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No temp control in shed, always high EMC, what do I do about wood movement?

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Forum topic by Spikes posted 01-01-2019 06:08 PM 884 views 0 times favorited 7 replies Add to Favorites Watch
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Spikes

125 posts in 528 days


01-01-2019 06:08 PM

Topic tags/keywords: question

Hello all, happy new year,

as some of you know I’ve been restoring an old metal shed, I put a wood stove in it which is enough to get my hands functioning, but otherwise the place is cold and more or less as dump as the forest outside.

I’ve just got a moisture meter (sensor type, wanted to use it at the lumberyard too without poking holes in the wood) and basically most lumber I have in the room is at 15% or higher apparently (mostly all pine, lots fo 2×4s, some doug fir). This stuff was supposedly kiln dried, but I’m assuming that by sitting there it re-absorbed moisture from the environment and stabilized around 15%.

The question is, if it’s true that for furniture making I should be aiming for 6%-8% EMC, and I cannot maintain that level in the shed, what are my options ? I’m almost ready to start building my first non-shop project (a bed, yay!) and worried that when it goes into the house with temp control it will just split and crack all over the place as it acclimatizes to the very different EMC. Is that indeed likely to happen as the literature on moisture and wood movement seems to suggest? Anything I can do other than adjusting the design for as much wood movement as possible? I’ll be using doug fir and the stretchers will be connected to the legs with bridle joints, but I meant to glue them…

thanks for any thoughts,

-- Don't worry about making progress, worry about practicing. If you practice you will make progress even if you don't want to.


7 replies so far

View bondogaposis's profile

bondogaposis

5521 posts in 2834 days


#1 posted 01-01-2019 06:24 PM

Construction lumber is not kiln dried to level of hardwood lumber. Moisture content for construction lumber is 18-20%. If yours is 15% it has dried some. It would certainly be better if you could get that lumber drier by bringing it inside into a heated space, like under your bed. Either way you will still have to allow for wood movement in your construction.

-- Bondo Gaposis

View Walker's profile

Walker

160 posts in 955 days


#2 posted 01-01-2019 06:33 PM

If you have the space for it, I would store your lumber in the room where your finished project will be. Take the pieces to your shed when you need to work on them, then bring them back inside. It’s a bit of a hassle but it could help.

-- ~Walker

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Spikes

125 posts in 528 days


#3 posted 01-01-2019 07:52 PM

thanks for the pointers, agreed it’d make sense to bring the lumber inside and that’s probably what I would do.

That said, I’d like to confirm with people here – would it be indeed a crazy proposition to build a bed with lumber at 15% EMC? am I guaranteed, despite best efforts to allow for wood movement, that things will end up poorly? or is it feasible with the right design?

thanks,

-- Don't worry about making progress, worry about practicing. If you practice you will make progress even if you don't want to.

View ArtMann's profile

ArtMann

1425 posts in 1299 days


#4 posted 01-01-2019 10:55 PM

You may be operating on a false assumption about wood movement is unpredictable. This is only partially true. There are really two problems and they are only slightly related. First, there is a tendency for wood that isn’t dried properly or is just poor quality to warp, cup or bow. Changes in moisture content can bring this on but you can generally see that ahead of time. The only way to get rid of it is to joint and plane material away until the wood is flat and straight.

The other wood movement is the property of the wood to change dimension in a very well understood and predictable way with changes in humidity. That is the property you can’t see but should worry about. Wood doesn’t expand and contract the same way in all directions. You can actually predict how much this movement will be and adjust your design to compensate. The classic example is designing a table top so that the breadboard ends allow expansion of the main table as it changes dimensions during the year without buckling or cracking. There is much to learn about this type of wood movement but it really is necessary if you want to build good solid furniture. Below is a web page that allows you to study the affects of changes in humidity of various species with changes in moisture content. If you can understand how this works, you can predict whether and how much trouble you will have with wood movement.

http://www.woodbin.com/calcs/shrinkulator/

View Spikes's profile

Spikes

125 posts in 528 days


#5 posted 01-02-2019 02:56 AM

@ArtMann, that’s helpful, thank you. I’ve tried to use the calculator you linked , not sure I fully understand it. Assuming a change of moisture from 15% to 8% indoor and a 2×6, so 1.5×5.5 inches, it seems things won’t shrink more than .11 (altho not clear about radial vs tangential). That’s gonna influence the bridle joint, I’ll need a bolt to keep things together when the joint comes a bit loose from the shrinking.

For the length of it, my understanding is that wood doesn’t change much in that direction, just across the grain, so not sure that matters.

-- Don't worry about making progress, worry about practicing. If you practice you will make progress even if you don't want to.

View Robert's profile

Robert

3516 posts in 1963 days


#6 posted 01-02-2019 05:29 PM

You are rightly concerned, but yes, IMO it is feasible with the right design. You’re not going to get much change in 6” with 4-5° drop in MC. Avoid joinery that would be affected by shrinkage. Years and years ago I built beds over drawers for my boys. I used 2×6’s right out of the lumber yard t/g joinery with pins. Only one board cracked through a dowel hole which was easily fixed with glue & clamp.

That said, I would put in stickers inside house for a few weeks before milling.

Check the Samurai carpenter video about wood movement.

-- Everything is a prototype thats why its one of a kind!!

View Spikes's profile

Spikes

125 posts in 528 days


#7 posted 01-02-2019 10:23 PM

thanks @rwe2156 , could you please expand on the joinery you used? I’m guessing t/g joinery means tenon and groove, but then I’m unclear where/how you used the pins, and when you say pins do you mean dowels? I was thinking of going with something like this and wondered if alone with no bed bolts or other fastener (no glue) it’d stay in place when the wood moves:

If I just used t/g for the siderail, would I then put through a dowel to keep things in place and make the dowel hole oversized? is that how it works to fasten it but let it move?

thanks,

-- Don't worry about making progress, worry about practicing. If you practice you will make progress even if you don't want to.

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