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Interesting chatter case

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

Reply to
Pete Keillor
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Dull insert? Improper relief? Excess holder length?

Reply to
Larry Jaques

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"

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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.

Gunner

"The best government is a benevolent tyranny tempered by an occasional assassination." --Voltaire

Reply to
Gunner

Yeah, it certainly acted like a resonant frequency of the disk. Overhang on both tool holders was about identical, 1/2" of shank sticking out of the quick change holder. Larry might have a point, too. the first insert was a new coated carbide, probably not as sharp as the uncoated T15 from Arthur Warner.

Pete

Reply to
Pete Keillor

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.

Reply to
Larry Jaques

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