Comment on 2x2 lumber at Home Depot is now 1.28x1.28. Nominal size is supposed to be 1.5
intensely_human@lemm.ee 5 months agoI’ve not really encountered this wood expanding and contracting thing. Are you sure?
SchmidtGenetics@lemmy.world 5 months ago
usualsuspect191@lemmy.ca 5 months ago
True, but the amount they shrink and grow across the grain tends to be proportional. A 2x4 is very rarely measurably different from 1.5"x3.5", but a 2x10 (like you’ve shown) is 1.5"x9 1/4" but is often anywhere between 9 1/8" to 9 3/8"
captain_aggravated@sh.itjust.works 5 months ago
Absolutely sure. It’s not really a factor in construction because of how the structure is engineered, but woodworkers have to constantly think about it.
Wood expands and contracts across the grain, but not so much along it. If you take a board that has been in a dry environment, put it in a humid environment, and allow it to acclimate, it will increase in width and thickness but not in length. At the microscopic level, wood is kind of like a bunch of ropes glued together with sponge, as it soaks up water the sponge wants to expand but the ropes don’t let it expand along their length.
Us woodworkers have to think about that when building things like doors, which might fit fine in the winter and then stick in the summer. It’s why we build frame and panel doors like this:
Image
The large panel in the middle can expand and contract so much that it might be a problem, so we literally put it in a box. The outer dimensions of the frame are made mostly of the length of boards so it won’t expand and contract much, and the panel rests in a groove in the frame, not nailed or glued in place so that it can safely expand and contract as it wants to.
Attaching wide boards end-to-face can even present a situation where the boards want to move in different directions and they’ll eventually break each other.
You can even calculate the amount of wood movement given the species, of the wood, the dimension of the board and the amount of moisture change, you can read about it here.