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Forum topic by lumberjacques posted 04-16-2009 10:19 PM 1198 views 0 times favorited 7 replies Add to Favorites Watch
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72 posts in 3312 days

04-16-2009 10:19 PM

Topic tags/keywords: question

ok, i am going crazy here. my woodshop (referred to as “da dunjin”—don’t ask), is in my basement. i live just outside the island of montreal, canada. i have central heating, oil and electric hybrid. the dunjin is more or less 20 degrees Celsius (68 f), and the humidity level is in the mid 30’s %. sounds just about right?
well, my problem is when i resaw wood, from 0 to 8/4, after a while, the plank warps. yes, even 8/4!! before cutting, my wood reads (assuming my meter is correct) anywhere between 7 to 11% moisture.

1) what SHOULD the humidity level in the dunjin be?
2) how can i EASILY maintain it?
3) am i doing something wrong during the resaw?
4) is it a problem of transition between heating season and non heating season?

any help will be MIGHTILY appreciated; i have some real beautiful boxes with lids that are warped an average of 1/16…..


7 replies so far

View 8iowa's profile


1580 posts in 3726 days

#1 posted 04-16-2009 11:16 PM

Actually, at 68 degrees F, a relative humidity in the 30’s % range is pretty dry. New wood, just brought into your shop, will begin to dry further, perhaps warping in the process.

You need to let your wood acclimate in your shop for at least two weeks before doing any cutting or planing. Stack it horizontally with “stickers”, vertically spaced between boards, so that drying will be uniform.

I don’t use a moisture meter. I see a lot of mixed reviews on their relative accuracies.

-- "Heaven is North of the Bridge"

View Kindlingmaker's profile


2656 posts in 3491 days

#2 posted 04-16-2009 11:50 PM

...and no matter how dry or wet your wood is it may well relieve stresses when cut and do all sorts of ugly things (sometimes).

-- Never board, always knotty, lots of growth rings

View Mike Lingenfelter's profile

Mike Lingenfelter

503 posts in 4079 days

#3 posted 04-16-2009 11:56 PM

Most wood will move when you cut it, even if it is well dried. It’s a good practice to cut your boards oversized and let them move if they are going to. Give them a week or so, to see what they are going to do. Then finish working the boards to their final size.

You mentioned resawing. If you take an 8/4 piece of lumber and resaw it into thinner boards, you will almost always see the boards bow/warp. All boards have some amount of tension in them, and cutting the board will release that tension. The strategy again is to resaw the board oversized and let it set for awhile. Then bring it to finial thickness.

View lumberjacques's profile


72 posts in 3312 days

#4 posted 04-17-2009 01:39 AM

the thing is that in some cases, i make the lid, whether one piece or framed, and it’s only SOME time later that it warps….gggrrrrrrrr…...
if mid 30’s humidity is sorta low, what is a recommended % ?

View 8iowa's profile


1580 posts in 3726 days

#5 posted 04-17-2009 03:29 AM

Relative humidity is very much misunderstood. The key word here is “relative”. In cold sub freezing Winter temperatures, the air can hold very little moisture. When your furnace takes in this very cold air, which may be holding almost 100 % of the moisture that it can hold, and then heat this air up to 68 degrees F, the humidity will drop to 30% or lower. This is because air at 68 degrees can hold a lot more moisture than the cold air. Thus relatively speaking, the humidity is much lower.

A smow making machine sort of operates in reverse. Warming air, saturating it with as much humidity as it can hold, and then blasting it out into the below freezing air, which cannot possibly hold this much moisture, thus it precipicates snow.

Actually, in Northern climates with long Winters, like where my shop is in the Upper Peninsula, it would be a good idea to add a humidifier to the furnace in order to keep your air from becoming so dry.

-- "Heaven is North of the Bridge"

View miles125's profile


2180 posts in 3971 days

#6 posted 04-17-2009 04:25 AM

Higher or lower humidity isn’t the culprit. Quick change probably is. And don’t set resawn wood too near any concrete.

-- "The way to make a small fortune in woodworking- start with a large one"

View TopamaxSurvivor's profile


18246 posts in 3641 days

#7 posted 04-17-2009 07:52 AM

miles125, What is the deal with concrete, does it secrete moisture into wood?

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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