To turn green wood into bowls is not a mystery and there are tons of how-tos on the subject Excellent DVD’s on the process are available at Amazon.com by well known production turners like:
The basics of turning green wood is that wood is wet and as it dries the stresses that are encountered in the drying process cause the wood to warp and possibly crack.
Another excellent resource is the book:
Some things to consider is that a large chunk from the trunk of the tree is much more stable than a piece from a branch. The branch grows horizontally and to resist the pull of gravity it grows in a fundamentally different way than the trunk does. So wood choice, and location in the tree has a huge impact on wood movement.
Also how quickly the wood dries will change the stress in the wood. The general rule of thumb is that wood dried at a lower rate will be better than wood dried at a much higher rate. Often kiln dried lumber is still full of stress and it warps when you cut into it. When you air dry wood the generally accepted rate is 1 year of drying time for every 1 inch of thickness in the wood. But when the wood is very thick 4+ inches the inside of the wood may never dry.
All of this also doesn’t take into account the pith, the heartwood, and sapwood of the tree. All of those locations have different densities as well.
So when it comes to bowls we are faced with a wet chunk of wood that deep inside has moisture. So the first order of business is to shape the bowl and have a UNIFORM thickness throughout the walls. Also you’re better off not using wood that has any pith in it or the pith will have to get cut out, as the pith is usually where the cracks propagate.
As you rough turn a bowl, keep in mind approximately 10% wall thickness for every inch in diameter the bowl is. If you have an 18 inch bowl that means that your wall thickness on a rough turned bowl is almost 2 inches thick.
Once you rough turn a bowl then the question is how do you slow down the drying times so that the wood doesn’t pull itself apart. Many people pack bowls in the shavings that you turned from the bowl. Others put the bowls in paper bags, etc… We coat our bowls with a green wood sealer after we date the blank. We then put the bowl aside for drying.
After the bowl is dry you can final turn the bowl to the thickness that you want.
Many people investigate other procedures to speed the process up. Boiling bowls, microwaving, using strange potions and brews, and even kiln drying them. All have pros and cons in the process.
The best advice I can give you is that don’t invest a whole ton of time and emotional capital in a single piece of wood. Be prolific, turn tons of bowls, and this way if a few happen to break your heart will be fine as well.
Also one other method is to turn green wood as thinly as possible. The drying time is accelerated and if the wood moves a little bit it’s part of the charm of the bowl. Experiment and see what works for you.
- Controlling Wood Movement: The Drying Process (core77.com)
- Bangari Interview: Woodworker and Chef Felisha Wild (bangaricontentgallery.com)
- Turning Wood Platters before Wood Beads (woodbeadti.me)
- Wood Drying Forum Kilndrying.org Passes 51,000 Page Views (prweb.com)