Hollow form concept & question...

[Phillip H Smith]

At our CNY Turners Club meeting last week, one of the "Show and Tellers" had several "fake" hollow forms. What I mean by that is: He'd followed an article (I think in the AAW magazine) about how to make a "fake" hollow form by cutting a blank in half, turning the insides of each piece, then putting the whole thing back together. He'd done a great job on several pieces by turning a lipped seam at the center and then used several burned lines to hide the center cut.

I'd like to give this a try, somewhat because I want to make a hollow form for a gift.... and --sadly-- am presently unable to "hide" any more expensive tool purchases from my local comptroller (er...LOML).

So....here's my question: If I take a 4-5" diameter cherry limb, turn it into a nice cylinder, then cut it in half and hollow out the two parts, do I have to be concerned about the pith causing a crack? Obviously, I'd be turning away most of the pith in the bottom half, and eliminating it all together in the top. But since the pith is to be avoided when making a bowl...how is that handled with a "real" hollowform? In other words, how do you keep the bottom from cracking?

[TYLER WOOD]

The HF I just posted still has the pith in it. It was cut about 6 weeks ago, living in a desert area (almost) makes a difference of course, but it hasn't moved very much yet. I got a little cracking, but they were hairline at worst.

I would suggest you try it on a dryer piece of wood or something without pith in it personally. I am very worried about my HF cracking up as the pith is off centered, but if it does oh well.

[Harvey M. Taylor]

Hi Phillip.
Just a dumb suggestion from someone that has never turned a hollow form. When you are almost there, drill out the pith and insert a plug of the same or contrasting wood and finish it up. Probably look better if you used contrasting wood, as it would be hard to hide a similar wood plug. Just a free thought, take it for what it is worth, Max

[Paul Engle]

You could soak it with thin CA glue before you turn it to final size.

[Tom Keen]

I suggest you try to find an old dry limb, But if you want to use green wood, hollow it out as thin as you can and then if you see little hairline cracks use CA. If they are on the bottom I wouldnt worry about it, but CA will darken cherry.. be carefull where you use it. Really soak your piece with Danish Oil. It seems to help stablize the wood..

Tom

[Allen Neighbors]

Good suggestions, all.
In addition, if you turn green (not cured) wood, turn the bottom a little thinner than the sides.. this will relieve some of the stresses as it dries. One way to do this is to plan the bottom before you hollow, and then, when you finish the bottom, concave it, so that it's thinner.

[Steve Trauthwein]

Try to find some wood other than limbs as it is all reactionary wood and more prone to movement. Anything from the trunk of the tree would be fine. I find different woods move differently. Walnut with a pith is absolutely the worst, in my limited experience. Your mileage may vary.

Regards, Steve

[joe greiner]

Cracking occurs not so much because the pith is present, but because the outside tries to shrink against it and the pith pushes back. If the wood isn't already cracked, the sooner you get to a dome shape, the better, because the outside shrinks against air and the air can't push back. The outer fibers then flex along the grain. As Al suggests, a thin wall near the bottom makes flexing easier for the wood so it won't crack there either.

Joe

[byron constantine]

I have done several vases this way. It is the only way as i don't have
hollowing tools. I got the idea from a turner in the UK,works real good.
Make a good clean joint and use some small beads and the joint
dissappears. You can also add a piece of contrasting wood between the
halfs.
Byron

[Bernie Weishapl]

Phillip I turn a lot of bowls and HF's with the pith in them. You can do two things. Turn the HF to final size. Then before finishing the bottom either soak it with CA or epoxy. I mix 30 min epoxy and once mixed I add Denatured alcohol till it is the consistancy of milk. I paint this on and let it soak in. Let it dry for 24 hrs. Then go and finish turning the bottom. Do a search for a China Berry bowl and in the 3rd picture you will see the pith in it. It went straight thru to the other side. I used the epoxy cocktail as I call it on it and it did not crack at all. One thing I learned from another 35 yr turner is that the pith should be pretty much but not exactly on center to make it look good.