Reply by clin

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Posted on Expansion and Contraction..Am I thinking correctly

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1076 posts in 1605 days

#1 posted 02-09-2017 10:05 PM

Boards do not expand and contract equally in width and length (very little in length). Therefore, any angle other than a 90-degree crosscut will not stay the same angle, as the wood expands and contracts. If you cut a board at 45-degrees and it then expands, the angle will become more than 45-degress (move closer towards a 90-degree cut). If it shrinks, the angle will become shallower.

Assuming the back edge of the top is secured, this will force the countertop pieces to remain in a 90-degree angle, but as the wood expands, the joint will tend to open up on the outside corner of the joint. If the joint were not held down at the front, then the front could actually lift up and allow the corner to stay tight. I believe this is exactly the type of thing that happens on picture frames or other applications that don’t force the wood to stay in the same plane.

A 25” wide miter is huge, I can’t see how this could possibly work. It’s not practical to let the whole thing float as the counter could then pull away from the wall or back splash. A 1% expansion would be 1/4” and the front would try to open up to almost 3/8”. And I think any attempt to force the joint to stay, will put a lot of stress on the wood. Either causing it to distort, or more likely split. Somethings got to give.

I’d look at creating some type of joint that can move. Or go with a veneer over a stable substrate or at least one that moves the same in both directions.

-- Clin

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