Wobble

[Randy Hogan]

I've turned about 25 bowls in my newfound wood turning hobby. I typically use a faceplate, sometimes a screw chuck to mount the blank and turn the outside. I tend to choose a recess over a tenon and I create the mark for it with calipers. Lining up both ends of it to find the center. Seems like a routine kind of thing, but when I mount the recess on the chuck to turn the inside, I have been getting a wobble in the blank right from the get go. And it's happens on a fairly consistent basis. My lathe is a new G0766 and my chuck is a new HTC125. So I'm pretty sure I can rule out a lathe or chuck hardware problem. So I presume its my inability to create a true recess as the problem. I'd appreciate any insight.

[Peter Blair]

I doubt it is your ability to create the recess though I seldom use this method. Don't forget you are dealing with wood which is often softer in some areas than in other areas and thus the jaws may grip differently and cause a minor wobble. The I reverse a pice I often get wobble and always leave the final outer shape finishing until the piece has been reversed. Another cause could be the chuck most are not milled 100% accurately you could check this with a dial indicator and often the jaws act a little differently when moved from place to place on the chuck.

[JohnC Lucas]

Quite probably the shape of the recess and maybe how your are mounting the wood. If I'm correct the HTC125 is a copy of the Vicmarc chuck with dovetail jaws. The shape of the recess should be such that the jaws hit the bottom of the bowl and the side of the recess. Ideally they should not touch or barely touch the bottom V of the recess. In other words your V recess should be exactly the same or slightly narrower than your jaws V. This will allow it to register against the bottom and sides and will sit more accurately. The other thing is to mount the bowl so that each jaw has an equal amount of side grain and end grain. If you draw a line parallel to the grain and then another perpendicular to the grain you will have an X. If you align this X so it's on the opening between each jaw you will have an equal amount of side grain and end grain being compressed by the jaws and it will usually help alignment. That being said wood is a fickle thing and you can't assume that all parts will compress the same. so even if you take the utmost precautions you still may get some wobble.

[Randy Hogan]

Ok guys, thanks for the input. My chuck does look suspect when I turn it at 60rpm. Not running true watching it w the naked eye. I am pretty meticulous on the shape and size of my recess. But I will heed your advice. I have learned over the years that professionals to the basics well, along with doing many, many little things correctly. So I have picked up some tips today. Thanks again.

[Reed Gray]

Well, how much wobble are you getting? When reversing, there is always a bit of wobble, both with tenon and recess. If you have 1/16 inch run out, that is fairly good if you consider that is 1/32 +/- ... I do prefer a shear scrape cut for the final pass on the inside of my recess. When you rub the bevel, this always adds a tiny bit of bounce. NRS (negative rake scraper) will do pretty much the same thing, though not always as clean of a cut. I have had times when there was more run out than I considered acceptable. I did figure out eventually that some times this is due to one chuck jaw getting a bit loose (set screw). Some times just rotating the bowl 90, or 180 degrees can help too.

robo hippy

[Dwight Rutherford]

Does your chuck have an adapter? Is it seated into the chuck? Is the set screw tight?

[Don Jarvie]

Try this. Mount the bowl on the chuck and tighten it enough to hold it in place. Pull the tail stock in place so it’s in the center hole and allow the bowl to to move back and forth slightly. Pull the bowl toward the tail stock so the bottom of the recess is off the bottom of the bowl but still has enough wood for the chuck to grip and tighten the chuck.

There will still be a little wobble but the tail stock will help center the bowl on the chuck.

[robert baccus]

Why reverse the piece--turn inside and outside from the one recess hold. Or double turn like green wood--turn the outside leaving 1/4" of wood and return all of it after reversing it. If you must drill your recess after cutting the outside mark the center and some circles on the bottom while still chucked up for the initial cutting and toss the dividers.

[Thomas Canfield]

Quite probably the shape of the recess and maybe how your are mounting the wood. If I'm correct the HTC125 is a copy of the Vicmarc chuck with dovetail jaws. The shape of the recess should be such that the jaws hit the bottom of the bowl and the side of the recess. Ideally they should not touch or barely touch the bottom V of the recess. In other words your V recess should be exactly the same or slightly narrower than your jaws V. This will allow it to register against the bottom and sides and will sit more accurately.

I may be reading this wrong, but often the recess is not as deep as the jaws of the chuck and the jaws should seat firmly then against the bottom of the recess and against the sharp vee of the recess for dovetail or sharp 90 degree for straight jaws. Sounds like seating issue as first thing to check.

[John K Jordan]

I may be reading this wrong, but often the recess is not as deep as the jaws of the chuck and the jaws should seat firmly then against the bottom of the recess and against the sharp vee of the recess for dovetail or sharp 90 degree for straight jaws. Sounds like seating issue as first thing to check.

I think it was Mark Gardner who pointed out a source of error when mounting in a recess is a dovetail vee that is not cut perfectly clean. He suggested instead of making a flat recess bottom, slope the bottom of the recess slightly near the dovetail such that the inside circumference of the chuck jaws press against the wood in the bottom of the recess instead of the flat of the jaw tops pressing flat against the wood. This will keep the tip of the dovetail a tiny bit out of the vee and avoid any imperfections there. (No problem, of course, if the dovetailed recess is cut perfectly clean.) There is no compromise on strength of the hold. I've been doing this lately and it appears to work fine. This would be a lot easier to understand with a drawing...

Also, I remember Chris Ramsey being fastidious about mounting the chuck to the lathe and the wood to the chuck, making sure there was not one stray fiber or even a bit of sawdust on the jaws, lathe spindle, or on the tenon. I've been more careful about this since and things appear to run truer now.

Another thing - chuck jaws are sometimes not completely concentric when mounted on the chuck. I use a Glaser screw chuck to turn the bottom, then before reversing I cut a concentric recess to hold in a scroll chuck. Any runout in the jaws can cause a big problem. If I measure any runout on the outside, I dress the jaws with a file or sharp scraper while spinning on the lathe. I first minimize the play in the jaw slides by tightening the jaws on some thin strips of wood, ideally the width of the saw blade used to cut the jaws apart when manufactured.

JKJ

[Reed Gray]

Maybe this will help:

https://www.youtube.com/watch?v=5KHkkws9lWA

robo hippy

[Randy Hogan]

Yep, thanks guys. Might be a combination of small errors that give me the problem. I did reverse one on a tenon and I had no trouble with it. I appreciate the responses!

[bobby stout]

I have the same set up as you and had some wobble. I bought a few machined washers or shims of different thickness and put them between the chuck and lathe and fixed the wobble in the chuck. You could see mine wobble this took it all out. But I d as others I finished the outside after I have reversed the bowl.

[Randy Hogan]

I have the same set up as you and had some wobble. I bought a few machined washers or shims of different thickness and put them between the chuck and lathe and fixed the wobble in the chuck. You could see mine wobble this took it all out. But I d as others I finished the outside after I have reversed the bowl.

I swept the shavings for the first time in awhile from around the base of the lathe. I noticed the whole thing had 'walked' several inches to the left. I've had, what appeared to be 'whole machine vibration' at the headstock end when I'm taking a big bite with a gouge at a fairly fast feed rate. I've checked and leveled the legs a couple times. It appears that the ballast weight of the machine is not substantial enough for the size of work I'm turning. I'm sure all of this isn't helping my wobble problem, although I have done some work recently without much run out at all. I think my next step is to put in some anchors in my concrete floor and anchor strap the head stock end down as tight as I can get it and see if this eliminates the vibration. When I first installed the lathe I had no vibration whatsoever so something obviously has changed. In addition, with a 22" swing, it doesn't appear the overall mass of the G0766 is heavy enough to handle it. The largest bowl I've turned is 16". But then again I'm new and I might be all wet.

[Michael Mills]

Before you tie it down you may want to try this... see video from Lyle Jamieson.
It removed about 60% of the vibration with my Nova 1624 and you have a 300 pound advantage
His description is not as detailed as his full video so...
Unless all four feet are planted the same it can teeter on two of the diagional legs (like a see saw).
Chuck up an out of balance piece.
You can use any leg but maybe for safety and convenience the R front.
With the lathe running adjust the foot up or down. You will be able to see and feel the change in shaking/vibration.
Not all will be removed but a lot can be removed.
Note: if you go too far then it will start teetering on the other set of diagional legs.
www.youtube.com/watch?v=AWYEPfqRet8