Microwave drying

[WH Seelinger]

I know that there have been many threads on Microwave drying of wood, but I tried something earlier in the week that might be helpful.

Started with a rough turned maple bowl, around 13" in dia, left it 1"+ in thickness. it weighted 4lbs 14 oz. Ended up drying it 14 times, it came out 4 lbs. I did let the piece cool to below 80 degrees before the next cycle.

The first cycle was for 5 minutes, I took an infrared thermometer and checked inside and outside of the piece after it finished. 120 degrees F was the highest spot. Microwaving basically boils the moisture out of the wood, so I bumped up the next four runs to 6 minutes. The next three cycles topped out at 180 degrees, the fourth came out at 200 degrees. The next four cycles were at 5 minutes, max temperature went from 180 to 190 on the last cycle. Each cycle, the piece lost an ounce and a half of weight. I did one more 5 minute cycle, and found the bottom of the piece was at 265 degrees.
It had only lost 1/2 ounce.

I did a 3 minute cycle, 180 degrees max and lost .5 oz. 2 more runs at three minutes showed the temperature the same, and .5 oz loss. The final cycle showed the temperature about half way up the piece at 240 degrees, it only lost .2 oz.

I am thinking that there is merit to checking temperature while drying and that 180-190 degrees would be a good point to judge the time of cycle.

WH

 

[John Torchick]

Is the cycle a defrost cycle What setting did you use? Thanks. Found I can get a MWO much cheaper than a dehydrator.

 

[WH Seelinger]

Is the cycle a defrost cycle What setting did you use? Thanks. Found I can get a MWO much cheaper than a dehydrator.

I am calling a cycle, one session in the Microwave. I use the high setting for temperature, the time in the oven is kind of a guess, using the infrared thermometer seems to me, to be a way to see what is happening to the wood to optimize the time.

When I first started drying wood in the Microwave, I left a piece of walnut in too long and set it on fire internally, no flame, but a lot of smoke. Took it outside and it would not quit smoking. I had to dunk it in water.

If you try using this method, read everything you can, go slow, and keep a log of the time and temperature.

 

[Scott Hargrove]

I've done the same with good success ... 5 minutes on high for a medium to large bowl blank, weighing before and after microwaving, and checking with a moisture meter once it gets fairly dry. I've done five minutes at a time until the piece comes out without a lot of steam, and then start backing off the time. I've never had a piece burn at all. I hadn't thought of the infrared thermometer. I think that's a great idea, because it takes out a lot of the guesswork.
I've read about people using low heat for a minute at a time, and that just seemed way to slow and probably completely ineffective. I think your post proves that.
Again, the thermometer seems to be a great idea.

 

[Paul Paukstelis]

I've read about people using low heat for a minute at a time, and that just seemed way to slow and probably completely ineffective. I think your post proves that.
Again, the thermometer seems to be a great idea.

I did quite a bit of experimenting quite a while back and I found the best way to maintain a constant internal and external is to do an initial longer cycle (4 to 6 minutes depending on mass and moisture content) followed by a roughly 10% duty cycle, usually 1 minute on, 10 minutes off (with fan going). Of course, this would be a pain to do manually so I added a Esp-32 microcontroller to run the microwave keypad, letting me set cycle parameters via wifi. Works great, but I almost never use it, so if anyone wants it....

 

[Scott Hargrove]

I did quite a bit of experimenting quite a while back and I found the best way to maintain a constant internal and external is to do an initial longer cycle (4 to 6 minutes depending on mass and moisture content) followed by a roughly 10% duty cycle, usually 1 minute on, 10 minutes off (with fan going). Of course, this would be a pain to do manually so I added a Esp-32 microcontroller to run the microwave keypad, letting me set cycle parameters via wifi. Works great, but I almost never use it, so if anyone wants it....

I guess I'm not techie enough know what an esp-32 is, but being able to control by wifi would be great.

 

[Dennis J Gooding]

For what it is worth, note that the IR thermometer will report the surface temperature of the piece, not the internal temperature.

 

[WH Seelinger]

For what it is worth, note that the IR thermometer will report the surface temperature of the piece, not the internal temperature.

I understand we are talking surface temp. If we took a pan of boiling water and checked it with an IR thermometer, it should read 212 degrees, when the water boils off, the temp will rise.

 

[Kent Reisdorph]

so I added a Esp-32 microcontroller to run the microwave keypad, letting me set cycle parameters via wifi. Works great, but I almost never use it, so if anyone wants it....

Of course you did.

 

[Darryl Fective]

Is the cycle a defrost cycle What setting did you use? Thanks. Found I can get a MWO much cheaper than a dehydrator.

I got one for free off Facebook Marketplace.

This is very interesting. I also have the impatience bug, but haven't tried any extended times, just 30 second blasts. I haven't checked temps other than by feel. I don't always let it cool completely before the next round, either. If only I took notes... I've also been experimenting with a soaking roughed blanks in denatured alcohol first.