Drying Box

[tom lucas]

I have this stainless steel enclosure with glass back and glass door. It's about 20 x 16 x 20 deep. A scientific drying rack, I'm guessing was its originally use. No holes in it. Has 2 mesh shelves and one solid one. Plan to modify it for a dryer. Will probably hold 6 large bowls at a time. Likely pretty air tight. Those who have done it, any advice you could lend to how best to heat would be appreciated.

Should I insulate it?
Best spot for bulb?
Bulb type/wattage to use?
Fan needed? Vented or just circulate? Placement relative to bulb?

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[Maurice Mcmurry]

What heat range are you hoping for? I use incandescent light bulbs. It only takes a few watts if you add insulation. Thats going to be excellent.

[Kevin Jenness]

Depends what you are trying to do. Speeding up the drying of rough-turned vessels can backfire depending on species, thickness, initial moisture content, etc. I usually try to slow it down with Anchor Seal, keeping the pieces in a moderate heat/humidity/low air flow environment, sometimes inside a paper bag or cardboard box, at least during the initial drying stages from green. Once-turned pieces usually dry out pretty fast without encouragement.

If you are intent on doing this, insulate the box, monitor the conditions and add controlled venting if needed. A low voltage incandescent bulb should suffice.

A former neighbor who turned epoxy "enhanced" burls had a similar chamber for his roughouts but in his case drying induced cracks were a feature.

[tom lucas]

Was thinking to use for both rough cut blanks as well as once-turned things. Purpose is to speed up drying without cracking. Thinking I'd have the option to adjust the heat either by using 1 or 2 bulbs at the same time, or by using a dimmer. To keep the bulbs small, was wondering about T10/T30 footprints installed in right angle sockets. Maybe one on each side for even heating. Wattage may be the biggest question.

[Kevin Jenness]

A small fan would probably be a good idea, perhaps a computer muffin fan. If the box is insulated I suspect overheating is the main hazard, so monitor and adjust the temp and rh.

[Maurice Mcmurry]

experimenting is your friend. The weak link with mine it temperature monitoring. My next need is for two thermometers one for the cabinet interior, and one for the center of the wood. I want a way to check both without having to open the door. I currently have 4 53 watt (75 replacement) regular bulbs. I only use all four for making red neck ebony. My bulb holders sit on the bottom above good size holes for the wire's and to let air in. There is a vent at the top. The convection creates good air flow. It is also very handy for killing bugs and speeding up glue & paint.

[Richard Coers]

Most importantly, you want the box ventilated at first. 6 wet bowls or blanks will flash over with mold in a warm moist enclosed space
Should I insulate it? Yes
Best spot for bulb? Heat rises, bulb on the bottom
Bulb type/wattage to use? Heavy service duty incandescent. I use a cheap hot plate in mine for an adjustable heat.
Fan needed? Vented or just circulate? Placement relative to bulb? Fan placement makes no difference.

[tom lucas]

What is the temperature setting most try to maintain?

[Maurice Mcmurry]

For green wood I start at 90 and slowly work up to 140.

[Wally Crawford]

My drying box is made from an old fridge. I use varying wattages of incandescent bulbs to maintain 100*. There are two 3" holes cut into the interior of the fridge, one low and one high for a natural chimney effect. Temps are monitored with two remote sensing thermometers from Amazon.

[Brice Rogers]

You said: " No holes in it. ... Likely pretty air tight."

So, if you want it to be a dryer, you've got to modify it. No hole, air tight? Sounds like a Mason fruit jar or a thermos.

[tom lucas]

On further inspection the case is very air tight, front door has a heavy rubber gasket. My plan right now is to use two 25W T10/T30 bulbs, one on each side in the bottom, mounted tight along the side bottom corners. The sockets I've chose each support two bulbs. So I could put 4 bulbs in there at whatever wattage is best, if needed. The box is about 2/3 the size of a dorm fridge. So, not real big.

I plan to drill 6 small (1/2 inch) holes in the bottom and 12 (3/8 in) in the top. The top holes will be 3 rows of 4 holes, back- middle - front. A temperature controller will control on/off. Not sure on fan placement. I might leave it on hooks that can hang from anywhere on the racks. If the fan gets permanently mounted, was thinking top facing down maybe??? The bottom shelf is solid stainless, and I'll have to drill several holes in it for air flow on that shelf.

The whole thing will be lined with 1/2" foil backed insulation. I'd like to use foam backed foil, but this will not be easy to install because the thing is totally seamless. There is no way to remove the rack rails. I'm not sure the foam will bend enough to push into place. I may have to use fiberglass batting held in place with foil tape, which is untidy

[Walter Mooney]

Tom, why not insulate the outside if you can’t do it adequately on the inside? Seems to me that that should still work. Insulate the top, two sides and the back, and leave the front as just the glass so you can see in there and monitor what you wish without opening it. Best of luck. Keep us posted on your solution(s) and your results over the next few months.

[tom lucas]

Tom, why not insulate the outside if you can’t do it adequately on the inside? Seems to me that that should still work. Insulate the top, two sides and the back, and leave the front as just the glass so you can see in there and monitor what you wish without opening it. Best of luck. Keep us posted on your solution(s) and your results over the next few months.

That might be a good idea Walter. I can get more insulation that way. Though moving it may not be as convenient. Maybe build it to drop on like a 4-sided hat, and just let it sit on an insulated bottom. We'll see once I get all the parts in hand. It's my Saturday project.

[Dwayne Watt]

experimenting is your friend. The weak link with mine it temperature monitoring. My next need is for two thermometers one for the cabinet interior, and one for the center of the wood. I want a way to check both without having to open the door. I currently have 4 53 watt (75 replacement) regular bulbs. I only use all four for making red neck ebony. My bulb holders sit on the bottom above good size holes for the wire's and to let air in. There is a vent at the top. The convection creates good air flow. It is also very handy for killing bugs and speeding up glue & paint.
Ok, I'll bite...what is red neck ebony?

[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-Thermometer-Hygrometer-Temperature-Fahrenheit/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.