Bowl Kiln -- The Results

[Bill Bulloch]

Last month I posted a small bowl kiln I had made( http://www.sawmillcreek.org/showthread.php?t=131269 ) and promised to post results of my first bowl drying test.

On Feb 3rd, I roughed out five small bowls, all had a moisture content of over 30. I placed them in the Freezer over night, then let them thaw out for a day. For test purposes, I waxed three of the bowls and left two unwaxed. I ran the kiln with only the fan running for two days, then set the thermostat for 75 degrees, after five day, I moved the thermostat setting to 85.

After two weeks I opened the kiln and checked the bowls. The two unwaxed bowls (Walnut and Maple) had a moisture content of less then 7, with no cracks and a normal amount of wraping at the end grain (see photos).


The Beech bowl was ruined with bad cracks, even though it had been waxed (see photos).

The other two waxed bowls (Bartlett Pear and Magnolia) had a moisture content of between 15 and 20. I put these two back in the kiln and raised the thermostat to 90 degrees. At the end of the third week I check them again. This time the mositure content was less then 7 for the Magnolia and about 10 for the Bartlett Pear. Neither had any cracks. The Magnolia had a very minimal warping and the Bartlett Pear showed no signs of warping (although I suspect I notice some when I get it on the lathe) (See photos).

Although this was not, my any means, a scientific test, the conclusions appear to be that even though waxed bowl take longer they give better results.

Along with these five bowl I, also, put some green planks about one inch thick in the kiln. All of the Beech Planks warped and cracked, where the Walnut, Magnolia and Bartlett Pear did not. So, I gather that Beech needs some special care. I just don't know what that is: Anyone have any thoughts?

Seems that these pictures put themselves in random order. But the order I talked about and put them in were: Walnut, Maple, Beech, Bartlett Pear and Magnolia.

[Steve Kubien]

Very timely as I will be building my drying kiln next week (I get the fridge this weekend). So, I guess I want to continue to anchorseal my stuff? No worries. What I am most looking forward to with the kiln is getting the DNA out of my shop. I find the wrapping to be a pain and the less flammable stuff I have hanging around, the better. Not going to get rid of all of it but every little bit helps.

Steve

[Bernie Weishapl]

Thanks for the info Bill. Good stuff.

[George Morris]

I would like to see what the results are when you turn to finish. Good ideas! G

[Jim Slovik]

This is very interesting. I hope you continue to post your results. Thanks for sharing.
Jim

[John Keeton]

Bill, very interesting, and apparently successful! In doing flatwork, beech is not a favored wood due to instability. I suspect this test bears that out!

I would say that your kiln was well worth the build. Something to consider!

[Brian Weaver]

I have had a small homemade dry kiln for awhile now although I don't do many bowls. The bowls I have dried I have had good success with though. My process is a bit different as I have the fans and light (60 watt bulb) on a timer. For the first week I have just the fans on, 6 hrs on 6 hrs off. The second week I leave the fans on full time and run the light 6 hrs on 6 hrs off. Third week I run everything on full time. This is in a small camper type fridge and the fans I use are some old computer fans I had. I have 2, 1" holes at the top with flappers covering them about half way. Hope this helps although it sounds like you had pretty good success already.

[Bill Bulloch]

I My process is a bit different as I have the fans and light (60 watt bulb) on a timer. For the first week I have just the fans on, 6 hrs on 6 hrs off. The second week I leave the fans on full time and run the light 6 hrs on 6 hrs off. Third week I run everything on full time. This is in a small camper type fridge and the fans I use are some old computer fans I had. I have 2, 1" holes at the top with flappers covering them about half way. Hope this helps although it sounds like you had pretty good success already.

I guess there are a lot of different ways of doing this. I have heard about people who heat their small kilns up to 130 degrees with success. I let my fans run all the time and have a thermostat that controls the two 100 watt bulbs. I have four 3/4 inch vent holes at the top and two at the bottom. I use wine corks to plug them. I have a Hygrometer in the kiln and I check it daily, when the Relitive Humidity gets to 60, I open a vent. When it drops to less than 40, I close the vent. So far I have only had to open one top vent at a time and never have used a bottom vent.

I image that when you run your lights on full time it get pretty hot in there. It only takes about 10 minutes to heat my box up to thermostat level initially. Now I know that the lights have to come on now-and-then to maintain the temperture, but I have never caught them on after the initial heating, so it must be for just minutes at a time.

[Roger Wilson]

Out on woodurningonline.com (where I think you got the design) the pdf from the Irish Woodturners Guild uses the following schedule for drying in the kiln.


"I use a 3-week drying period split into 3 sections:
Week 1 – fan on all the time, light off all the time;
Week 2 –fan on all the time, light on and off in 12 hour shifts;
Week 3 – Fan on/off in 12 hour shifts, light on all the time.

You can see that the drying starts gently with just air circulation
and gradually more heat is added."

[Donny Lawson]

I would like to see a pic of the Bartlett pear when it is finished.
Donny

[Reed Gray]

While I don't do the twice turned bowls, I looked at the crack in the Beech. Really strange, almost looks like it was a fracture that was in the wood to begin with as it didn't crack along any of the lines I would expect it to crack in. Looks like another crack near the rim that is in a different orientation. Maybe it is the beech. I have only had a few pieces of it, but I did get more cracks than I expected.

Has any one ever tried a solar kiln? I just discovered a wood guy close by who uses one. The cycle of hot in the day, then cool at night and humidity going back up to 100% at night is supposed to release stresses in the wood.

If I could, I would experiment with a vacuum kiln as well. I have worked some lumber that came from one, and it worked like air dried lumber. You get shavings when you rip a board, not dust. Same with the solar kiln.

robo hippy

[Bill Bulloch]

Out on woodurningonline.com (where I think you got the design) the pdf from the Irish Woodturners Guild uses the following schedule for drying in the kiln.

"I use a 3-week drying period split into 3 sections:
Week 1 – fan on all the time, light off all the time;
Week 2 –fan on all the time, light on and off in 12 hour shifts;
Week 3 – Fan on/off in 12 hour shifts, light on all the time.
."


Yes, I got my design from woodturningonline.com. but it was not from the Irish guy. It was from Dennis Daudelin http://www.woodturningonline.com/assets/turning_articles/Kiln/Introduction.html He uses a simular schedule, but uses a thermostat to control the temperture in the kiln.

First, in Phase I, he runs it with the fan only, then, Phase II he sets the temperature to 70, then as the wood's moisture level drops, he increases the temperature to 80 degrees. In Phase III, he gives the dry wood a final baking at 90 degrees.

I followed that schedule when I first dried some one inch planks, but when I dried the bowls my eye sight missed and I accedently set it for 75. I just left it at that and moved it to 85 next them baked it at 90 -- same results.