Microwave Drying of Turned Wood
by WNT member Dewayne Hines

This article deals with one of the most frustrating things that beginning woodturners encounter - cracking wood. You put a piece of wood on the lathe and turn a nice bowl then several days later it starts to crack and sometimes you end up with a two piece bowl. Well, there is good news and bad news. The good news is that there are solutions to the cracking problem that work very well. The bad news is that there is no panacea and no instant fixes.

There is one thing that will help reduce cracking tendencies in any piece and that is to turn a uniform thickness. This is true whether you do a two step process (rough turn, let the wood dry and then finish turn) or you turn green wood to finish form. It is not possible with some designs to have a uniform thickness but when you can, it will help the wood dry more evenly.

When I first started turning 5 years ago I had a lot to learn. One of the first things was that green wood is much easier to turn than dry wood. And you can find thicker pieces of green wood for bowls. Another thing I learned is that when you ask experienced wood turners for advice -- you get advice. The advice I got for using green wood was to turn the bowls 1 inch thick, place them in paper bags for a year to let them air dry and then turn them to the final thickness. I was told to expect a forty percent failure rate while drying due to cracking and warping.

I didn’t want to wait a year so I started looking for information and found a couple items on the Internet that mentioned using a microwave oven to dry the wood quickly. I tried it and was pleased with the results. I have made dozens of bowls and dried them all successfully in the microwave. The bowls still warp and crack, but because it is done in stages, the cracks are glued up when they first start. Warped bowls are viewed by many people to be artistic.

Start by turning green or partially dried wood into a bowl shape. Once you are satisfied with the shape, cut the sides of the bowl to desired thickness. I prefer a thickness of one-eighth to one-quarter inch. Sand the bowl to 220 grit. If the wood is extremely wet, it may be better to sand it after drying. The foot on the base of the bowl can be left on to allow sanding after drying. If the bowl will be left unattended for more than an hour during the turning process cover it with a plastic bag to prevent cracking. Any cracks that occur during turning can be filled with CA glue and sawdust.

Microwave Drying Procedure:

1. Cover the bowl with paper towels and a dishtowel and place in a plastic grocery bag.
2. Tie the bag loosely to let air escape and place in the microwave.
3. Set the microwave oven to low power. (Level 1 or 2 out of 10)
4. Set the timer for 2 minutes.
5. Start the oven.
6. When the microwave stops let the bowl sit in the bag in the oven for 10 minutes.
7. Take the bowl out and unwrap it. The bag and the towels will be wet.
8. Let the bowl sit uncovered for 20 minutes. Check it for cracks – glue up if needed.
9. Rewrap with dry towels and continue drying until there is no water on the bag.
10. Large bowls (up to 14 inches) take 6-8 turns. Small bowls 4-5.

You can spread out the drying over several days by drying a turn or two each day and then covering the bowl with towels and plastic to wait till the next day.

Several points of caution need to be added. First, do not leave wood unattended in the microwave. Also, be careful with the timer because touch pad devices can develop erratic problems like jumping from 2:00 minutes to 20:00 minutes! Finally, after you remove the wood from the microwave it should be watched at least 30 minutes for signs of internal combustion. Microwaves heat from the inside and overheating can start the wood to burn inside. This should not be a problem at the power levels and times described here, but it never hurts to err on the side of caution. It is also a good idea to keep a fire extinguisher handy.

If you want to investigate other articles on micro waving wood, check out Steve Worcester’s website http://www.turningwood.com and click on "How to Articles". If you have a drying method that you have found effective please share it with other WNT members. Write an article and send it to either Bill Boehme or Paul Tiefel.