|This is as much a tip on the value of the rec.crafts.woodturning
newsgroup as a resource as it is on microwaving wood to accelerate drying.
I'll present my original posted question as well as the unedited responses.
As you can see, opinions are somewhat different on the best approach.
I received 5 responses from all over the world.
Most of my turning to date has been with green wood and the day after
I create a bowl, it ends up warped (varying degrees with each wood).
Being new to turning I don't have the patience to rough turn a bowl and
let it sit to dry for many months so I'm beginning to experiment with microwaving.
My first couple worked good but I'm sure some of you have experience
or advice. Some specific questions I have include:
-high power or low?
-how hot can wood get before I should stop?
-microwave immediately after initial turning or let it sit a
few days then microwave?
Now the Responses...
For the small items I dry in the microwave, I begin by weighing and
recording the weight. I dry it in a plastic bag for 10 minutes on
"DEFROST". Take the bag and hot wood to shop and shake out the water
from the bag. Replace the wood in the sealed (twisted end) bag and
leave the wood to cool. Perhaps overnight. I'll run it through this
process 2 or 3 times and then weigh the wood when it is cool.
Dried (?)weight: 320 gms
80/320 X 100 = 25% weight loss
By measuring the weight I keep track of how much water has been removed.
I think keeping the drying wood during the drying process in the plastic
bag helps to reducing the checking in the wood. I recently dried
some Hawthorne which was soaking wet with spring sap and it turned out
Almost everyone has their own formula for doing this. Here is how I
1. Rough turn just as if you were going to put it on the shelf for
a few months.
2. Put in a brown grocery sack and put in the microwave. The grocery
sack helps protect the microwave and also sort of controls the moisture.
3. Set microwave on high for three minutes.
4. Remove from microwave, remove from brown paper bag, and let cool,
at least 30 minuted until it is cool to the touch.
5. Repeat steps 2, 3, and 4 as many times as necessary until there
is very little or no moisture on the outside of the bowl when you remove
it from the microwave. Some people weight them, but I just sort of listen
to the wood.
Generally takes about three or four cycles depending upon how wet the
wood is. Use a new paper bag for each cycle.
6. Allow to cool, final turn, sand and finish.
With a little practice, you'll work out your own method of doing this
that works for you.
I do pretty much what Fred does.
(1) After roughing to 3/4", I put the bowl into the microwave on defost
for 2 to 3 minutes.
(2) I leave it in the microwave for at least 10 minutes, then take
it out and let it completely cool.
(3) After 2 or 3 cycles on defrost, I procede to high for as many cycles
as it takes. You can tell when it is dry just by feeling and even the smell
is different. (It no longer beads up moisture.)
(4) Then I usually let it sit for 3 or 4 days to reach EMC (equilibrium
moisture content) before finish turning and finishing.
Every species of wood is a little different and reacts a little different.
The microwave is also good for getting rid of insects. I turn quite a bit
of wormy red maple. A minute or two on defrost will kill powder post beetles
or any other insect.
Every one does it a little different. If it works for you it's right
May your next turning be your best,
Marshall's Woodturning Homepage at
I've tried the microwave on a few bowls myself and have had best results
with it set on defrost weighing the bowl first then weighing it again after
about 15 mins. leaving it to cool down the starting the process again until
you get the same weight before and after keep the bevel rubbing
I have tried the microwave method. What I did was to turn a 9" diameter
maple salad bowl green to 1/2" thick walls, and left the spigot on the
bottom for rechucking later. Then I microwaved it on low(25%) for 3 to
5 minutes. Weigh the bowl on a kitchen scale before you start. When you
take it out of the microwave it will be steaming. Let it cool, then weigh
it again. It should have lost a little weight. Repeat the process until
it stops losing weight. That's when it's reached its moisture equilibrium
and is pretty stabile. Mine developed surface checks, which I turned away
after re-chucking and turning to 1/4" thick. It turned out ok. Somewhere
I read that someone leaves the bowl to cool overnight between turns in
the microwave. Not a bad idea. If you get too impatient you can damage
the wood from too-fast a drying process.
A friend in Australia does the freeze dried method. He turns the bowl
to final dimensions, puts the finish on and everything, then puts in a
plastic bag and into the freezer overnight. Takes it out of freezer and
out of bag and thaws
it. Then puts it (without bag) into the fridge for 2 weeks and it's
done. (Refrigerators are dehumifiers).I've seen photos of his work,
and it works great. Very little warping. I haven't tried it myself yet.
Pretty much all green wood will warp at least a little. When I want a project
not to warp, I buy dry.
By the way, don't microwave burls, unless you want a lot of distortion.
I tried it, and everything pruned and shrunk at different rates. What I
ended up with was a funky little vase that looked more like 3rd grade pottery
(Look, Dad, an
ashtray!!!!) than what I started, but I actually like it for its unique
-Jim Gott (Jgtimp@aol.com)
Try this URL
Rex Haslip, Auckland, New Zealand