Vibration while turning bowl blank

markst · Post by **markst** » Wed Apr 20, 2011 10:58 am

I have a Mk510 machine and have recently started lathe work. While turning an 8" bowl blank I completed the rounding of the blank; it turned smoothly and there was little or no vibration in the stock as it turned. After working on it for a short while a considerable vibration set in making it impossible to work. Is this a common problem? Is there a probable explanation and a way of stopping the vibration?
Any suggestions would be welcome.
(I have used the machine for some years for other purposes without a problem)

JPG · Post by **JPG** » Wed Apr 20, 2011 11:53 am

[quote="markst"]I have a Mk510 machine and have recently started lathe work. While turning an 8" bowl blank I completed the rounding of the blank]

Has the blank shifted on/in the faceplate/chuck?

greitz · Post by **greitz** » Wed Apr 20, 2011 12:20 pm

Also make sure the set screw on the faceplate or chuck hasn't vibrated loose. If you're using a chuck, you may need to retighten the jaws as well.

Gary

ddvann79 · Post by **ddvann79** » Wed Apr 20, 2011 1:57 pm

Just a shot in the dark here, but have you checked the quill bearing(s) for slop?

pennview · Post by **pennview** » Wed Apr 20, 2011 2:05 pm

If you had turned the bowl blank round and then the vibration started, it's likely the blank has shifted position and needs repositioned as others have suggested.

If not, try removing the bowl blank and running the machine to determine if the Shopsmith itself is the problem. If the Shopsmith is OK, return the bowl blank to the Shopsmith and position the toolrest where you can eyeball the gap between the bowl blank and the toolrest as your rotate the spindle by hand -- it may help to mount a faceplate or the sanding disk on the rear spindle to enable you to smoothly turn the spindle while watching the gap. If the gap widens and narrows as you turn the spindle, the blank needs further turning until round. You can also use this technique to help recenter the blank if it has shifted because the screws loosened.

You should be turning on "SLOW" speed. If you're turning at higher speed, this will accentuate the vibration caused by the blank being out of round.

markst · Post by **markst** » Thu Apr 21, 2011 10:06 am

Thanks to all who have contributed. The obvious answer is usually correct. I had looked to see if the bowl had shifted on the chuck but although it did not look like it, clearly it had. After reading Gary's response I remounted the blank on the screw chuck, and started again, having tightened everything it was possible to tighten. Success.
Thanks again.

pennview · Post by **pennview** » Thu Apr 21, 2011 12:50 pm

An 8" bowl mounted on a screw chuck is overly large for that set-up. You really want it mounted on a four-jaw chuck or faceplate.

Here's what Shopsmith says about the screw chuck:

"D. Lathe Screw Center is ideal for small turnings --
Especially designed for turning small diameter workpieces from 1-inch to 5-inches long without using a Tailstock Center."

greitz · Post by **greitz** » Thu Apr 21, 2011 1:21 pm

He might be using the Woodworm screw attachment for a Talon chuck (or equivalent). I've had some instances where the Woodworm screw loosened in the chuck after a catch. Just retightening the chuck jaws solved the problem for me, but it's happened often enough to me now that I prefer to use a faceplate instead.

Gary

pennview · Post by **pennview** » Thu Apr 21, 2011 3:17 pm

Gary, the woodworm screw is a possibility which I hadn't thought about. But an 8" x 4" deep bowl is about max for that, at least on my Nova chuck and screw. Recommended turning speed for using the woodworm is 500 RPM on my Nova, however, and the Shopsmith doesn't go that slow unless it's the new one or you're using a speed reducer. In any event, you end up with a very thick base using the woodworm on a bowl, so I don't see why you'd use it when mounting a bowl in the 4-jaw chuck itself would be the best way to go for an 8" bowl.

greitz · Post by **greitz** » Thu Apr 21, 2011 6:47 pm

Art- Rick Davis, at one of the TA workshops, just used the Woodworm screw to initially hold the blank until you get a tenon turned to grasp with the chuck. The advantage over a faceplate is that after you turn the tenon, you just reverse the bowl in the chuck, you don't have to swap the faceplate for the chuck.

Gary