Woodturners of south west florida
Tips:Microwaving Wood
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.

Original Question...
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?

Tony Aloise

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.
     Initial weight:      400 gms
     Dried (?)weight:  320 gms
     Difference:           80 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 well. 

Derek Claridge
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Hello Tony,
Almost everyone has their own formula for doing this. Here is how I do it:
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.

Fred Holder
<http://www.fholder.com/>
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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 for you! 

May your next turning be your best, 
Marshall 
Marshall's Woodturning Homepage at
http://members.tripod.com/~mgorrow/index.html 
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hi Tony
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

bob
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Hi, Tony
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 character.

-Jim Gott (Jgtimp@aol.com)
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Try this URL
http://homepages.ihug.co.nz/~rhaslip/microwav.htm

Rex Haslip, Auckland, New Zealand

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