>I've got a walnut bowl blank that a turning friend gave me to help me get started in learning to turn bowls. He roughed it June '02 and let it air dry. It has warped somewhat, but not too badly. The walls are about 1/2" thick. If I put the bowl on a table upside down, it would wobble. The base of the bowl has a tenon which is too big for my talon chuck. The bottom of the tenon shows a small crack, so that has to go in favor of a recess or a shorter tenon - depends how it goes. My problem is mounting it up to finish it off.
To do battle with this, I have a talon chuck, a faceplate, and the centers that came with the lathe.
I think the plan has to be to mount the rim of the bowl to a faceplate, as best I can, and true up the exterior, removing the tenon in favor of a recess (or a shorter tenon to defeat the crack), removing minimum wood from the exterior. Then I would mount the base to the talon, and have at that interior. My greatest concern is having a consistent wall thickness, especially at the rim. I'm not sure I can avoid some variation there, between the warpage, my mounting method, and the tendency of the wood to distort while spinning, other than to use low speeds. I just don't want to end up with a bowl that has a 3/8" inch wall thickness on one side, and 1/8" on the other.
Hopefully you have enough material to get a finished bowl out of. 1/2" sounds a little light depending on the diameter of the bowl and how much it has warped. Assuming it hasn't gone out of proportion, you'll want to jamb chuck the bowl with the tenon towards the tailstock and re-true the tenon. A jamb chuck is just a piece of wood or something held by your chuck that is jambed into the bottom of your bowl. This will drive the bowl.
Once your tennon is round, rechuck the bowl and return the outside of the bowl, the return the inside of the bowl, then you can use the jamb chuck again to remove the tenon completely.
I might suggest getting Bill Grumbine's video since he does this exact procedure and explains it in detail. Excellent source of other useful information such as getting a bowl to the point yours is now and what to do once you've turned the tenon off. Good luck.
I'd first measure the long and short dimensions across the top of the bowl to be sure you have enough wood to work with to get a round bowl again. If so, here's what I do:
1. Mount the bowl between centers, with the foot toward the tailstock. I drive the open end of the bowl with rounds of scrap wood that I've turned to fit my chuck, or you could use a piece of scrap Pine/Poplar screwed to your face plate, turned to a disk a little smaller than the inside top of the bowl. It will only touch in two places inside the bowl if the bowl is oval, but that will be fine with tailstock support. It helps a lot in centering the tail center if there is a little dimple in the middle of the foot from the first turning. Or, you can move it to and fro to center it the best you can. I also find that revolving centers with interchangeable tips are very helpful here, as a conical point will want to keep heading into the same hole, so I use a tip with a circular ring tip.
2. True up the tenon, shaping it for your partuicular chuck & jaws, and if there is enough wood there, you can make it shorter. I always remove the tenon, and shape a proper foot as the last turning step, so I'd glue the crack you have and leave it alone for now -- removing it later, unless the crack looks like it will result in the tenon being torn off the bowl. I generally don't use a recess, as that usually ends up resulting in a larger foot than I want, and in this case I don't recommend it, especially if you're working against a crack that could split the base of the bowl.
3. Carefully true up the outside of the bowl between centers, from foot to rim, removing as little wood as possible. Many people sand and finish the outside here, but I usually sand now and seal/finish/polish last.
4. Mount the bowl on your chuck, and very gently true and shape the top surface, and the inside of the bowl. You may get significant vibration, as there is less support than before. You can reduce this by supporting the outside of the bowl with a few fingers or a bowl steady, using a slower speed, and taking very light cuts with a very sharp tool.
5. Sand and finish the inside.
6. Re-mount between centers, as before, with a few layers of paper towel or a layer of cloth between the wooden disk and the sanded/finished inner bowl surface to prevent marring. I usually shape the wooden disk to have a gentle curve close to that of the inside of the bowl.
7. Now I sand and finish the outside, then shape a foot, very carefully removing as much of the tenon as I dare, leaving a little nub that is carved off by hand, and sanded off-lathe. How much of a nub you leave will depend on your experience, how daring you are, the soundness of the wood, and the size and weight of the bowl -- a bigger nub to support a larger bowl. I usually get down to about 1/4" to 1/8", and with smaller bowls, I can sever the nub completely with a long bevel spindle gouge, holding the bowl up against the headstock with a little extra pressure from the bevel, and switching the lathe off as the cut is completed (still holding the bowl in place with the back of the gouge). If you look in the tool grinds library, there's a convex bevel spindle gouge shown by David Ellsworth that would be good for this step.
Note: For steps 6 & 7, many people use Cole jaws, or Bowl jaws, or Jumbo jaws, as different manufacturers call them, to hold the bowl by its rim, or carefully turn a jam chuck from scrap that has either a recess just big enough to jam the bowl into, or a tenon just small enough to jam the bowl onto -- these hold the bowl by friction when shaping the foot and removing the tenon.
Others may do it differently, but this works for me.
>Thanks for these great replies! I never really understood a jamb chuck before, now I get it, and really appreciate the help.
I must say, the step of turning off the tenon with your right hand, while holding the bowl in place with your left hand kind of, and turning off the lathe with your third hand at the exact moment.....well, I'll try not to get emotionally attached to the bowl before I try that one. I've got color pictures in my head on how that could turn out. "No, that red smear on the bowl isn't stain. That would be DNA."
Also - I just bought five old salad bowls at a rummage sale for $1, that have recesses/tenons on the bottom. I think they'll be good practice for me to play with. They are marked on the bottom, and are all slightly different, so I'm picking up somebody's old turning project. I think the previous turner used corn oil on them, as they are pretty sticky.
No one says you have to turn the tenon down to nothing and catch it at the last minute while it's still spinning. It's not cheating to turn the lathe off after you've parted the tenon down to 1/4 inch and use a finishing saw to finish the cut. It just means more elbow grease needs to be applied at the sanding phase.
At the beginning of your turning career, safety and paying attention should be your main concern. Tool control, form, cut, sharpening, and all the rest doesn't mean anything if you can't stay out of the hospital. Don't do anything (except wearing face, eye, and head protection) that doesn't feel comfortable and puts you off balance in front of the lathe. As you get better, you'll figure out where you feel more comfortable with a technique and modify it to fit your needs.
>Thanks for the safety follow up. This is one of those moves where I'll think for a while about how I would execute the move, and then determine whether or not I'm comfortable in doing it.
A few years ago I might have been more cavalier about it, but now I've got a wife, a youngster, and one that hasn't come off the lathe yet who might actually give a hoot if I got toppled in the shop. How's this for a safety tip - keep some family pictures in the shop.
>To add to what Brad just posted if you have a situation where the tenon can't be saved you may be able to use a waste block. Center the bowl up like Brad outlined then turn the tenon down to about 1/2 of an inch. Get the bottom of the bowl up to the tenon as flat as you can. Remove the bowl from the lathe. Chuck up a waste block in you chuck or face plate. Drill a 1/2" matching hole into the waste block to fit the stub tenon that is left on the bowl. Glue the bowl to the waste block and use the tail stock to provide clamping pressure. Personally I use tightbond and let it sit over night. I do almost all of my bowls this way, the advantage is that you can completely finish the outside of the bowl in one step (except for the bottom of the foot).
Wow -- I never meant for you to do anything life threatening ! I'm sure it all sounds more complicated than it is in real life. If you are just starting out with bowl turning, Raymond's advice is very sound -- safety first, and technique comes with practice.
I always remove the nub by hand unless the bowl is small and relatively light. With a close fitting jam chuck you can turn the remains of the tenon away safely, but I still do as much as I can with tailstock support, and then very gently turn away the rest. The wood isn't moving very much at the center of the foot (on axis of rotation), so there is a tendency to knock bowls out of their fixings by trying to take too heavy a cut near the center of the foot. This can happen with Cole jaws, or bowl jaws, too.
After a while, in some situations you will feel comfortable supporting the bowl lightly with one hand, while controling the gouge with the other. I do this all the time when finish turning the rims and upper portions of thin bowls while they are held by a tenon in the chuck. In practice, a few fingers support the spinning bowl, while the thumb and maybe the index finger support the gouge on the rest, working in tandem with the right hand holding the gouge -- easier to show than explain. This is sometimes very useful for reducing vibration on thinner pieces -- it does take practice, though, and should nEVER be done if there are cracks near the rim, or if you haven't developed the necessary tool control -- you need to KNOW that you are not going to "have a catch", as they say in Field of Dreams.
If you are driving a bowl from its open end with a disk of wood, a shaped piece of stiff foam, or a jam chuck, its a simple matter to gently hold the bowl in place with one hand (my left hand, usually) while the lathe is spinning slowly, and while rubbing the bevel of a spindle gouge against the bottom of the almost completed foot, turn away the last of the tailstock support. This isn't a life-threatening white knuckle ride, really. If you are rubbing the back of a turning tool against the foot, pushing the bowl toward the headstock, while holding the bowl with the left hand, you can let the left hand go, and hold the bowl there with just the gouge. You may not be ready for this now, (and might never need to do this!), but store it away in the back of your turning mind, and it will be there if you need it later.
Brad - I wasn't really serious about being concerned over life and limb with this, though it is pretty clear you need to be a bit careful with that move. Sorry I wrote it up that way and gave you concern. I've parted off a couple of things like that, and based on my limited experience, I'm actually more concerned that the bowl will go "dink....dink....dink...rollllllll...CRACK" across the concrete floor. Not that I've ever done that.
