Wobble

[Mike Minto]

I have a problem which comes up far too often. When making a bowl, or especially a hollow form, sometimes they come loose and fly off the lathe wether from a glue block coming loose, wood tearing, remounting a previously rough turned green piece, or whatever reason. Anyway, when I try to remount the turning, it is always off center to some extent due to my gluing on a new block a little off center. When this happens to you other guys, do you hope you just have enough wood to turn the item smooth again, or have you got a special way of re-centering that I'm unware of? Thanks, Mike

[Jim Underwood]

Mike,
If you can see a way to assist centering the bowl or hollow form with a large cone on the tailstock or headstock fitted into the mouth or top then do that.

I know lots of turners when turning a bowl will turn first between centers to get the thing round, then turn a tenon on one end. They'll rough turn the piece, leaving the tailstock center mark on. Later on when the piece has dried, they'll recenter the piece using the old center mark, and re-true the tenon, then use that in the chuck.

Other than that, all I know is to use the centers and adjust as necessary until your piece has little or no runout. (Don't ask me how well that's worked out for ME.;) )

[David Walser]

Mike,

Remounting a piece presents a number of challenges. In general, try the following:


Turn the remounted piece by hand and use a pencil to mark the "high spot". That is, hold a pencil against the piece (support the pencil with the tool rest) and spin the piece on the lathe. If the piece is not perfectly centered, the pencil will leave a partial line going around the piece. The line represents the "high spot" and the "no line" is the low spot.
Recenter the piece.




If you are using a chuck: Recenter the piece by slightly loosening the chuck and "tapping" the high spot of the piece with the palm of your hand or something else that's, er, handy. Tighten the chuck and repeat step 1 to see if the piece is centered properly. Repeat steps 1 and 2 until you're satisfied.
If the piece is between centers: Recenter the piece by loosening the tail stock and moving the high side of the piece "down" closer to the drive center and/or the tail stock's live center. You want the point of the center to go into new wood. Repeat steps 1 and 2 until you are satisfied.
If you are using a faceplate: Recenter the piece by removing it from the lathe and carefully moving the face plate "up" towards the high side of the piece. Tapping the piece, like you would with a chuck, is not recommended. You'll either tear the wood around the screws holding the faceplate (allowing the piece to wobble as it spins on the lathe) or you'll weaken the joint of your glue block (with potentially disastrous consequences).

These same principals apply when you are reverse chucking a bowl to turn it's foot.

Sometimes, of course, it's not possible to get a piece to run perfectly true because the wood has moved such that it's no longer round.

Good luck.

[Kim Ford]

Mike,

I fought with this problem for a long time. The solution for me came down to a couple of things.

I bought a used independent 4 jaw chuck along with a cheap dial indicator ($20 online) and now if I must find exact center I can. However, the best course of action for me is to never loose center. I do that by not using my scroll chuck for anything but rough work. When I am ready to finish the piece I glue on a sacrifical block and then leave it on until I finish the foot with the vacuum chuck.

If you loose the block and must put another one on, then find exact center with the 4 jaw and center the new block to be glued on with a wood cone from your tail stock live center. Please understand I use the term exact center knowing that exact has different meanings to different turners.
Note: Independent four jaw chucks can bend thin wood. If the wood is thin then only use the chuck to find exact center and align the new block.

In my opinion using sacrifical blocks necessiates a vacuum chuck. Last year I built a vacuum chuck from the plans Steve Schlumpf posted here on the creek, (Thanks Steve the best money spent in my shop) WOW!! Now I would not be without one.

[Richard Madison]

Mike,
Some good advice on re-centering. But seems like you would also want to address the real problem(s) of what is causing stuff to unintentionally part company with the lathe. That really should not happen except in the event of a fairly serious catch.

[Robert F Walker III]

Actually It may not need a catch to break it off make sure the glue you are using is fresh and its appropriate to the application for example I do not use a polyurethane glue for a block while very strong laterally it has very little sheer strength. I have had block let loose just turning on the lathe no tool every touched it. and If I use a cryonate it better be fresh especially on anything other than small peices I usually use A titebond type glue. I got tired of having them let go. Part of it might be here in florida its hot and stuff just breakes down quickly when at 90 degrees constantly that a lot of guys farther north dont experience .
Just my two cents