Solar Resources - Custom Solar Kiln
Drying american black walnut throroughly is not always easy. We have been making gunstocks for 20+ years and have always used air dried material.
We start by cutting the trees locally or buying logs. Ends are always coated with anchor seal as soon after felling to reduce cracks and checks. “Bought” logs are never coated when we buy them so sometimes we have to work around defects. All our blanks are worked by H.D.S. Inc., a local bandsaw operator who is one of the best I have ever seen at sawing figured wood. After sawing, we stick and stack the lumber under tarps or an airy shed. Usually, our material is air dried at least 2 years, reducing the moisture content from 14 to 18%. Before we added our dry kiln, we had to dry this 2-3/4 to 3-1/4” stock around 3 years to get it to 8 to 12% where it was useable for gunstocks. This is a very humid area (except in winter) and air drying simply does not give very consistent resluts. We tried commercial kiln drying, but most drying operations dry your wood too quickly resulting in more splits and cracks and damage. Also, it seemed the color was sometimes affected in a negative way.
Our answer to this has been to use a self-built, passive solar kiln. My sawyer and myself attended a course at Virginia Technical college(VTI) in Blacksburg, VA to learn how to build and operate a solar kiln. This type kiln takes advantage of the sun to supply the heat for drying and uses 2 electric fans to circulate the air. Our kiln is approximately 16 ft. long and 10 ft. wide; holding approximately 1200 board ft. of stock blanks. This kiln generates 120 to 140 degrees fahrenheit which is enough to adequately dry this thickness of walnut or maple. The boards are cut into approximately 4 foot lengths, sealing the ends with anchor seal and stacked on pallets to a height of 4 feet. Three quarter inch stickers are placed between each layer to allow air flow. This lumber is at approximately 16 to 20% moisture content when stacked inside. Our last load was placed in the kiln on April 27th, 2009 and we started removing boards on June 1st. The moisture content was calculated at 8 to 10% throughout when removed. When removed, a pallet at a time, we measure and mark each board with m/c and resaw them to rough blank size, removing sapwood and defects. Immediately after the resaw, we plane each piece and grade it. (click here to learn more about wood grading>>) The last step is to coat the entire blank with a vapor barrier and stack on a shelf.
The real beauty of the solar kiln design is that the air circulates as long it is 100 degrees fahrenheit. For more below 100 degrees, the fans cut off and the more moist, cooler air creeps back into the kiln, which dosen’t “shock” the blanks as does a commercial kiln. We also made some modifications to the Virginia Tech design, such as adding a plenum to speed up air flow and added extra insulation to preserve our free heat. The only operating cost to this kiln is the two electric fans at approximately $35.00 per month. One of the hardest things to do in drying our lumber was the fancy burls and feather crotches that consistently hold more moisture than the straight grained wood. This kiln will keep the highly figured wood within about 1-2% moisture content of the rest. This makes for a much better, more consistent and stable product.
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