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Author Topic: Wood fired dry kiln  (Read 9517 times)

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Offline Eljay

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Wood fired dry kiln
« on: January 19, 2011, 09:23:40 AM »
I was asked, in the Saw mill forum,  for a description of the wood fired dry kiln I built to dry white ash and tulip poplar. I thought it more appropriate to post it here. So here is the description.
My design is based on some of the information from "The Dry Kiln Operators Manual". This is still available from the U.S.Dept of Agriculture. Handbook 188. If you do a google search for the title, you can download it as a pdf.
Once I dried all of the lumber for the interior wood work of my house, I dismantled the kiln so my description is from memory.
The kiln was a wooden structure about 8 feet high and 6 feet wide and 105 inched deep. The boards went in the long way and stickered with 2' wide 3/4" stickers. At the top of the kiln I had two fan blades that were driven by a single motor mounted on the outside of the kiln. The fans circulated the air across the short side of the stack. A baffle went from the fan mounting to the top of the stack. It was hinged to accomodate different stack heights. Theoreticaly, this circulated the air in a circular fashion through the stack. The hot air was introduced at the top of the kiln on the suction side of the fans.
The hot air was made in a home made wood stove. The fire box was about 4 feet long, 3 feet wide and high. It was surrounded by a second steel box. This created a plenum with a 4 inch space between the firebox and plenum wall. A blower moved the hot air from the plenum to the top of the kiln.
I had several temperature controllers to controll the wood stove and the blower so that I could follow the kiln schedule for what ever species I was drying. In practice this proved unnessesary because the kiln temperature was really controlled by the moisture content of the wood. I used a Delmhorst moisture meter with several remote probes in various parts of the stack to monitor moisture level. Essentially, the kiln temp vs moisture content followed the recommended kiln schedule all by itself. As the moisture went down, the kiln temp went up. The woodstove and blower ran all of the time. All I had to do was feed the stove.
A kiln run generally lasted ten days to two weeks starting with air dried  1 inch stock. I dried the wood down to 6%. With the kiln still hot, I put in the wand from my steam cleaner to bring the moisture up to 8% and eliminate case hardening. As I approached 8%, I took samples and checked to see that all stress was releived. Going from 6 to 8% this way took less than four hours. Originally I had several spray nozzles that I was going to use for stress relieving but these did not work out.
I was real happy with the drying results. I made all of the flooring, doors and trim for my house. I would guess that if I counted all of the hours and material I used for this project, I would have been better off pumping gas and buying the wood. After looking at the reults, I'd do it again.

Offline paul case

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Re: Wood fired dry kiln
« Reply #1 on: January 19, 2011, 09:40:57 AM »
thank you for this post.  pc
life is too short to be too serious. (some idiot)
2013 LT40SHE25 and Riehl edger,  WM 94 LT40 hd E15. Cut my sawing ''teeth'' on an EZ Boardwalk
sawing oak.hickory,ERC,walnut and almost anything else that shows up.
Don't get phylosophical with me. you will loose me for sure.

Offline laffs

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Re: Wood fired dry kiln
« Reply #2 on: January 20, 2011, 07:19:10 PM »
thanks for the post Eljay
did you condition with steam  or straight water mist? why didnt the spray nozzles work ?
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Offline Eljay

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Re: Wood fired dry kiln
« Reply #3 on: January 21, 2011, 03:54:52 PM »
My first attempt at conditioning was using a mist. I used nozzles that were designed for misting vegatables to keep them fresh.
In retrospect, I don't think they delivered enough water fast enough. The steam from my steam cleaner was delivered at a much higher rate.

Offline Troublermaker

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Re: Wood fired dry kiln
« Reply #4 on: January 21, 2011, 07:17:04 PM »
When I was building my house 25 years ago I was working at a sawmill that cut a lot of grade oak. I got the lumber grader to pull me some good red and white oak to build all of my cabinet from. We had a couple of old chip trailer that was no longer use on the road. The boss gave me one. I brought it home in the winter and patch all the holes but one cut in it to let out air when blowing chips into it. In that one I rig up a stove after loading my lumber in it. I painted the end with some old paint that I had. I put in a fan that ran all the time. Then I would build a fire in the stove. I could get it up to a 100 even if it was 40 outside. In the summer I didn't have to have a fire. The sun took care of the heat. I donít know what the moisture was but the cabinet man said that it was too dry so he laid it out in his shop to let moisture build up in it slowly so that he could work with it. It works so good that I use to sell some lumber to a couple of cabinet builder.

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