Microwave drying small pieces of wood

[Dave Mount]

This isn't about turning per se, but because most of the expertise in microwave drying seems to come from turners, I'm hoping the moderators leave the question here.

In a hurry to apply some knife scales to a knife blank for a Christmas present. Recently acquired some bocote, and it seems aesthetically like the perfect wood, but it is not dry. Doesn't seem sopping wet, but I turned a small sphere from it (see, there's some turning content!) and when I brought the sphere into the house, it checked (we're well into wood heating season here in northern MN, low RH in the house).

I did a bunch of searching on microwave drying and while there's a lot of discussion about it, there's a lot of conflicting advice (e.g., barely warm the wood vs. wood will be too hot to touch when it comes out of the microwave, bag vs. don't bag).

This will be two pieces of wood, 3/8" thick, about 1.25" by 5". My microwave goes clear down to 10% power, and it's a real 10% (constant low power, instead of 5 seconds on full and 45 seconds off, as our previous microwave was). It seems clear I only want to use 10 or 20% power. Anybody care to offer suggestions on how much to warm them? I'm thinking in terms of temperature rather than time -- I have an IR gun so I should be able to monitor temp fairly well and since it's the mass of the pieces that matters (I presume) I'm thinking temp is the better measure than time. I also know that I may have to experiment, but the bocote is pricey stuff, I'm not anxious to waste it unnecessarily.

Thanks for any pointers.

Best,

Dave

[John K Jordan]

Dave, it's been years since I've done any microwave drying. It worked well but was time consuming. The problem, as you suspected, is finding the right balance. Heat the wood just a bit too long and it might start burning inside. And if you dry too fast wet wood is likely to crack.

I did small turning blanks, maybe 1" square, heated for just a short time until the wood was slightly warm to the touch. Took it out of the microwave oven and let the wood cool completely - it will be casting off water vapor. Repeat. Weigh the wood with a gram scale and when the weight quits changing it is dry. At this point it may be drier than you want, well below EMC but that's a lot better than it being too wet. Before use, I would let small pieces like yours acclimate indoors for a few days before use.

When I used the process it took many cycles over the course of 1/2 a day, erring on the side of caution over haste. I have a microwave oven in the shop - setting fire to wood in the kitchen microwave might make the chief chef unhappy.

BTW, the reason I don't use microwave drying any more is not because it didn't work, but because I now have a huge stock of dry wood, some has been air drying for well over a decade and I have no reason to hurry.

JKJ



This isn't about turning per se, but because most of the expertise in microwave drying seems to come from turners, I'm hoping the moderators leave the question here.

In a hurry to apply some knife scales to a knife blank for a Christmas present. Recently acquired some bocote, and it seems aesthetically like the perfect wood, but it is not dry. Doesn't seem sopping wet, but I turned a small sphere from it (see, there's some turning content!) and when I brought the sphere into the house, it checked (we're well into wood heating season here in northern MN, low RH in the house).

I did a bunch of searching on microwave drying and while there's a lot of discussion about it, there's a lot of conflicting advice (e.g., barely warm the wood vs. wood will be too hot to touch when it comes out of the microwave, bag vs. don't bag).

This will be two pieces of wood, 3/8" thick, about 1.25" by 5". My microwave goes clear down to 10% power, and it's a real 10% (constant low power, instead of 5 seconds on full and 45 seconds off, as our previous microwave was). It seems clear I only want to use 10 or 20% power. Anybody care to offer suggestions on how much to warm them? I'm thinking in terms of temperature rather than time -- I have an IR gun so I should be able to monitor temp fairly well and since it's the mass of the pieces that matters (I presume) I'm thinking temp is the better measure than time. I also know that I may have to experiment, but the bocote is pricey stuff, I'm not anxious to waste it unnecessarily.

Thanks for any pointers.

Best,

Dave

[Barry McFadden]

I do pretty much the same as John does. I would put the wood in at 40% for about 2 minutes. sometimes up to 4 minutes then let it cool for a while and weigh it after each time and keep doing it until the weight doesn't change. Never had a piece get too hot or burn....

[Bert Kemp]

I tried this once and had to toss the Microwave as it really stunk up the house afterwards .

[Alex Zeller]

I've done it several times. My microwave doesn't really have a power setting (most don't). It just turns the microwave on and off. What I did was start off at a short time, heated the blank up, took it out, and let it cool for a few minutes and checked the weight compared to what it weighed before going into the microwave. Repeat until the weight seams to stabilize. I had better luck doing it with wood that was partially dry, maybe 25%. Stuff that's really wet always seamed to crack. With something that small you could seal the end grain and put it in your oven on the lowest setting. Or the alcohol trick may work better.