Finishing a Root Ball

[Alan Gan]

That first picture scares me. The tenon is too deep and will bottom out in your jaws. Also it looks like there is a big pie-shaped chunk just waiting to break out.

Thanks Pat, I now know what Charlie meant by scary. I missed it due to my lack of experience. That is if Charlie was talking about the Tenon...

I do need to ask Pat, is the tenon not supposed to be bottomed out into the chuck?

As soon as I chucked it up I knew there was going to be problem, it was like a sponge. As I was tightening down the jaws they just squeezed on the holes. Turned at 100 and in less than 30 seconds bowl was loose, the defects in the Tenon were worm holes. I remounted it back on the Face plate and removed the tenon, ended up with one worm hole and one worm that I extracted from the blank.

So now I am a bit stuck, the 1 worm hole is right at the tenon area and I am not sure what to do at this point. The hole is deep, at least over an inch deep into the blank. Not sure how to chuck it up to turn the inside???

[Eric Gourieux]

Alan, the tenon is not supposed to bottom out. The front edge of the chuck jaws should fit solidly against the base of your piece, and there should be good contact between the outside of the tenon and the inside of the jaws AND between the front edge of the jaws and the bottom of the wood. It looks like your tenon is long enough that it may prevent good contact between the front edge of the jaws and the bottom of the piece. As for re-mounting, you have a few options:

1. screw to a faceplate, turn and hollow, reverse chuck and turn the bottom. You will sacrifice some wood, due to the screws in the faceplate.
2. turn another tenon to the proper size. If this is one of your first with a tenon, you will find that, sometimes, you have to sacrifice some wood to be able to mount it safely. That's a killer, I know.
3. glue your piece to a more solid piece of wood you are willing to sacrifice (called a "glue block") and turn your tenon on the glue block. Then, mount the glue block end into your chuck, turn and hollow. When you reverse your piece, you can turn off the glue block and finish the bottom of the piece. There are various ways of accomplishing this, and you can find numerous threads here on SMC that discuss this.

If the wood is spongy, or punky, you can try saturating the tenon with thin CA glue to give it some strength.

And the most important thing you can do when turning a piece like this is WEAR A GOOD FACESHIELD and stay out of the line of fire as much as possible.

[charlie knighton]

actually I did not notice the tendon, I thought that the area in question was like a fish you caught, hold it close to the camera and it appears larger, I was scared of the bark inclusions...........hope you post the finished piece, it looks as it will be a winner

when I first started doing hollow forms I did not know about bottoming out, luckly I did not kill myself, and luckly I went to see Nick Cook demo the elbo tool....it was quite the revolation........Nick is still one of my waypoints in the curve

about that time one-way came out with the "tower jaws"

[Pat Scott]

What Eric said.

My choice would be #2. Completely remove the current tenon and cut a new bigger tenon out of solid wood. You'll lose some depth off the bottom, but not much.

The yellow arrow is pointing to part of the crack. The red arrow points to a tool mark that is just past the crack. If you have bigger jaws, you could cut a new tenon and stop at the tool mark (red arrow) or just a bit bigger. Make the tenon 3/8" deep (which is plenty), make sure you have a flat spot for the top of the jaws to set against (2nd picture, blue arrow), and you're good to go. My Vicmarc dovetail jaws are roughly 1/2" deep, which means a tenon can never be longer than that. Remember, longer does not mean stronger.
DSCN2242_.jpg 3-1-2015 8-44-06 AM.jpg
The top of the chuck jaws need to sit square against the bottom of the bowl (blue arrow), you never want the tenon to touch the bottom of the jaws. If this happens, it won't run true and you are more likely to have a failure, like the tenon snapping off. A larger diameter tenon is always stronger than a longer tenon. The reason is you have longer side grain fibers.

[charlie knighton]

Pat, your picture #2 is well done, also your observation that a larger diameter tendon is always stronger is something we all should follow. good pictures , like your arrows