Woodworking Talk banner

Kiln drying logs

2K views 10 replies 6 participants last post by  Da Aardvark 
#1 ·
The previous owners of our house left a kiln that they used to fire dolls with. Anyone use a kiln to dry logs? I was wanting to cut some blocks out of a few pieces of maple firewood I have to make bandsaw boxes with. I want to be sure the wood is dry enough so it doesn't crack. Any thoughts???
 
#4 ·
Just put some pieces of firewood aside for a year or so. In kiln drying, steam is injected at stages during the process. The outer surfaces of the lumber dry long before the interior core and the steam wets the outer surfaces to keep the moisture in equilibrium. 1" red oak will be in a kiln for 30 days. Thicker lumber is much more difficult to kiln dry and it takes forever. Even finding 4" KD lumber is rare. It's very difficult to prevent thicker pieces from checking. Try slabbing off some larger 12" - 16" log pieces, paint the ends to reduce quick moisture loss and stack some in the shop. You won't know if they will split but you may get some workable pieces by cutting around or splitting open along checks.
 
#5 ·
There is a lot more to drying wood than just heating it in an oven. Each species has a maximum rate that moisture can be removed from it, and this rate changes based upon the thickness of the wood, as well as the initial moisture content. The drying process involves taking daily measurements of the amount of moisture content loss and adjusting as needed to stay within a narrow window.

Although dehumidification kilns dry between 90 - 140F, conventional kilns dry at much higher temps (up to 180F).

Additionally, wood dries very poorly in log form. If you want to dry it before machining it, it is much better to mill or turn the blank to a dimension that is close to the targeted final dimension, as opposed to leaving it in the log.
 
#6 ·
scsmith42 said:
There is a lot more to drying wood than just heating it in an oven. Each species has a maximum rate that moisture can be removed from it, and this rate changes based upon the thickness of the wood, as well as the initial moisture content. The drying process involves taking daily measurements of the amount of moisture content loss and adjusting as needed to stay within a narrow window.

Although dehumidification kilns dry between 90 - 140F, conventional kilns dry at much higher temps (up to 180F).

Additionally, wood dries very poorly in log form. If you want to dry it before machining it, it is much better to mill or turn the blank to a dimension that is close to the targeted final dimension, as opposed to leaving it in the log.
Wow... Thanks for that. There is a lot to it.
 
#7 ·
In North America, outdoors, under cover, you can anticipate wood to air dry at a rate of approximately 1" per year. From both sides then, 2" slabs (ventilated with stickers) might be down to a Moisture Content of 12- 14%. That is as good as it gets.

Indoors, the drying rate is far faster to a MC of maybe 4% and the risk of checking/splitting is enormous in log pieces. Kiln-dried soft wood might come out at 24%, kiln-dried hardwoods at 15%.

I encourage you to try to rush the process, just to see what happens, hoping that you aren't in love with the wood.

If you have a green log. Nice wood but one side is really ratty, here's the deal: Totem pole style, cut 1/4 of the log away, all down the ugly side. Toss that. Strip the bark. Paint the ends to slow the water loss, to approximate the loss from the tangential surface.
Wait a year per inch of thickness. I have a 6" x 24" bit of willow that set up without a mark that way.

If you're serious, get 2-3 cords more wood and set that up while you're waiting on the first lot. The furniture shop down my street harvests 5 cords of wood each spring. They strip the bark and into numbered bins it goes. The skinny wood for hiking sticks and canes is for 2014. The furniture logs (4"+) is for 2016. If you get serious, that's how it's done.
 
#8 · (Edited)
for pieces that small you could build a wood box, and put a light bulb in it and achieve 140 degrees plus, install a fan to circulate the air in it, wood will be done in a week or 2, get a tester to check moisture content of the wood so you dont overdry and check the crap out of it, and like mentioned above, trying to dry an entire piece still in log form isnt gonna work out very well, the stresses in the wood will be too great and it will check like crazy and the piece wont be good for anything but a crap ton of pen blanks
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top