I need some Help!

[Rob Mathis]

This has been an issue for some time. I am not sure if it is me, my lathe or some of my equipment. Right now I am turning a bowl. I had it mounted to a 3 inch face plate. I worked the bottom and sides, cut a tennon then mounted my chuck. So fare everything is good. Then I flip it around and mount the chuck. Once mounted I am out of round. So I part off the face plate and use my live center and re-round the side. From there I hollow out the inside. I needed to check the depth to make sure I am deep enough, So I un-mount the chuck from the lathe, measure up everything and remount. I am back out of round now. I don't get it. What the heck am I over looking?

[Wally Dickerman]

Is your tenon too long? If it bottoms out so that the rim of the jaws doesn't make good contact, then the blank will be off line.

Wally

[Ken Fitzgerald]

Wally nailed it as I would expect from someone with his experience and talents!

You don't want the tenon to bottom out in the chuck. You want the jaws of the chuck to grasp the tenon BUT the major support is the surface where the ends of the jaws touch the bottom of the bowl....not the tenon. Thus, it's important enough that 1) the tenon is long enough...2) but not so long that it prevents the ends of the jaws to meet the bottom of the bowl where the tenon becomes one with the bottom....2. That area of the bowl immediately around the tenon should be flat to provide a good surface for the jaws to distribute the forces incurred during turning.

If the tenon is too long and bottoming out in the chuck, it can tip the bowl and make it appear to be out of round.

[Rob Mathis]

No it is only about 1/4 tall. And I had the bottom flat before I mounted the chuck.

[Ken Fitzgerald]

A couple of questions.

1. Are you turning green/wet wood.

2. Are you doing all of this in one continuous session?

[Patrick Doody]

I'm a novice so i may be totally wrong, but when i'm working on a bowl once it's on the chuck, it stays there until I'm done roughing. I check the depth, and wall thickness while the bowl is still on the lathe. I think it's tough to get it centered once you have to remount it in the chuck, at least that's what I've found. YMMV.

[Rob Mathis]

A couple of questions.

1. Are you turning green/wet wood.

2. Are you doing all of this in one continuous session?


Ken, the wood is dry, well seasoned.

Yes this is all in one session. After about 4-5 hours of work I could not take it any more so I called it a day and came here for some help.

[Steve Schlumpf]

Rob - make sure that all four jaws are touching the bottom of the bowl. Sometimes - when tightening the chuck, one of the jaws is almost touching - but not quite. Use your right hand to push the center of the bowl into the chuck while tightening with the left hand. Tighten just enough to hold the bowl - then give the bowl a spin by hand to see if it is centered. If not - slightly loosen, rotate the bowl 1/2" and re-tighten.

May take a number of tries - but it will work.

When you have time - make sure all 4 jaws of your chuck align when closed and you don't have one portion sitting higher than the others. I had to file mine down to make everything even. Just something to check on.

[Rob Mathis]

Rob - make sure that all four jaws are touching the bottom of the bowl. Sometimes - when tightening the chuck, one of the jaws is almost touching - but not quite. Use your right hand to push the center of the bowl into the chuck while tightening with the left hand. Tighten just enough to hold the bowl - then give the bowl a spin by hand to see if it is centered. If not - slightly loosen, rotate the bowl 1/2" and re-tighten.

May take a number of tries - but it will work.

When you have time - make sure all 4 jaws of your chuck align when closed and you don't have one portion sitting higher than the others. I had to file mine down to make everything even. Just something to check on.

Great ideas Steve. You know I never thought about the height of each of the jaws. As for mounted I do use my right hand and apply pressure to get it fully seated.

[Steve Schlumpf]

Rob - place something that will reflect light behind the jaws and check and see if you can see any light between one of the jaws and the edge of the bowl as you slowly rotate it. Doesn't take much of a gap to get your bowl out of center!

[Steve Campbell]

Rob. Just a thought. When you spin the chuck on the spindle make sure that it is seated good up to the flat on the spindle. It seems to me that I remember someone had a chuck that didn't tighten up tight against the flat.
Hope this helps

Steve

[John Keeton]

Though I try to never have to rechuck, I always mark my tenon and put it back in the chuck the same each time.

[Rob Mathis]

All great ideas.

I will give this a try tomorrow after work to see it this fixes my issue.

Thanks guys.

[David DeCristoforo]

I'm with JK on this one. I always mark the position of the piece in the chuck if I have to take it out for any reason. At this point I "only" have one chuck but I can see why you would want several...

[David E Keller]

You've described a pretty normal day in the shop for me. I should be taking notes on this thread.

[Rich Aldrich]

I have an SN2 and had the same problem. I had our machinist at work do a few clean up cuts, which may have helped, but wasnt the problem.

I found two issues. First issue was keep the tools sharp. Knowing the difference was an obsticle for me. Now it is obvious. The second issue was the bottom of the bowl was not flat, so the last thing I do before I flip the bowl is to take a parting tool and flatten the bottom of the bowl at the tennon.

I can still get a little run out, but most of what I turn is green wood. I believe the wet tennon does not crush evenly at the tennon when the jaws are tightened.

[Rob Mathis]

Well I tried the rotate the bowl trick and was not able to get it back to where it started out at. I could not see any gap / light at the point where the jaws meet the bowl. I did reset the chuck to the spindle too and that did not work. I tightened it to the shaft, that didn't work. Finally I gave up and pulled out the gouge and its round again.......Well until next time. While I had it all apart I did notice that there is a very slight bit of play in the jaws, when there is no pressure on them but as soon as you apply pressure the play is gone. I am only talking maybe a couple of thousands. but maybe this is enough to mess things up.

[tom martin]

Rob,
Does your chuck have an insert? If so does it have an aftermarket insert? There were several turners that bought less expensive off brand inserts that did not seat properly causing runout on the chuck. Just a thought.
Tom

[Rob Mathis]

I have a BarrAcuda that was a total kit. I bought it through PSI. There are 4 sets of jaws that came with it. Maybe it is me and not the chuck, but I would hope that I could cut the bottpm of the tennon flat.

[Steve Bistritz]

Had this problem once, the first thing I did was remove the spindle insert and cleaned it out real good and it made a big difference. Then I lined up my spindle and tailstock centers and found they did not line up perfectly anymore. Had to realign my bed by loosening the bolts and adjusting till they were good again. After that its all good again...

[Bernie Weishapl]

I had the same problem with my Rikon lathe as Steve Bistritz described. The points of my drive center and livecenter were not lined up. Every time I turned a bowl around I was out of round. Might be something to check. I would definitely check this if chuck is good. Also I never remove a bowl to measure for thickness. Never get it back quite in the same place.

[Rob Mathis]

My lathe is an Old 1947 Delta. I will check out the alignment between the centers next. Well after I finish the bowl I have chucked up.

[Jake Helmboldt]

Rob, a couple additional thoughts:

1. you may be overtightening the chuck and crushing the fibers of the tennon slightly. Heart/sap wood can be harder/softer as can some of the grain throughout the blank. Overtighten and it distorts just enough to throw things off. This is a common problem with the Oneway profiled jaws. making rechucking a pain the butt. Chuck it snug, then shug up the other side and leave it at that and see if it helps.

2. The other thing is the diameter of the tennon vs/ the jaws. If your tennon is sized very close to the jaws then you get a more complete grip around the circuference of the tennon and the jaws are less likely to dig in at only their corners and potentially distort the tennon as they grip.

Some of it is inevitable, and as John Keeton said, try to minimize the rechucking, especially once you have made a finish or near-finish cut.

[Joe Bradshaw]

Rob, I start all my bowls between centers. I shape the outside and the bottom and turn a tendon for my chuck. By doing it this way, I have a center mark on the bottom of my roughed out bowl. I chuck the bowl up and turn the inside. I usually finish the inside and then hold the bowl on a jam chuck or vacuum chuck so that I can finish the bottom. The mark from my tailstock center enables me to center the bowl for vacuum chucking.

[Reed Gray]

When you reverse after making a tenon or recess, the bowl seldom mounts perfectly true. If you have 1/16 inch of run out, that amounts to + or - 1/32 of an inch. Pretty close. The only time it really matters is if you are turning really thin, say less than 1/8 inch. If you are turning that thin, then you need to true up the outside before starting the inside.

One thing to check is if all the jaw screws are snug. Some times they can work loose, and no matter how you rotate the bowl, it never will be true.

Another thing, when making the tenon or recess, the last cut should be a VERY light finish cut, with the tool just barely touching the wood, and removing very tiny wisps of wood or dust. There is always just a tiny bit of bounce because the wood will cut differently as you go through from end grain to side grain. This will even it up a bit.

When I first started reversing bowls, I would take the chuck off the lathe, turn the bowl upside down, and then tighten it up. It helped. Now, I just free hand it on the lathe. I learned how to do it. You do have to wiggle it a bit to feel for it sitting flat on the jaws.

robo hippy

[Brian Brown]

I use a barracuda chuck also, and had the same problem. I do as John Keeton said, and carefully mark the position that the bowl came out of the jaws. Then put it back in the same way. It is not perfect, but very close. Also, don't over tighten the jaws. It is amazing how well the jaws hold with only a little pressure.

[Ron Fleice]

I do what John Keeton said
Mark the bowl and the chuck so it goes
back in exactly the same place
Ron

[Rob Mathis]

Ok I will remember to mark my bowl and try to not over tighten.

Thanks guys. Sounds like this can be a fairly common occurrence. Sounds like the key is to leave it chucked in place. And dont do as I did and remove it.

:D

[Ken Fitzgerald]

Rob,

Another thing to keep in mind........we have all probably experienced this. Don't be embarrassed to ask ANY question here. We are here to share information.

[Rob Mathis]

Thanks Ken!

Sometimes it is so easy just to ask for help.

I have no problem asking the brain trust.

:D

[Rich Aldrich]

Rob, this is a really good post.

Jake, I think you hit my problem. I tighten the crap out of my chuck on the tennon, the fibers are crushed unevenly. I will try the light touch next time and keep an eye on the tightness.

[Reed Gray]

When you mount the bowl, don't put it in so that 2 jaws are on the end grain, and 2 on the side grain. Rotate it about 45 degrees either way. This way the 4 jaws are on pretty much the same grain orientation. On small bowls it doesn't make much difference. On larger green bowls, it can make a lot of difference. On dry wood it doesn't make much difference, on green wood it makes a difference. Also, when tightening, if you have a keyed chuck, tighten in one hole, then rotate and tighten in the next. Some times I will go around a couple of times on larger pieces. You really don't need to armstrong it, just get it nice and snug.

robo hippy

[Rob Mathis]

The grain orientation is a good point. And I have never gave it a thought when I chuck up a bowl but I will be thinking about it a lot more in the future.