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
========================================
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/>
========================================
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
=======================================
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
========================================
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
