Lathe Harmonic

[Luke Maddux]

I've just gotten a new lathe. A big powerful one with EVS. I'm turning a 12.5" bowl right now and when I get it to a certain RPM it vibrates a little. Not enough to move the lathe, but enough to notice it. See my previous post for more details. There is some important information in the post.

I realized today that if I turn the RPMs up, oddly enough, it goes away!

I'm obviously not dealing with some kind of linear relationship between RPM and lathe balance. If that were the case, faster would equal a more violent vibration. Something strange is happening. I believe that something is referred to as a Harmonic. Basically, with a blank THAT diameter spinning at THAT rate and weighing THAT much, the lathe just wants to vibrate for some reason.

Has anyone experienced that before? Actually being able to eliminate vibration by increasing RPM?

Very interested in responses.

Cheers,
Luke

[issatree]

Hi Luke,
You have hit the nail on the head.
Been saying that for a long time now, but mainly been told I'm wrong.
Well that's their headache.
Out of interest, which Lathe did you buy.

[chuck1]

Yep same here and when turning spindles poping the speed up will can stop the Timber running out but use some caution.

[keltrader]

Harmonic balance. Same principle used to match shafts in a set of golf clubs or increasing your speed when driving over a corrugated road.


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[Luke Maddux]

Cheers, guys.

The lathe is a Jet 1642 EVS. The 2hp model.

So given that we are in agreement on what is going on, is there anything I can do to resolve the issue? I've only had two short sessions on this particular bowl but will finish it this afternoon. My hope is that as the mass decreases (I hollow the bowl) it will be reduced to an eventual nil.

[chuck1]

Bolting the the lathe down, adding more weight to the lathe e.g sand bags.

[Paul39]

Luke, Below is one of my typical bowl blanks. I had just gotten the Woodfast home and had to try it out. Outside on dirt with the out of balance blank, the lathe and stand just rocked back and forth at a very low speed. In addition to the step pulleys I have variable speed. As it got more round, I ran it faster.

It may be that you are not used to the normal movements and vibrations of wood turning.

You might have an experienced bowl turner come and have a play with your lathe to see if anything is out of the ordinary.

The Woodfast now sits on two 150 X 150 mm pieces of timber on a dirt floor. It is not screwed down and I have no trouble with rough cut 500mm out of balance blanks.