Green wood to seasoned in one hour!

[Ron Sardo]

I didn't read this whole thread, but here is what I know about vacuum kilns based on what I learned from a friend who has a 20' x 9' vacuum kiln. (Yes that is feet)

You'll still need heat with a vacuum kiln to raise the temp to around 150°F~160°F

Lumber cut from recently felled trees would still take months to dry in a vacuum kiln.

Wood that been "seasoned" a few months and then placed in a vacuum kiln may take a few days (3~14) depending on the species.

Yes, I did try and placed a few rough outs in his kiln and the warped nicely 🙁

 

[MichaelMouse]

What is the point of rapidly removing the moisture? Moisture is not the reason that wood warps and cracks -- it cracks, as Dr. Chen stated, when moisture is removed too rapidly which leads to steep moisture gradients within the interior of the wood. That translates to steep stress gradients -- for the benefit of the non-technical person, is another way of saying "warps and cracks like the dickens".

If I were drying a roughed out green wood bowl, I don't believe that I see much difference between using a vacuum pump to remove the moisture versus laying it out in the hot summer sun in Texas.

You'd SEE a difference, if, as in the process described above, they maintained the RH in the kiln properly. The moisture drawn from the interior (or evolved by the microwave) will migrate to the surface, which, as in a conventional kiln, is maintained just around the FSP/EMC by control of the RH. I weasel my microwave stuff a bit to do the same, bagging the piece to stop the surface check that can grow by mechanical stress into a split.

The conventional kiln is not capable of continuously pulling moisture by vacuum or pushing it to the cooler surface from the insulated and therefore warmer interior, as with a microwave. That's why they go through steps of warming, venting and cooling, and rewarming.

 

[robo hippy]

Well, I hadn't checked on this thread for a while, and it is interesting to see how it has gone. There was a guy locally who was using a vacuum kiln for drying lumber, and I got quite a bit from him. It worked like air dried lumber as in when you ripped a board on your table saw, you got shavings, not dust like from standard kiln dried boards. You can resaw an 8/4 board, and there was no spring at all to them. Layers of lumber were laid out with an aluminum extruded sheet in between each layer. The sheets had anti freeze run through them as a heat source. After filling the kiln, they would bag it, kind of like the vacuum presses that are used for veneering. The vacuum would then be applied. Drying time was about 8 days. Water would boil in his vacuum at about 110 degrees. I don't see why this couldn't be applied to turning blanks and rough turned bowls, but don't think it would be practical. It might work better for drying thicker blanks before turning, but again, might not be worth all the effort.

robo hippy

 

[Bill Boehme]

It is the one hour part that I saw as being unrealistic. I know that reducing the pressure would speed up the drying, but the process would also require carefully controlling humidity and temperature -- something that is not realistic or practical for a one hour process or even one or two days.

Now, if the wood were mesquite, I think that the process would work fine. 😀 Charlie, I hope that you had the opportunity to meet Larry Roberts while you were here. He is a wonderful gentleman. I know that you will enjoy your mesquite. If I had known when you were here, I would have given you some large chunks of dry mesquite. Turning dry mesquite is not as much fun, but it still turns easily enough.

 

[Bill Boehme]

Bill, mesquite on the trail to virginia 😀

Charlie, how in the world did you get that big pile of mesquite into your pickup truck? 😀

 

[Charlie Knighton]

Bill, i am sorry i missed Larry Roberts, i tried to contact him thru Chase but things did not work out. i was only in texas a couple of days and had to go to plan C to acquire some mesquite. that was an amazing pile of mesquite and Butch is quite the catbird. after acquiring the mesquite i did do a bit of looking

 

[Ron Sardo]

Well, I hadn't checked on this thread for a while, and it is interesting to see how it has gone. There was a guy locally who was using a vacuum kiln for drying lumber, and I got quite a bit from him. It worked like air dried lumber as in when you ripped a board on your table saw, you got shavings, not dust like from standard kiln dried boards. You can resaw an 8/4 board, and there was no spring at all to them. Layers of lumber were laid out with an aluminum extruded sheet in between each layer. The sheets had anti freeze run through them as a heat source. After filling the kiln, they would bag it, kind of like the vacuum presses that are used for veneering. The vacuum would then be applied. Drying time was about 8 days. Water would boil in his vacuum at about 110 degrees. I don't see why this couldn't be applied to turning blanks and rough turned bowls, but don't think it would be practical. It might work better for drying thicker blanks before turning, but again, might not be worth all the effort.

robo hippy

That sounds like what my friend has.

It is the weight of the layers of wood and aluminum combined with the anti freeze the helped keep the wood from twisting. He would also add a few hundred pounds of cement on the top sheet.

The few bowls I tried in his kiln warp pretty good.