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microwaving greenwood?

C

Charlie Harley

Joined
Jun 20, 2006
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Location
Cincinnati, OH
I've heard that some folks microwave small bowls and such that have been turned green in order to speed drying. Any truth or merit to this practice?

It's hard for me to look at a paper bag for three months without wanting to finish the project.
 
microwaving green wood

I have done this rarely on small pieces with good luck.I have read about others that do it alot. They weigh the wood, cook it for a minute to several at a time and re -weigh till the weight goes down to the level they want it. you can actually burn it if you cook too long I have read. I guess to really be exact you need to know the percentage of moisture that you start with and the percentage of moisture that woods will normally equilibrate to in your area. I would suggest you start out with a small piece and figure out what percentage of the initial weight you would have to get rid of to be dry, without burning it or getting it too dry( for your area). Then you can just follow the same procedure with any piece. I have also read about boiling the rough ened pieces to get rid of the water. You boil it for 1 hour for each inch of thickness. You still have to keep the pieces in bags but it cuts down on the time greatly as the water is now out side the cell walls as tre water is vaporized by the heating up same as with the microwave. If I run across the articles I'll post them later for better details. I have all kinds of paper bags with pieces that I've roughed. I keep forgetting whats in them . I have started dating them , so I immediately know at a glance how long that they've "aged".
Frank
 
Yes and it does speed drying. I do have questions on it's effects on warpage/cracking. But I'm still trying it

The safest formula appears to be 2 minutes on defrost, then leave the blank in the oven for at least 20 minutes. Remove and weigh.

Repeat until weight loss stops
 
Chairlie
N7's recipe is a good one, 2 minutes on defrost, and leave it rest for a while. I think its best to run maybe 2 cycles per day for a week. Even if you don't have a moisture meter or a scale you'll be able to feel the piece does not get as warm in the later cycles so you know you are approaching a satisfactory dry-ness.

I will nuke a bowl if its been roughed for say 3 months. So instead of waiting 6 months or a year to finish turn the piece I can rush it. I did this often when I first started turning but now the inventory of rough bowls is to the point were there are other choices so rushing the drying process is not as much an issue. I would encourage you (if you are a new turner) to resist the desire to rush drying and just turn more rough out and in 6 to 9 months you won't have to think about this topic.

On the other hand the microwave is a great way to rush cure small pieces for pens and stoppers that you cut from bowl scraps. If you don't deal with those piece right away they will split up and be wasted.

Frank
 
I don't use it anymore for finish turn green bowls because most of mine are about 1/4" thick and they dry quite nicely in a day or two. I have done some rough turned bowls. I heat them up until they are warm and let them completely cool. I never go long enough to make them really hot to the touch. My early cycles are about a minute or so and later cycles go to 2 minute or more. I have a small weak microwave so you cycles may vary.
I use it a fair amount to dry boxes. I rough turn them to about 1/2" depending on how big they are and what wood. The I dry them similar to above but longer periods as the wood gets dry. I moniter the tenons closely as this where they usually start to crack. I have tried setting them upright with the tenon down on a wet rag while they are going through the cool down cycle. this has helped.
I'm not a big fan of microwave drying. I feel slow drying is safer but sometimes you just have to get a project done. My boxes are a little to high in moisture content coming directly from the shop so I like to dry them to keep them from changing shape too much when they go to my gallery which has much lower humidity than my shop or my house.
 
I use the microwave almost exclusively. There is no one recipe for microwave dring it will all depend on your wood and your unit. depending on the stage of turning or necessary dryness will tell me how long to nuke it. There is some distortion and some cracking depending on the piece but that is true of every drying method and mopre a function of the wood than the drying method. There are inherent dangers in this method but that is to be expected for anything you put in your microwave be it be it a cup of coffee, a plastic plate of leftovers or a big hunk of maple.
 
I've used the microwave occasionally to hasten the drying process. It's usually worked well, with the exception of one of my early attempts when I started to cook the inside. (it did give me an interesting 'look' however...) I don't get into the weighing and timing and trying to calculate moisture content. I typically 'nuke it' several times, letting it cool in between and then let it air dry. I figure it saves me several weeks/months in drying time...

Brian
 
I should warn you, I've ruined 2 pieces. One because I was cooking it longer than I do now and sap pocket apparently turned to steam. Burned a black hole in the side of the vessel and almost burned me.
The second time was me. I put the microwave on more time than usual for some dumb reason and was watching it when I got a phone call, the phones upstairs. I was talking on the phone and thought "who's been cooking popcorn, Oh #@%$ it's my bowl". Smoke was pouring out of the door and I had to find the oven mitts to get the bowl out and soak it in water (so much for drying) Takes a very long time to get rid of that smell. I used Baking soda and everything. Would have set fire to the microwave if I hadn't reacted so quickly. That may be why I'm still single. Had to call my friend back and Lie about what happened, after all no ones that stupid.
 
I've used the MW a lot with some small pieces like someone else mentioned for pens and bottle stoppers. They seem to warp worse when MW'ed than just left to air dry, and it's not an instant thing. All you really are doing is heating the wood to make it dry faster.

After a major hurricane two summers ago (don't remember which one, we got hit with three that year) I wanted to make some pens out a special tree in a timely manner. I cut about 30 blanks, put 5 in the MW on a paper towel and nuked until hot but not hot enough to burn internally. Let them cool for an hour or so, rolled over 90 degrees, and nuked again. Repeated about 5 cycles over a few days and they were dry enough to turn for pens.

I dried the rest of them naturally in a month or so in a warm place with a small fan blowing on them. To be honest the ones that dried naturally seemed to have better grain and color, the nuked ones were rather dull looking but it may just be my imagination or othe factors.

I tried to dry a larger chuck for a turned box but it just checked and cracked badly. Not sure it is worth the trouble on anything other than pen blanks IMHO. :o
 
Longer times, lower settings, though the low settings are just interrupted full power. Real important not to have big thick spots here, because wood insulates pretty well, and the dry and well-insulated interior can ignite while the exterior is still held at 212F (100C) by evaporative cooling.

I've had some fun using vegetable bags. Clear plastic with lots of holes. Keeps things saturated around the piece while heating is being done, thereby limiting the temperature. Nuke, let cool to the dewpoint, then remove the plastic bag and turn it inside out. When the piece is cool to the touch, repeat.

Wood at the FSP is about 30% moisture by weight, so nuke about 20 to 25 out of it to keep yourself safe before you make your next decision. With all the heat (energy) inside, micro pieces are reverse gradient, with dryer inside.

You can also try some reforming, if you like. Relatively thin, a core somewhat smaller 2-5% than the piece, and handling the plasticized wood with gloves, put it over the form.

Woods with prominent rays would be the most likely to crack in the micro. Weaker spots to begin with. You can also run into problems with mineral stains on the outside. The extractives in the heart will come to the surface, and sometimes the random appearance isn't attractive.
 
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