Kiln for Bowl Turning

I have been rough turning bowls, sealing them with wax and also placing them in brown paper bags with the wet shavings to slow down the drying process, and they still tend to crack. I heard of someone making a homemade kiln with a mechanism to warm the inside at a slow rate to avoid cracking. Do you have information on construction of a kiln for bowls? Thank you. – Marty Mandelbaum

Tim Inman: Green wood cannot be prevented from cracking or distorting as it dries, unless the “water” is replaced by something else as it leaves the wood – like PEG, for example. When moisture leaves the cell walls in the wood, the cells shrink. Plain and simple. Controlling (slowing) the rate of shrink helps control the movement and reduces destructive cracking and the stresses that go with drying, but slow drying does not prevent dimensional changes or cracking from happening.

Partially pre-drying your blanks might be helpful. Having a kiln to more totally control the overall drying would be great. There should be internet plans aplenty! Try the AAW [American Association of Woodturners] resources for a start. Another great resource for wood info and drying is the Forest Products Research Laboratory at the University of Wisconsin, Madison. This is the motherlode for wood information. A simple solar kiln might be perfect for you, and they can tell you how to build one.

Here’s another thought, though. Some of my woodturner friends have been working with submerging their green blanks in alcohol to displace the water in the wood cells. They feel the alcohol easily exchanges with the water in the wood. They then remove the blanks after several days, and let the alcohol evaporate. They feel the alcohol dries much faster than water, of course – and leaves the blanks with less distortion and less internal stresses than air-dried wood. You might investigate this technique, too. BEWARE! Alcohol is very flammable – and it burns invisibly! You can’t see the flame when it is burning! Be careful if you try this.

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