Wood will move (long-winded response)
Dominic Greco in Richboro, PA
>Fred,
No matter what you do, the wood will move. Changes in the humidity, or temperature will cause it to move. Since we're working with wet wood, it will distort as it drys.
The old air drying regimen of allowing bowl to sit for months (or years) at a time has it roots in that you give the wood time to get slowly rid of the excess moisture. We make the roughed out form thick so that you can accommodate the fact that the wood has indeed moved. But you left yourself enough excess (hopefully!) to compensate for that.
IMHO, trying to stop the movement of wood is a recipe for disaster. The stress generated by the wood moving has to go somewhere. Usually this will result in a crack. That is why woodworker's in the beginning of recorded history invented frame and panel construction. The solid wood panel is allowed to move with the seasonal changes in temperature.
I see something like this all the time as an mechanical engineer. A piece of equipment has a component that breaks under stress. So someone suggests making that component stronger. After you do that, the support structure around the component fails. Like I said, the stress had to go somewhere.
However, I know of several turners who insert 1/4" plywood disks in the base of their bowls. This limits the movement of the wood at the base. This technique works pretty well. But it doesn't stop it at the rim of the bowl. We minimize the movement by using dried wood, or aligning the grain (as in segmented work) so that the wood moves in the same direction.
Mike Schwing has a point too. Why limit it?If you're into turning green wood bowls, you know that they'll warp. That's part of their beauty. They get this "flower like" look that is very appealing.
Hope I haven't gotten too far afield on this one and that you've gotten my point.
See ya around,
Dominic
