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Clamp green and then dry?

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Greetings,

I'm still fairly new to turning and unfortunately patience hasn't been my virtue. But I had an idea and was just wondering if this might be do-able or if anyone else has already tried it....before I give it a go.
  1. Using green wet wood, turn a basic bowl to final shape and thickness.
  2. Then put a circle or band clamp around the exterior rim and perhaps a ringed form clamped into the interior of the rim to "lock in" the shape.
  3. Then air dry or put it in kiln while it's clamped.
The goal being to expedite drying time and maintain the original shape with minimal warpage and movement.

Might that work ? I'm sure the type of wood and size/shape all factor in but in general??

Regards,
Rick
 

odie

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Panning for Montana gold, with Betsy, the mule!
Only one way to find out for sure...... ! :D

Off hand, I'd suspect you could minimize the warping......but, unless the band clamp is perfectly rigid, it will allow some warping anyway.

-----odie-----
 
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I started turning a dry piece of cherry in January, then had a knee replacement in February so didn't get back to it until May. Even though it was dry it moved a lot. I've read once as you turn you release tension in the wood and you'll get some movement. I guess I'd say I agree with Odie, only a little more long winded. Sometimes just put your head down and do a lot of green blanks, it becomes fun and can become addictive. I've got a drying room with a lot of once turned bowls waiting. It's amazing how fast they accumulate. I think there are turners that sell once turned bowls if you really can't wait. It should be fun.
 

Mark Hepburn

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You may find that it simply "snaps" back into its intended shape in spite of your best efforts. Wood will tend to move no matter what you do and if you try to prevent it, you may end up with cracks instead. Just my .02 :)
 
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Putting any type of band clamp on the outside will help prevent cracking, but won't prevent warping. All of my bowls are green turned to final thickness, about 1/4 inch, then I put some stretch film around the edge to protect it as it dries, since that is the most vulnerable part, and then let them air dry. They are done moving in a week. Maybe 10 days if I turn a bit thicker. You can make a circle form, so, think cut a circle out of a piece of plywood and fit that over the outside of the bowl. It keeps the bowl under compression, which is good. If you put a circle on the inside, that puts the bowl in expansion mode and that will guarantee a crack because the bowl is trying to shrink against an unmovable form, which builds stress, and stress is relieved through cracking. I have heard of this being done, but never tried it. I prefer the warped shape. It goes with my warped personality. To me, using a kiln is forcing the wood to dry, and is an extra step, that to me is not necessary.

robo hippy
 

hockenbery

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Wood is going to move as it dries to reach equilibrium with its environment.
Most species shrink close to twice as much around the growth rings(tangential) as they do across the grown rings(radial). Wood does not shrink in the vertical direction.

So if you put a ring around a bowl with balanced grain it would dry oval with the endgrain touching the ring.

Johannes Michelson devised clamps to exaggerat the warp of wet wood to improve the shape of his cowboy hats.

He turns turns the wood quite thin clamps the headband area to get a little more ovalness and use rubber bands to get the brim to roll up a little. Then he has to put finish on it to prevent the wood from absorbing moisture and returning to the shape nature had in mind.
 
Joined
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Putting any type of band clamp on the outside will help prevent cracking, but won't prevent warping. All of my bowls are green turned to final thickness, about 1/4 inch, then I put some stretch film around the edge to protect it as it dries, since that is the most vulnerable part, and then let them air dry. They are done moving in a week. Maybe 10 days if I turn a bit thicker. You can make a circle form, so, think cut a circle out of a piece of plywood and fit that over the outside of the bowl. It keeps the bowl under compression, which is good. If you put a circle on the inside, that puts the bowl in expansion mode and that will guarantee a crack because the bowl is trying to shrink against an unmovable form, which builds stress, and stress is relieved through cracking. I have heard of this being done, but never tried it. I prefer the warped shape. It goes with my warped personality. To me, using a kiln is forcing the wood to dry, and is an extra step, that to me is not necessary.

robo hippy
Thanks robo hippy! I've seen your wrapping technique in some of your videos. And I'm fairly certain that might even have been the catalyst for this compression rig idea. I wonder though, what if the green bowl nested inside another bowl like shape fairly tight AND there was a smaller bowl like shape sitting on the inside. If it can't go out and it can't go in, would you still expect cracking?
 

Mark Hepburn

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Rick,

As Al Hockenbery described, the wood will shrink tangentially at a rate (relative to the radius) that may well assure cracking due to shrinkage. It may literally pull away from itself inside the two components that are clamping it.
 

hockenbery

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Related to your question is steam bending and bending thin spindles.the long grain of some species becomes flexible when steamed or when wet before drying. It can be bent and clamped and when dry will retain most of the bent shape.

mike Hosulak does a terrific ladle demo where he bends the handle it make it extra special.
 

hockenbery

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Size is a big consideration. The wood shrinkages are percentages, so the actual movement in a small bowl is small in distance Compared to the distance moved in a large bowl.
The dimensional movement in a 8” bowl is 1/2 the dimensional movement in a 16” bowl.

I can usually dry a 3” limb without it cracking.
Almost never dry a 5” limn without it developing radial cracks.
 

Mark Hepburn

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Greetings,

I'm still fairly new to turning and unfortunately patience hasn't been my virtue. But I had an idea and was just wondering if this might be do-able or if anyone else has already tried it....before I give it a go.
  1. Using green wet wood, turn a basic bowl to final shape and thickness.
  2. Then put a circle or band clamp around the exterior rim and perhaps a ringed form clamped into the interior of the rim to "lock in" the shape.
  3. Then air dry or put it in kiln while it's clamped.
The goal being to expedite drying time and maintain the original shape with minimal warpage and movement.

Might that work ? I'm sure the type of wood and size/shape all factor in but in general??

Regards,
Rick

By the way Rick, i like the bowl in your avatar photo. Any chance you could post a larger photo?
 
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Wood MOVES . A basic statement I know but it is a given fact and no amount of clamps, screws, glue or other restrictions will stop it. This can be observed in tables where the top has been glued or screwed cross grain to the supports. Eventually it will crack due to seasonal stresses. Physical restraints may stop or slow movement for a while but not permanently.
To make it work for you learn how to deal with it by drying or using stable wood (boy is that a misnomer), or learn to live with the oval or out of round shapes.
 
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In the ship building trade steaming the wood to relax the fibers and then clamping and bending the boards to conform to the shape needed is a common process.
The wood still moves when it dries but they take that into consideration with the cut of the timbers and its wood grain orientation. There are a number of wood turners that steam or boil there bowl blanks to release internal stresses in the wood billets.
 
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I would think that if you tried to dry one bowl inside another, and it was a close fit, the fit would be a lot closer when they were dry, making it almost impossible to remove. I think a plywood ring would be best bet.

robo hippy
 
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I started with segmented turning, not really knowing/understanding the whole green wood side of things. Over time I developed my plan, which included bagging and allowing to dry. It didn't help the anxiousness of wanting those first pieces to dry so I could finish, though. There are ways to approach reducing the "cycle time", but after you get some inventory built up and some stair-step to the timing, you will most likely settle into the "rhythm". I do some once-turned stuff now, and that's what I'd recommend vs trying to speed up the drying process. For items small enough you could experiment with microwave drying to speed things up.
 
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I'm also impatient. I hated leaving unfinished bowls to dry for ages. I've used crystal cat litter to "speed dry" wet bowls with good results. I put a trash can liner inside a 5 gallon bucket and add about 4 inches of crystal cat litter, put the bowl in on its side and then pour in the litter until the bowl has a few inches on top. On an 8-10 inch bowl gets pretty dry in two weeks. Depending on what sort of silica crystals you use, you may be able to follow a manufacturer's drying procedure and reuse them. I didn't bother.

But even that much wait is too long for me and now my wet turnings goes to final thickness in one session.
 

John Jordan

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Liam O'Neil places a stick snugly across the grain of open bowls after turning green. It keeps the wood movement from "squeezing" the bowl more oval than wood movement would account for. It works well for Liam and I did it a few times years ago. I don't turn many bowls, and don't mind the movement when I do.

A relatively thin bowl will dry in the air in a day or two. I usually put my hollow pieces in a cabinet to slow the drying a little.

John

PS Bob Stocksdale often put metal hose clamps around the top of his bowls. He was convinced it worked and was the original and great decorative bowl turner.
 
Last edited:

Dennis J Gooding

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Greetings,

I'm still fairly new to turning and unfortunately patience hasn't been my virtue. But I had an idea and was just wondering if this might be do-able or if anyone else has already tried it....before I give it a go.
  1. Using green wet wood, turn a basic bowl to final shape and thickness.
  2. Then put a circle or band clamp around the exterior rim and perhaps a ringed form clamped into the interior of the rim to "lock in" the shape.
  3. Then air dry or put it in kiln while it's clamped.
The goal being to expedite drying time and maintain the original shape with minimal warpage and movement.

Might that work ? I'm sure the type of wood and size/shape all factor in but in general??

Regards,
Rick

The problem with a band clamp as described is that it is not very elastic. As soon as the wood shrinks a tiny bit the tension in the band clamp falls to zero. A better alternative would be to wrap many stretched rubber bands around the lip of the bowl to maintain a squeezing force as the bowl shrinks. That technique is used a lot in wooden hat making. Another method, also used in hat making, is to build a jig out of springy wood as follows: the jig has two flat parallel vertical pieces separated by the nominal diameter of the bowl and fixed rigidly at the bottom. A drawbar spans the two uprights and can be tightened with wingnuts. With the bowl positioned between the tops of the uprights, the drawbar is tightened to bend the uprights inward and put pressure on the bowl. The uprights act as a spring and will maintain a slowly decreasing pressure as the bowl shrinks.
 
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