Wanted to share my cheap-o solar kiln designdesign

[Jesse snowden]

So I just wanted to share how I've been drying my slabs. Paid 150 for the trailer frame, 150 for building supplies. Using a big floor fan plugged in. Plans are to get a solar setup going, but no need right now.

The idea for the kiln was to satisfy a few needs:
be mobile
Be cheap
Have multiple uses

The walls all come off to become a regular flat bed for camping or whatever. The last photo is the temp inside the bubble.

Cheers!

 

[Quietfly]

Nice job. Reminds me of my girlfriends in college, multiple uses, mobile and practical.....

 

[kjudd]

Would black plastic work better for this? I have a trailer and black plastic I could use for this.

 

[sweepleader]

Black or clear might get hotter, how hot is too hot? What temp is best/good for what kind/thickness wood?

 

[Jesse snowden]

I believe clear will actually get the air hotter. And if the average air temperature is 115°-120° inside the plenum, the surface of the plastic will likely get hotter than that on a sunny day. I've seen a video of a guy with black insulating foam board on the inside of his solar kiln that started to melt.

I'd stick with clear. String reinforced poly is what I used.

 

[Franny K]

I have heard, in person, that 165 degrees F is the limit at which planing or making moldings have issues. He was talking about dulling cutters and I think also chipping instead of a desired finish. Just talk. He uses natural gas for heat and an electric dehumidifier. Not sure if that was from others, from experience, or any combination. Maybe 165 was the temperature to be sure that all eggs from insect type organisms are surely killed off. There is a temperature at which he talked about the cutter issues I mentioned above.

 

[Pauls_Workshop]

Black or clear might get hotter, how hot is too hot? What temp is best/good for what kind/thickness wood?

Hi, um, I had multiple classes in heat transfer back in college for mechanical engineering and actually calculated solar radiation equations and such. Thermodynamics and Heat Transfer are fields of mechanical engineering. Black body radiation is always the greatest possible heat absorption from thermal radiation (nothing to do with nuclear radiation). So Black things will get the hottest from just the thermal radiation. Red is real close and gets 2nd hottest. Now clear for the plastic though would let more solar rays pass through. The max possible heat absorption into the kiln would probably be with completely black surfaces on the inside of it, and the clear cover on top. It gets kind of complicated though, because each reflection of the thermal radiation loses some of it's original potential. I'm not sure how hot we want it to get in there. Is the fan setup with a temperature sensing device to trigger on at certain temperatures (much like a car radiator cooling fan) and shut off otherwise? That would be ideal.

Around a campfire, to get the max possible heat into you, wear black or red clothing! AND, setup a shiny silver reflective blanket or many of them behind you, above you, and to the sides of you. This captures even more from the reflected thermal radiation. Setting up a few more reflective surfaces behind the fire would add even more, to the limit of having the whole fire area surrounded by reflective surfaces, with only a small chimney and small air inlet area to feed and exhaust the fire.

I really like this idea. I've got a trailer and might want to think about something similar there. Would save years on drying time and help with the problematic wood too! Neato! - Paul, ME on the side

 

[mauldinoutdoor]

How long would it take to get 2" oak down to acceptable moisture levels? Give or take.

 

[Jesse snowden]

Well it is 3" white oak that's in there right now. The tree was cut down in mid march and slabbed the same day, I finished the kiln on april 6th and it's been drying in there. Last I checked the internal MC was about 25%. Total guess here, but I'm gonna say it's probably at around 15-18% today?

So I'd project these slabs will be at 10% in 2 more months maximum. So 4-5months in total from living tree to workable wood. Keep in mind though, I'm making slab tables and using black resin to fill all the cracks. Of which there are MANY

 

[mauldinoutdoor]

I new to milling and still amazed how much wood shrinks and how fast it does as it dries. All my projects so far have been with fresh cut wood built with accommodations for shrinkage but I built side walls for a dump and within a month, I've lost 2" in 6' at least in height. 4-5 months is a long time but a whole lot better than the alternative. Thanks for the response

 

[Jesse snowden]

I've talked to a few people that mill white oak. They let it air dry for a year before butting it in the kiln, because white oak is so prone to cracking. So you take a bit of a hit in that respect if you're putting green wood in the kiln, but it can still be used. Cheers

 

[bobbobbobbob]

My drying shed is currently stuffed with white oak. Because of the cracking problem I plan to air dry all of it. It should be down to 12% by the end of the summer. Most of it will be used for furniture and the balance for turning and maybe a couple of mantles.