Drying wood in microwave

[Rob Miller]

I rough-turned a green hickory bowl today and decided to try to dry it out in the microwave. I put it in for 30 seconds per cycle with enough time to completely cool between cycles. The oven was set at the quick defrost setting, which should be the lowest. The first and second cycles were fine, losing perhaps .10 to .20 ounces of moisture per cycle. On the third cycle I got cracks -- looks like checking, on the bottom curve of the bowl. I don't think there is a lower power setting than defrost, and the time doesn't seem excessive, particularly as the bowl is warm to the touch but not really hot when I remove it. Am I doing something wrong?

[Ralph Boumenot]

Doesn't sound like to me that you are not allowing the wood to relax after giving up it's moisture. The cells are shrinking too fast and you're getting cracks.

[Fred Belknap]

Rob I have successfully dried some pieces in the microwave. I put the piece in a plastic bag and put it in the microwave on high power for two minutes. Take out of the bag and let cool for five minutes. Then turn the plastic bag inside out and put the bowl back in for two more minutes. I usually check the weight every other cycle. In the cooling part the piece needs to be covered with something to keep it from cooling down to fast, I use an old insulated coat. The point is to keep the piece hot and wet. Caution, you will need gloves because it gets to hot to handle. It works but it takes quite a while to get something dry and you have to stay with it. It is kind of hard to tell when it is dry enough because it is still wet. Don't let it cool down to quick, then check the weight for the next couple days or so to see if it is really dry. I have had some pieces actually gain weight after using this process. I only use this process if I really need something dried quick. It isn't 100%, I have had a few that cracked which possibly was my fault or maybe a fault in the wood.

[Jeff Gilfor]

I regularly microwave green blanks after rough turning.

I use a 1200 watt oven. Piece in for 30 minutes at 20% power. Let stand for several hours and repeat as needed, but no more than 3 cycles. If still not dry enough, I let it air dry the rest of the way.

Problem with programmed defrost cycles, is that most ovens go high for some portion if the cycle. I guarantee that anything higher than 20% will dramatically increase chance if cracking.

You do not want the water to boil! You simply want it heated to greater than 125 degrees or so but less than 200.

[Rob Miller]

I regularly microwave green blanks after rough turning.

I use a 1200 watt oven. Piece in for 30 minutes at 20% power. Let stand for several hours and repeat as needed, but no more than 3 cycles. If still not dry enough, I let it air dry the rest of the way.

Problem with programmed defrost cycles, is that most ovens go high for some portion if the cycle. I guarantee that anything higher than 20% will dramatically increase chance if cracking.

You do not want the water to boil! You simply want it heated to greater than 125 degrees or so but less than 200.

30 minutes? that sounds like a really long time. I didn't let the entire defrost cycle run -- it would have run for 3 minutes, but I took it out after 30 seconds. Also, I left the piece in a bag overnight and when I checked it this morning, the cracks had closed back up, which I found sort of interesting. Do you think I'll have better luck with this method, or with boiling?

[Jeff Gilfor]

I've never done the boiling thing. No place in my shop to do that, and my wife would shoot me if I used the kitchen.

I haven't had any probs with 20% for up to an hour. I do 30 minute cycles because I have found no need for longer. I prefer more cycles over longer cooking time.

Yes, 30 minutes us longer than what you hear others quote, but I have had great results with all wood species using this method. I also do not cover or bag the pieces while doing this or allowing to equillibrate to room temp.

Understand that I am in Tampa. And my shop is a converted air conditioned garage. I do turn the AC off when I am not there though. The ambient temp varies from 74 to 105 degrees, depending in outside weather. RH may be anywhere between 30 and 100%.

[Rob Miller]

I'm in Arizona, Jeff -- the RH is a bit different here, :cool: although I'm not sure how that will affect the process. I ran the last cycle for 5 minutes at power level 1 and it really sweated out quite a bit of moisture with less apparent movement. The cracks have all disappeared. Hopefully they'll stay tight.

[John Keeton]

Sounds like everyone has a different method - not unusual in the world of woodturning! I rough to about 1/2" and nuke at high power for very short cycles - 30 sec to a minute. I don't use a bag, just remove the piece and let it cool to a warm temp and repeat.

[Harry Robinette]

Somewhere ether in one of his books, or on the net somewhere Micheal Hosilick (spelling) has or had a micro waveing how to.He does allot of his work with a microwave. I'll try to find it when I get some time.