Drying Bowl and Platter Blanks

Rough-turn the pieces before drying for better results. August 30, 2005

Question
I am in the process of building a small kiln enclosure for drying platter blanks using an Ebac LD800 unit. The approx size of the unit is 36" wide x 32" tall x 8' long. This will give me approximately 6' of drying space to place platter blanks. My question is this: would I get better drying results by placing the square, stickered blanks to be dried or better to rough-turn and leave enough thickness to later (after drying) finish-turn them to final shape/thickness? All of these blanks are 6/4 thicknesses x 24" square max. I’m using hard maple and it's all sapwood, no heartwood.

My other thought would be to place the 6/4 x 16"-24" wide "slabs" x 6' long in the kiln for drying. I am wondering if my ideas are doable or do I need to change my thinking? For the past four years I've been rough-turning platters, spraying with real-lemon, then anchor sealing all endgrain, stickering for 8-10 months, then re-turning/finishing. This has worked well, but the lead time is so long. Any help will be greatly appreciated.

Forum Responses
(Sawing and Drying Forum)
From contributor Y:
I would suggest rough turning the blanks. There will fewer problems and besides, the drying time will be much less.


From the original questioner:
I have a correction to make to my original post. I stated that the blanks were 6/4 and that is wrong - the blanks are 10/4, 2 1/2" thick. Will this error change anything?

From contributor G:
I dry approximately 90 rough-turned bowls and 50 plates in an Ebac kiln. My secret is spraying my most unstable woods (madrone and fruit wood) with water every day. Maple, though, is more susceptible to mildew in my area of the country (Seattle), so I don't spray the maple rough-turned stuff. It lets water escape a lot better than madrone or cherry.

The key is to control the humidity by venting and temperature. There's another thing I've started doing, too, which is air-drying a bit before trying to let the kiln do all the work. What you have to be careful of is case hardening, where the inside of your platter blanks are holding water you can't easily detect, without jamming a sensor into the plate.

You think that it's at 6 MC, bring it inside, turn it, and you will have a warped plate that's worthless of turned thin or in need of turning again if there's room. I've had to build another drying shed with a heater and dehumidifier to hold and keep what the kiln has done to my rough dried and final dried bowls and plates. I turn so many that there's no room inside our small house.

I couldn't do without a moisture meter and the knowledge that you'll loose all your drying work if you don't keep track of the humidity in the place where you store your roughed turned and final turned work.


From contributor E:
The key to drying anything made of wood is to control the relationship between the stresses that build during drying and the strength of the wood. Kiln schedules do this by moderating the rate of moisture loss from the wood by controlling RH and temperature. You start out with low rates of loss and gradually build to higher rates as the wood gets drier and stronger.

Unfortunately for your situation, kiln schedules are based on single (sometimes similar) species of wood in 4/4 and 8/4 dimensions. When you start trying to dry multiple species at the same time, it becomes difficult to say exactly how fast the pieces can be dried at any particular moment without damaging the less strong species. Rough turning your blanks means that the stresses set up by drying will not be the same magnitude as in a solid, thick chunk, thus it becomes a safeguard that makes good sense.

The best guideline beyond that would be to use a schedule for 8/4 thicknesses of the most difficult wood that you are drying in a particular load.

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