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Using a microwave kiln to dry wood

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Forum topic by MatThreet posted 01-19-2021 02:03 PM 228 views 0 times favorited 2 replies Add to Favorites Watch
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MatThreet

1 post in 38 days


01-19-2021 02:03 PM

Topic tags/keywords: kiln drying

Newbie here so thank you for taking the time to read this post. My grandfather is a wood worker and is interested in building his own kiln for drying wood. He and his partner have a general idea on how this works but he is looking for someone who’s ear he can bend with some questions. He does not really use the internet much.

I know his main questions are concerning the use of microwaves as a heating source ( I may not be explaining this correctly). I’m not sure if this is an appropriate place to ask. I am just reaching out as a favor to him. Would anyone like to take some time to answer some questions?

Thank you either way.


2 replies so far

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Lazyman

6618 posts in 2392 days


#1 posted 01-19-2021 02:28 PM

I use a microwave oven to dry green bowl blanks after rough turning them on my lathe but if you are talking about taking the microwave element out of a microwave oven to make a kiln for drying boards or lumber, I don’t think that is something the average person could do safely. It is sort of a “if you have to ask, then don’t” situation. If the wood he wants to dry will fit into a microwave oven, then it is definitely doable.

Here is my basic process for the bowl blanks in a microwave oven in case that is what he is trying to do. I’ve done very small blocks of wood this way too. I generally rough turn the bowl so that the thickness is 10% of bowl diameter before starting the drying process.
  1. Weigh and record the weight of rough bowl. I use a digital kitchen scale.
  2. Heat the bowl at 30-50% power for 2-3 minutes. The bigger and wetter the wood the higher power and the longer you can heat it. When starting out, err on the side of shorter and lower power until you get a feel for how much heat a piece of wood can take. If it is too hot to touch or you smell burning, you heated too high and/or too long.
  3. Remove the bowl from the oven and let it cool down
  4. After it is cool, weigh and record the weight
  5. Repeat all previous steps until it stops losing weight. As you notice the weight change between cycles is declining, lower the power and shorten the time to prevent charring the wood.
  6. I usually wait overnight and do one more short cycle after the last one to see if it loses any more weight.

Once it is dry, I turn to final thickness and shape.

If drying a few boards is what he wants to do then I would build an insulated hot box and use a halogen light bulb as the heat source with a thermostat to set a target temperature. You need air intake and exhaust and may want to add a fan if convection doesn’t adequately remove the humid air. I’ve also seen people use defunct refrigerators to do this instead of building a hot box.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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Rich1955

313 posts in 395 days


#2 posted 01-19-2021 02:39 PM

I can’t answer your question but I was listening to the Fine Woodworking podcast and Ben Strano who works for the Fine Woodworking magazine has one that uses a light bulb as a heat source and a thermostat. You can contact him at Taunton.com. These guys answer questions all the time and can be very helpful.

-- Rich

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