Microwave Drying

[LANKFORD]

Old stuff I am sure. I have read lots about microwave drying, but it seems everyone talks about turning bowls to say 1/2" wall then sticking in an oven. I am doing mostly small boxes and bowls like Ms Kline does. I got interested through her tapes. What I want to do is dry blocks before turning, about 2 or 3" square and no more than 4 to 6" long; that size of chunk. If I dry 1 at a time or say 6 blocks at once, what kind of time does this take for green wood and is there any difference in the heat setting and time for 1 or 6?

 

[Bill Boehme]

I know that it sounds like an oxymoron, but microwave drying needs to be done slowly for good results. I think that most people who try it rush things too much and cause as much damage as sticking something out in the hot summer sun to dry. I would like to suggest the following link to microwave drying on the Woodturners of North Texas web site as a general guideline that you could use. Using the method described in the article, I have dried finished turned freshly cut green wood without any ill effects except for very minor warping. Obviously, this would not work on turned boxes so an adaptation for blanks could probably be done -- it would just take longer and please don't give in to the temptation to rush things by running the power up.

Bill

 

[John Abt]

Microwaving Blanks

I use a microwave to dry bowls. I was planning to start on some square blanks for some spindle turning soon.

I think the key is to keep a log of the weight of a given piece and/or use a moisture meter (a cheap one runs about $20 at Harbor Freight).

Using the weighing method, I suggest writing an identification of some sort on each blank (since you want to dry more than one). Using a kitchen scale (I use an inexpensive digital scale set to grams because it makes the math much easier :cool2: )

I use a 1200 watt microwave with turntable. I set the power to 3 and "cokk" the pieces for 2 minutes. Take each piece out and reweigh it. It probably has not lost much. if any. You can leave the pieces out (I do) to cool for at least 30 minutes. This lets the moisture wick off. Reweigh the pieces and microwave again. I found out the hard way that if the piece is hot (or even warm) DON'T reheat it. Let it sit.

John

 

[Frank Kobilsek]

Bag'em

Lankford
I dry blanks for bottle stoppers in the microwave. Cut balnks to size. Put 12 to 15 in a grocery bag (paper). Nuke for 2 to 3 minutes on defrost. Remove from oven and give them a good mixing in the bag. I repeat this cycle 2 to 4 times per day for about a week. At least 15 to 20 cycles. Then leave them in the bag for another week to rest. Then they are ready to turn.

I don't have a moisture meter or scale. You'll notice how hot they get when they are wet. When they are dry they don't get that warm. Not very scientific but it works for me.
Frank

 

[cweddig]

First Post and very glad to be here. I was taught by a man who used microwaving already turned stock, again it was turned thin. I have used the microwave process to alter/warp the shape into a one I couldn't turn. I find this desireable, some do not. I am curious to try this on a blank. I thought this would take a long time. Thanks for the perspective.

Chris

 

[MichaelMouse]

I dry blanks for bottle stoppers in the microwave. Cut balnks to size. Put 12 to 15 in a grocery bag (paper).

Careful with the bagging business. You'll see a warning in the manual of most machines about nuking printed paper. Not sure if it's lawyer sidestep or actual fire that makes them put it there. Theory favors lawyer.

Blocks are a problem, because wood doesn't lose moisture at the same rate through the sides as it does from the ends. On the sides water has to go through the stomata in the cell walls and travel sort of at random through the various levels of cells before finally escaping to the surface. Means it more or less obeys the inverse square rule which says four times to travel a half inch as it takes for a quarter. Since it could also exit a cell into a vessel and sprint out on occasion, the actual seems to be three times as long according to the wood techs.

All of which means that the moisture taking the easy way out through the "predrilled" end grain rushes through and makes dry spots inside the well-insulated center of the block while the other is still working its way sideways. Dry spots ignite.

TDT (Turn Dry Turn) is still the best way to go. Of course, your suction-fit box lid will fit perfectly only briefly, because you may still be wet or may have gone too dry for conditions, but you'll love it until you show it to your wife a couple hours later and it sticks.

If you go the TDT route, check the tables at the FPL or Hoadley to get the average shrinkage for your species of wood, add a fudge for comfort, and nuke slow and longer. This will help prevent hot spots from differential drying, and will reduce the amount of harder dry wood you have to remove when you re-mount, which you will also have to allow for, and turn to final.

 

[john lucas]

I have dried bowls, and small pieces of wood but never box blanks. I rough turn the boxes and then dry them in the microwave. Then I final turn the boxes. If you decide to dry whole blanks for boxes dry them slowly. I have dried christmas ornament sized blocks. I put them in the oven for 30 seconds and then go do something else. I'll do this off and on all day, whenever I happen by the microwave. It take s 10 to 15 cycles to be completely dry. I have a triple beam scale setting next to my microwave. Everyone thinks I'm on some kind of diet when they see the scales.

 

[john lucas]

Oh I forgot to say don't heat them too much. It takes forever for the smell of burning wood to get out of the microwave. I only know because my "friend" did this. It wasn't me honest.