One of the great things about woodturning is the ability to use free wood that you can find or harvest yourself rather than relying on store bought lumber. Finding logs on the side of the road or taking down a tree yourself is a great way to not only save money, but also gives you access to woods not normally available in stores.
Once you have the wood to turn, the issue becomes how to dry it. Whether you're roughing out bowls to then dry and finish turn at a later date, or milling up spindle blanks, or even just drying full bowl blanks, eventually the wood needs to fully dry before a piece can be finished. If you have a lot of time, this isn't an issue, but if you're impatient, or especially if you're trying to get items finished to give as gifts or sell, waiting months or years isn't a great option.
There are many different ways to speed up the drying process, from light bulb powered drying boxes and kilns, to microwaving individual bowl blanks, but the one that appealed to me the most was a solar kiln. Put simply, a solar kiln is a box with a clear lid that allows sunlight in, but traps radiant heat.
There are dozens or hundreds of designs for solar kilns online, but they're mainly set up for drying large quantities of lumber, and while "inexpensive" at just a few hundred dollars to make, they didn't really fit for someone making the small volume of items I make. Knowing I wasn't spending hundreds of dollars on materials and wiring up multiple fans to a box in the middle of my yard, I decided to try making my design.
I found an unused clear plastic Ikea tub in my basement that I thought would work well for a 'lid', it was around 30"x22"x7". I had a bunch of scrap 3/4" and 1 1/2" material laying around, so I started by making a box which was 20"x29"x19" tall. I designed it so the lid would sit down on the box slightly. The entire design was based off of getting as good a seal as I could with this specific tub.
Once the box was assembled, I put the lid in place and added some ripped down 3/4" material to the outside to act as a lip for the rim of the tub, and added some self adhesive foam weather stripping. This lip gave the edge of the tub something to sit on, and provided a pretty good seal, making it mostly airtight.
After the lip was in place, I spray painted the inside of the box black to absorb as much heat as possible, and drilled three small (1/4"ish) holes in the back panel at the very bottom. On the front side of the plastic tub near the top I drilled 3 more holes. These allow for some ventilation, the hot air rises and pulls the moisture out of the top, drawing cool dry air in from the bottom. Most solar kiln have fans that aid with this, but this seemed like a good start.
At this point, all that was left was to fill the kiln up, put the lid on and see how hot it actually got.
For being thrown together with scrap wood, the kiln actually holds a decent amount of wood. For the temperature, I was doing most of my testing when it was between 70 and 85 outside, I was routinely reading 130 and up to 140 degrees inside the kiln. That's right in the ideal window for drying wood, and I've already been able to dry quite a few blanks through this little kiln.
There are some pretty obvious drawbacks or limitations. The kiln isn't all that big, so for anyone producing larger volumes it may not cut it. It's also pretty specific for whatever size tub you have available, and the 3/4" wood walls don't offer much insulation so it cools off pretty quickly. The main issue I've run into is some pretty big differences in temperature between the top and bottom of the kiln. Wood at the top is drying a lot faster than wood at the bottom, which is pretty obvious. My plan is to solve this with a small solar panel hooked up to a computer fan which will circulate the air inside the kiln, hopefully making a more consistent temperature throughout.
Overall, it's pretty ugly, but for something that cost $0 and took around an hour, I'm pretty happy. Some minor adjustments and a $20 solar panel/ computer fan combo addition should drastically increase performance. Even as is it shows that it's definitely possible to make a solar kiln for under $30 or even free if you have enough scrap wood lying around, that's able to dry a few dozen bowl blanks at a time in weeks, rather than months or years.
Comments
Post a Comment