Microwave drying green wood

[Phily]

Just a heads up that there is a bit of a discussion on microwave drying of green timber in the woodturning general forum - microwave drying - using paper bags.
Cheers
Phil

[issatree]

Hi Phil,
Many Moons ago a chap started drying wood in his MW.
Worked out a Formula.
So you need a set of sensitive Scales in Grams.
Take MW outside, as it will smell the house out.
Weigh the wood, & write the weight on it.
On High, you dry it out at 1min. for every 100Grams.
Give it a rest, to cool down a bit, then weigh & write again, repeat the same until there is no difference in the weight.

He also made a kind of Kiln, out of glass. He had to put a sheet of ply ??? over the wood as it was getting to hot.
He also ran 2 Fans out of a Computer, hooked up to a couple of Solar Cells for power to them, to take the heat out.
Dried the wood in an amazing short time.

[Phily]

I've tried this technique on a few different woods. No problem at all with camphor laurel (which is a pretty stable timber), Oak was OK though moved quite a bit, Elm has been really good but Cherry just about shattered! With the feedback from the other discussion there might be benefit in wrapping the timber in newspaper or cloth to help even out the drying process and thus reduce cracking. I have a fair bit of green timber (approx 3 to 4 tons!) including freshly cut Manchurian Pear. I need to get some batteries for my scales, but hopefully later this week I'll be able to give your suggestion a go combined with wrapping. I'll also do the same without wrapping and post some photo's of the before and afters.

Ref the kiln, I converted our greenhouse into a solar kiln leaving a couple of windows slightly open to let the moisture out. It has certainly reduced the drying time - most timbers are ready for use from green within 6 to 9 months. Though again there is a great deal of variation. Fruit woods don't like the process at all. The Japanese Cyprus didn't move or crack one bit. Ash and Elm handle it OK, but Oak is a bit hit or miss (though that may have something to do with the way the blocks were cut). Definitely going to wrap all future Cherry blocks before drying.

I'll let you know how I go.

Cheers
Phil

[delbs]

Very interested in this process. Ive just posted a question as ive got a large stack of manchurion pear also thatd id like to use sooner rather than 2 or 3 years away . unfortunate that the fruit woods dont like this process.

Cheers
Nathan

[Phily]

Its the Manchurian that I am most interested in working out a good technique as I love turning it! Fingers crossed the wrapped zap approach does the trick :U

[shedbound]

I have tried this method with pen blanks and a few bowl blanks, with the timbers that a more prone to splitting I sometimes put a 1/2 a mug of water in the microwave with the timber for the first part of the drying and find it helps (sometimes) , I dont know why whether it adds moisture to the environment almost like steam drying, or just stops the timber copping the full zap. No harm in trying. be interested to hear others thoughts.

[delbs]

So you just wrap each piece completely in a page of newspaper? And then put it back to dry where its currently living? Ive got a whole tree and so far i really enjoy turning it. The trunk of mine was a bit rotten so ive dressed the larger bits on the jointer and its spalted. Looks fantastic so im slicing it up for some box lids etc 349992

[shedbound]

The bowl blanks I have turned green from a 1/2 log tend to want to warp even wrapped and in a box of the shavings, or it goes mouldy. I dont have much luck with green stuff. But it is fun to green turn a bowl as thin as possible and warp it deliberatly in the microwave, makes for some intersting shaped bowls.

[Phily]

Nice spalting. Is that Manchurian?
I like the idea of having a cup of water in the MW - may serve to reduce the intensity of the nuke as well as stopping the surface from drying too quickly. Same principle I guess to wrapping the timber. Ummm, another experiment!!!

[Kidbee]

For what it is worth, I pulled the following from another forum:-

"Roger I have used microwave drying quite a bit. My method came from someone on the web so it isn't original to me. I put whatever I am drying in a plastic garbage bag and and fold the top under the turning. I microwave on high for two minutes then take it out of the bag and cover with something to keep it from cooling to fast, in the shop I use an old Carhart coat. I let it cool for 5 minuets then turn the bag inside out so there will be a dry spot for the turning. I also weigh and record the weight. You need to be pretty persistent in the process to get good results. It takes several cycles to get it dry, the bowl stays hot and heavy gloves are recommended. There is a lot of steam generated in the bag so you need to use caution with that. I have dried bowls up to 14" and smaller things like lids that tend to warp a lot. It is a lot of trouble but it does produce good results . I have dried oak, cherry, maple and walnut and maybe others. One thing that can happen is the turning may get two dry, it is kind of a guess when it is dry enough. It usually takes 8 to 10 cycles, I watch the difference weigh between cycles starts to drop off and that is when I usually stop. I let it set in the shop enviorment for at least three days to see how it reacts, sometimes it will gain weight (to dry) and sometimes it will loose weight (not dry enough) . It is quite a bit of work but sometimes I need something next week instead of a couple months down the road.
You may need to adjust the time on for different microwaves, mine is an old one and I don't have any idea of the wattage. The person who gave me this method used a seal plastic bag, when it swelled but didn't burst was what he used for the cook time. I always use full power. I have tried other processes but this one gives the best results.
edit: My microwave doesn't have a turntable, sometimes I take out the glass dish to get extra room.

[Phily]

Thanks Kidbee for the detailed response. Great information. A couple of questions: what is a "Carhart coat" and, once you have finished nuking the piece do you leave it for the 3 days still in the bag or in the open air?. You've convinced me to use this technique for one of the blocks in my technique comparison test!!!
Cheers
Phil