I have a question about wood expansion on a coffee table I am building out of red oak. It will have a bottom shelf that will go inside the legs at either end. I would like to make the shelf as tight up to the legs as possible so that you do not see a gap every time you look at it. The problem is that if I do this there will be no room for expansion of the wood at the point where the leg and the shelf come together. The shelf will be 20 1/2″ wide a the point it goes between the legs. The overall width of the shelf is about 24 1/4″ and it is 5/8″ thick the legs are 21/4″ square. If I do have to leave a gap how much would you recommend. The shelf will be supported on rails and therefore will not be notched in the legs.
Thank you
Robert
Replies
horatio,
simplest is to use plywood and band the edges of the plywood.
Mike
horatio,
I don't know where your located but if it were my unheated, unconditioned shop I'd leave no space at all for expansion.
It's August and its been wet. I figure the wood is about as expanded as it's ever going to get. So I'd go for a tight joint.
Discussions on here seems to suggest a 1/4" per foot is a good number for expansion and contraction. I take a wag as to where the wood is in the expansion/contraction process at any given time and work from there. Usually I just assume it is about half way at any point in time. If that were true in your case then your piece would expand another 2-3/16" between the legs. I think however, your wood will shrink in the winter quite a bit and leave an 1/8" gap between each leg and the plank...no sense making the gap larger.
I hope someone has better advice but that is what I'd do...make the joint tight.
Mount the shelf to the legs, with whatever method you want. Suck it up tight when you do.
Assuming that the top is also red oak, and you have the grain orientation the same on the top and shelf: the moisture expansion will be equal for the top and shelf. So, the legs pinned to both will move with them in equal amounts.
If your design has the grain going opposite directions, it is the time to change it. Good design is durable.
Even if you are attaching the shelf to the rails, why not make a notch in the leg that the shelf slides deeper into when expands, and less deep when it shrinks.
I used Plywood with solid edging and ran it tight to the legs .
Sorry about the fuzzy picture .
dusty
Robert,
Here is a relevant FWW article from issue 198:
http://www.taunton.com/finewoodworking/ProjectsAndDesign/ProjectsAndDesignPDF.aspx?id=30589
Lataxe
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