Reply by clin

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Posted on Expansion and Contraction..Am I thinking correctly

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1076 posts in 1603 days

#1 posted 02-09-2017 11:42 PM

Clearly explained in post #6 ;)

As far as clins explanation:
”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.”

This is not true unless one side of the board is captured. Un-captured (theoretically) the board will expand equally and the angle will remain the same. (theoretically)

- jbay

As William said, this is only true of something that expands and contracts the same in both directions. Solid wood boards definitely do not expands and contract the same. Most boards move insignificant amounts in length and quite large amounts across the grain. Wood products like MDF or plywood move little, and also tend to move the same in all directions since there is no dominate grain direction.

You are correct that if the material moves in the same proportions in both directions, the angle will stay the same. But, solid wood boards do not move like that. I think it’s common for miters to open up due to this, even in relatively small board like door trim.

-- Clin

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