Building a humidity controlled drying box for fine woods

Greenberg Woods

Greenberg Woods

Joined
Dec 27, 2013
Messages
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Hey guys. I recently got a big pile of birdseye figured black and white ebony in from Laos, and they are nearly completely green. So i figured it was time to set up a drying apparatus.

The physics of safely drying wood are, to put it simply, complicated. Its not as simple as saying a kiln dries wood more safely than air, or that high heat is more dangerous for wood than low humidity, its complicated. Im using a mix of sources, but the work by Gene Wengert is invaluable. https://www.wagnermeters.com/moisture-meters/wood-moisture-training/wood-doctor-videos/
http://www.lignomatusa.com/wp-content/uploads/2015/02/DryingLumber.pdf

I dont pay for power at my workshop, so i will be using a closed system removing all the water with a dehumidifier. This will be more power intensive, but should give me more control.

I will only post the rough outline of my plans on bladeforums, since i would hate to accidentally mention that i sell wood and get accused of ruining this forum again, so if you want to keep track of this project in a more detailed way, or to see my measurements, laser cut files, or the data i collect for safe drying rates of exotic woods through a series of tests, all of that information will be on my website.

Put simply, i will be using a converted 72 x 48 x 18 inch cabinet with a set of fans, heaters and a dehumidifider controlled by a PID humidistat. By keeping the system sealed instead of using a constant inflow and outflow, i should be able to better measure the rate of moisture loss, as I can weigh the mass of the water removed against the weight of wood i started with to calculate the % of moisture it represents.

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And here is what will be going in the kiln for its first runs

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Ouch. Good luck,be careful! Maybe silicone caulk all metal corners and seams, and put some kind of gasket around the door? Humidistat can be touchy - fwiw I recommend getting a really good one to keep things accurate
 
Takes balls to start with B&W ebony. Thats the hardest wood to dry without cracking that I have messed with. SLOW
 
Ben not sure if you are aware but if you have questions you can ask Mr. Wengert directly on the sawing and drying forum at woodweb.com
 
Ben, I like the basic idea. I used the exact same cabinet to dry wood with a 75 watt bulb in the bottom. It worked quite well. It is full of electrical parts and motors right now, but I may put it back in use if I decide to get back into drying wood.

One issue with your weight calculation plan is it won't tell you what the moisture level in any one piece of wood is. It will tell you how much moisture has been removed as a whole. For an extreme example, If you put in fresh cut buckeye burl in along with desert ironwood, the buckeye burl will give up most all the water you recover.
 
Stacy E. Apelt - Bladesmith said:
Ben, I like the basic idea. I used the exact same cabinet to dry wood with a 75 watt bulb in the bottom. It worked quite well. It is full of electrical parts and motors right now, but I may put it back in use if I decide to get back into drying wood.

One issue with your weight calculation plan is it won't tell you what the moisture level in any one piece of wood is. It will tell you how much moisture has been removed as a whole. For an extreme example, If you put in fresh cut buckeye burl in along with desert ironwood, the buckeye burl will give up most all the water you recover.
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Yeah, ill have to do species specific runs. I actually don't see it being too huge of a problem, I have about 200 pounds of Birdseye ebony from one tree, a few hundred pounds of wet walnut burls, the woods that need special drying i gave in decent enough bulk that I can run species specific runs.
 
Yes, I figured you would do single species batches , which in your level is a large amount. This looks like a fun project for you. Can't wait to see the results.

My second concern was that the dehumidifier might draw the moisture too fast. Any thoughts about that?
 
i am guessing you are trying to dry the wood, while keeping the moisture content consistent throughout the piece, because if its more dry on the outside than the inside it will warp ? maybe you could put the light bulb on a dimmer or thermostat to control the temp more precisely.
 
Stacy E. Apelt - Bladesmith said:
Yes, I figured you would do single species batches , which in your level is a large amount. This looks like a fun project for you. Can't wait to see the results.

My second concern was that the dehumidifier might draw the moisture too fast. Any thoughts about that?
Click to expand...

I bought a pretty sensitive humidistat which will duty cycle it on and off. with strong turbulent airflow, the worst i can imagine happening is that it runs in a lot of small bursts, which while not the best for efficiency, in my particular set up is not that big of a deal.
 
john april said:
i am guessing you are trying to dry the wood, while keeping the moisture content consistent throughout the piece, because if its more dry on the outside than the inside it will warp ? maybe you could put the light bulb on a dimmer or thermostat to control the temp more precisely.
Click to expand...

The moisture content from the inside to the outside will always have a gradient, the key is to do it slowly enough and evenly enough that the stress built up in the first stage of drying can be safely released in the second stage when the inner areas lost more water.

I plan to do this at a lower temp than normal, as wood is stronger at lower temps and less likely to crack. As for heat generated, the dehumidifer may even released too much heat between both the inefficacies of heat pump action, as well as the enthalpy of formation released by the water as it condenses. If the generated heat is too great, i will need to great i will need to lay some ducting to have the dehumidifier in a separate area with the air circulating through and cool the dehumidifiers area with a cross breeze.
 
Ben - how can you identify how fast (drying wise) is too fast, without waiting to see cracks ... and then it is too late?
 
Cushing H. said:
Ben - how can you identify how fast (drying wise) is too fast, without waiting to see cracks ... and then it is too late?
Click to expand...

There are drying rates of moisture loss% per day for many woods, im basing mine on that information and starting with cut offs of the same species
 
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