
of the squeal never changed.

I finally changed the insert from a sharp radius carbide back to a
1/32 radius T15. Instant joy. The squeal was gone along with the
chatter. Anybody have an opinion on the cause of the chatter? The
carbide insert had about a 1/64 radius and I was using a left hand
bit, feeding left. When I switched, it was a right handed bit, still
feeding left.

Pete Keillor

Sometimes...it just happens. The sharp point on your original insert
started to produce a vibration that had multiple harmonics that were
not dampened by your tool holder etc

Try shorting the tool holder stick out..sometimes even a 1/8" will do
the job. Other times...not

You put more bit on the cut..which dampened out the harmonic and it
worked.

This is the reason I use KDK tooling, because they are massive..and I
keep my tools as short as possible. And sometimes I still have a
harmonic issue that requires addressing in a bunch of different ways.

As I do CNC lathe repair..Ive seen this MANY times on clients machines
and have helped them resolve the issues.

I got called into a shop once..a 2 hour drive each way..because they
were sure they had bad spindle bearings or ballscrews. It was a
harmonic from a 5/8 round tool on a tool bar in a "magic sweet spot"

http://www.omniturn.com/images/805-pfb_combined-s.jpg

We moved the tool holder about .250 in one direction and pulled the
tool in .500...and voila!! No more problems.

This after an hour of checking the machine from top to bottom and not
finding a damned thing wrong with it.

That's an ideal situation for a businessman. You got paid to learn
something new (or relearn something you already knew) and got another
way to repair machines under your belt. That can result in client
retention and/or new clients in the future. Win/win.

--
Fear not those who argue but those who dodge.
-- Marie Ebner von Eschenbach