big bowl

[jeff oldham]

well I glue up 3 pieces of wood,,2 of them was cherry and the other maple I believe,,i used a screw mounted in my chuck to get it round,,i every tenon I put on the bottom broke loose,,i put 2 inside tenons and 1 outside tenons and had different depths on each one,,all broke loose,,can anyone tell me what I am doing wrong,,

[John K Jordan]

...every tenon I put on the bottom broke loose

Some questions to minimize guessing:

How big is the bowl and what was the diameter and depth of the bottom tenon?

Did the wood break or did the tenon pull out of the chuck?

What kind of jaw set is in the chuck and was the tenon cut to fit that type of jaw?

Did the tenon break when you had a catch with the tool? What tool were you using?

Were you roughing an out-of-balance blank or was it already turned round and balanced?

If it was an unbalanced blank, were you turning at a slow speed?

[Reed Gray]

A 12 inch bowl should have a minimum 3 inch diameter tenon, and 4 is better, just to give a size reference. Mike Mahoney says that the tenon should be almost half the diameter. One that size can take a lot of abuse. I have a clip up on You Tube on mounting bowls on the lathe. That might help. Just type in robo hippy

robo hippy

[David Delo]

Jeff, I saw a picture of the "bowl" you put on LJ. Kind of hard to tell dimensions from a picture but it looks to me as if your piece is at least 6 or 7 inches thick and you were hollowing it out and you were maybe 3 or 4 inches deep when it broke off. That's a lot of distance from the toolrest to use a bowl gouge. Since your in Greensboro, I'd suggest you go to the Piedmont Triad chapter meeting next Tuesday and get some help. 5:30 p.m. at the Leonard Rec Center on Ballinger Road. Good luck.

[Thom Sturgill]

Using Novas jaw chart since they publish this and I do not know what chuck you are using --

The 100mm Jaw set is good for 14 11/16" x 5" in a recess and 12" x 4" or 6" x 5" using a spigot.
The 130mm Jumbo Jaw set is good for 29 1/2" x 3" platters with a recess or spigot
The Power Grip Jaws are good for 16" x 6" with a recess and 8" x 12" with a spigot.

Note that a spigot gets greater extension from the chuck, not greater diameter - the 100mm jaws extending from 4" to 5" from the chuck reduces the working diameter from 12" to 6".

While turners use these in larger blanks than this all of the time, (and turn faster than the rpm limits), if you are exceeding these by too much you should maybe try using a faceplate or a faceplate on a glue block.

[Olaf Vogel]

every tenon I put on the bottom broke loose



Not sure what you mean by "broke loose".
- the wood broke, or
- the tenon came loose from the wood?

I've done a lot of large pieces that hugely exceed the guidance parameters above and not had anything come loose
Not recommending that. Just suggesting that the size of the jaws/chuck is less likely the issue, more likely how you use the tools.

Suggestions
- make a tenon that narrows from the base.
- ensure the tenon is the right diameter to suite your chuck jaws. Large enough that you get good pressure. Small enough that the jaws are not too far out.
- the tenon needs to seat on the jaws

check out a few videos: https://www.youtube.com/watch?v=XOLjer_trA8

Check your hardware
- re-tighten the jaws periodically: if they are coming loose, then you may have an issue with your chuck. Esp since you are using dry, hard wood.
- check your chuck and that the jaws are correctly installed. i.e. all 4 tightening to the same diameter
(if one or more are out of alignment, you will have issues.)

Hope that helps

[David Delo]

Not sure why Jeff didn't post pictures of the bowl in question like he did on another board but here they are.

313194313195313196

[Pat Scott]

I pictured a much bigger bowl than that. This one looks about 4"-5" diameter? It's hard to tell from the last picture, but I see two dark lines. Are these cracks? If they are there is your answer why it broke. The other thing going against you is the form itself, where it's longer than it is wide. Almost like making a hollow form, you have a lot of mass stuck out from the chuck and not much base to support it. I suspect you were taking too big of cut, or had a catch, and that was just too much force for the tenon to hold. Maybe a hollowing tool would work better instead of a gouge, even if this is side grain.

If I were making this piece, I would flatten the bottom and then make a tenon as wide as the bottom. Just cut a dovetail on the outside of the form, it doesn't need to be very deep. Then take smaller cuts and/or use a different tool. If the outside turning is already finished, just cut a shallow dovetail on the outside and leave the base a hair thicker than normal so you can reverse it after hollowing to clean up the side. Or turn the dovetail into a bead or groove or some other decoration.

[Thom Sturgill]

flatten the bottom and make a glue block. Capt Eddie has a video on that (of course). I would go with titebond rather than CA glue, but his technique works and the glue block can be mounted to a faceplate (preferred) or in a chuck.