Drying Box

[Don Frank]

tom,
Try it first without a fan. Fill it up, as much stuff that you can pack in there, shut the door and keep the temp under 100. As long as you have some venting at the top you should get good results. Stuff starts cracking with a fan. I have two dishwasher kilns and they are self venting so i didn't have to do anything else. The trick for mine is to not open the door for at least three weeks. The other trick is to do as many pieces as possible. The humidity builds up and controls the heat somewhat and gradually dissipates as long as you don't open the door. The bottom of mine are not sealed tight where the motor was removed, just a reflector setting in the hole. I'm sure this allows some air to flow from the bottom and up thru the vents. They work good.

[Reed Gray]

Any type of box can work. What the light bulb does is set up convection flow, as in hot air rises. So, you will need an opening in the bottom for the light bulb, and an opening in the top/chimney so the air can escape. If you live in a very cold climate, like way below freezing, then insulating the box might be a big help. The taller the box, the more flow you will get, as well as the bigger the bulb you use, the more flow you will get. I do almost totally, once turned bowls, Here in the damp Pacific NW, even in the winter, they are dry and stop warping in about a week. As far as I am concerned, no need to speed dry them. Do wrap the edges with stretch film as that is the most vulnerable area for cracks to start. You could build a plywood box with stainless screen shelves and put a lot of bowls in it. I wouldn't use anything more than a 20 or so watt bulb. Dry too fast and you get cracks. Dry too slow and you get mold.

robo hippy

[Malcolm McLeod]

For the USA incandescent bulb users, you might want to check what happens in Aug '23.

[Maurice Mcmurry]

Yes, they are going the way of the Easy Bake Oven and the Fuller Brush Man. I will stock up. There are alternatives.
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[tom lucas]

Completed the project today. Used 1.5" foam insulation to make a "hat" that fits around the cabinet. Cabinet just sits on the bottom insulation, and the 4-sided hat drops down tightly over the cabinet. Removes with no disassembly. I put 9 3/8" holes in the top, and 4 holes in the bottom, plus 2 for the lamp holders. I used double ended lamp holders to give me greatest flexibility. To start with 2 25W bulbs installed in opposite directions and 2 outlet adapters in the other lamp sockets. If I need a fan, I can just plug it in.

At vent holes I over sized the insulation around them to accept 1" ID PVC pipe, mainly to protect the holes in the foam without having to be too precise with alignment. I set the controller to 100 degrees. It took 4 hours to reach temperature with no load and all vents open. The temperature was around a cool 50 degrees in my shop at the start. Shop was probably 65 degrees 4 hours later. Don't know if the heat-up time is slow, fast, or just right. Pics below

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[Maurice Mcmurry]

That is deluxe! Nicely done! The glass door is going to be a really nice feature. Now to find a good place for it to live.

[tom lucas]

That is deluxe! Nicely done! The glass door is going to be a really nice feature. Now to find a good place for it to live.

Thanks for the compliment. It has been moved to it's new home: on top of the dorm fridge in the back room using space heretofore unused. It's not a big kiln, but it doesn't take much space and it's all I think I need.

[Dave Mount]

Sorry to be late to this thread, but the important parameter to monitor when drying wood is not temperature, it is relative humidity.

Raising temperature alone decreases relative humidity, and that alone will encourage cracking if steps are not taken to keep relative humidity at appropriate levels. Commercial kiln schedules commonly start at 180 F, but also at 80% RH. The issue is to get the moisture from the interior of the wood to the outside where it can evaporate, but to limit surface evaporation to a rate that the outside does not shrink (dry) too fast around the swollen interior and cause checking. Heat speeds the migration of moisture within wood, but RH is important in controlling how fast it evaporates (temp has an influence too, but RH dominates).

With regard to the ventilation of the cabinet, RH is how to determine appropriate airflow. How fast you can push drying is dependent on the species, but generally speaking dead green wood will dry fastest (without cracking) at high temp (up to and including 180 F, as noted above) but at high RH. RH is dropped after much of the initial water is lost. Cheap but surprisingly accurate digital hygrometers (humidity meters) can be used to monitor RH. Make the chamber as warm as you wish/can, but regulate air exchange to maintain RH in the 80% range initially, then drop the RH as the wood approaches dry. Google wood kiln drying schedules and you'll get all kinds of quantitative info on the process. The high tech approach is to use a small fan to ventilate the cabinet and hook it to a humidistat so that the fan is activated when RH in the cabinet rises above the selected RH.

You can figure out where the wood in the cabinet is in the drying process by sealing the cabinet for a couple days and seeing where RH settles without airflow.

Here's an example of the inexpensive hygrometers you can buy: https://www.amazon.com/TASOGEN-Therm.../dp/B08P3QJJZL

I use them all the time for assessing moisture content of wood, mostly turning blanks of uncertain seasoning. The relationship between RH and wood moisture is discussed here: https://www.wood-database.com/wood-and-moisture/

Best,

Dave

[tom lucas]

Thanks David,

This info will be very helpful going forward. I ordered some hygrometers. Nonetheless, I already have 8 bowls in there since last Sunday morning. They are a mix of nearly dry cherry and some half dry apple. The apple bowls were packed with shavings from same with the outside rims wrapped in plastic. All are about 8" dia and 3/4" thick. The first day, the chamber glass door was covered in condensation (using in a very cold shop), temp was about 80 degrees. By the 2nd day the condensation was gone. Fourth day I closed off some of the vents (from 9 to 5) and raised the temperature to 90. That's where they've been since. So far no signs of cracks. Plan to weigh again on Saturday morning. Next batch I'll develop a more rigorous temp/humidity profile to follow.