Hollow form question: re-turning.

[Dan Forman]

So I'm turning an apple hollow form. The bowls from this wood that I have rough turned warped quite a bit, so I anticipate the same for the HF. How do I remount to clean up the tenon so that I can place it in the chuck?

I read Steve's tutorial, where he said to use expansion jaws in the top hole, but I expect it to be quite out of round too. I have used a jam chuck for bowls, do you make a long, skinny jam chuck for hollow forms?

Thanks,

Dan

[Steve Schlumpf]

Dan - just my experience but the opening hole into the hollow form will warp into an oval/oblong shape. I have found it easiest to use the smaller jaws on my chuck to expand into that warped opening. With the tailstock making contact on the original center - I spin the hollow form to make sure it is fairly close to centered. If not - loosen up the chuck, rotate the turning about 90* and try again. You will find a point that the warped sides are about even each side of the rotation. Just one of those things that gets easier with doing...

[Richard Madden]

do you make a long, skinny jam chuck for hollow forms?

Thanks,

Dan

That's what I do. I turned a scrap piece with a taper to fit different openings. Hopefully, you have the center of the tenon marked for the live center.

[David E Keller]

I do it the way Steve described, but I'm sure there are a lot of ways to skin that cat.

[Richard Bell CA]

Dan:

I use a bull nose center in the hole (tailstock end) and a drive center on the tenon end.

Richard

[Jim Burr]

+1 on Steve's plan...remember you have the point from your tail stock center. This gives you an exact center to work from. So if your using a donut or jamb chuck...you always have a reference point. Good luck!!

[George Guadiane]

If the center is very far off, I put the piece between centers again. I use a cone in the opening and the live center pin in the the tenon end. I then return the tenon to make the opening as close to center as possible.
I find this works about 90+ % of the time. The other 10% the distortion is too great.

[Bill Bolen]

+3 on Steve'smethod.

[Thomas Canfield]

I returned a Cherry Laurel potpourrie piece tenon earlier this week using a PSI Super Drive Center (Stub center knockoff) to drive the inside and tailstock on the tenon. The drive center has a spring loaded center pin and multiple teeth and worked well on the inside bottom. Of course, this was only about 2 1/2" deep. On a larger depth, I think that a jam chuck in the opening and the live center on the tenon would be my choice to only true up the tenon and close area, and then reverse it using the new tenon to continue work on the outside and inside. The jam in a small opening would support the piece and provide enough contact to drive for light cuts on the tenon area.

[Dan Forman]

Thanks for the tips. For now I'm just hoping that it doesn't self destruct (with or without my help) by the time it's ready for a second go. :)

[Mark Levitski]

Craft Supplies sells a "Woodchucker Mandrel" that I've seen Mahoney describe and use on one of his videos for this purpose, though it looks like this could be somehow fabricated at home. It utilizes a bullnose or cone for the opening as suggested here in this thread (mounted on a small faceplate).

Really, once you figure out how to get the tenon back in to round and remount in a chuck, you're home free. And there are a number of ways to do that depending on the form. The trick is to leave just enough thickness when roughing so that you have something left after getting back in to round for finishing.

Steve, what small jaws do you usually use, and do you primarily use them and the chuck as a jam chuck? It seems that by expanding jaws into a somewhat warped opening, you would be relying on the friction/jam moreso than the expanded jaws? And would one need to be careful of expanding the jaws enough to break out that opening, or would there be enough beef in the roughout to prevent that?

[Steve Schlumpf]

Mark - depending on the form, I use either the #2 or #1 step jaws on my Talon chuck. When mounting the hollow form to the chuck - I open the jaws just enough to grab the form but, seeing as how we are talking about roughed out forms, there is some extra wood there for the jaws bite into. Expand the jaws just enough to turn the form - the weight of the piece is actually supported by the tailstock.

Usually, because of the piece being warped, you have to play games a little bit when centering. All I do, once the form is on the lathe, is rotate the turning by hand to make sure the piece is not totally lop-sided. If it is, simple loosen the chuck, turn the form a little bit and try again.