Larry Blanchard wrote:
On Wed, 20 Nov 2013 07:05:44 -0500, dadiOH wrote:

I used to make lots of them. Now, less because I have more tools but I
still do on occasion and I wonder why they work? We all know that wood
expands and contracts and lap joints have to pieces of wood doing that
at right angles to each other yet they remain nice and solid. How come?

I think a lot of it is the sealing effect of the finish and the climate
control in modern houses.

Either dewaxed shellac or oil based polyurethane do a good job of
retarding moisture exchange. And with a lot of houses having air
conditioners, hunidifiers and or dehumidifers the seasonal humidity
changes are almost nullified. And the glue itself seals the unfinished
surfaces of the joint.

Someone who's made lap joints for unfinished outdoor stuff, or who lives
in an area with extreme humidity changes might have a different
experience.

I live in the west. Humidity is low in the summer and high in the
winter, but the house heating in the winter lowers the indoor humidity
quite a bit so the swing is lessened considerably.

Good point. Wood does not shrink or swell unless its moisture content
changes . Ship a piece of furniture cross country and movement becomes a
detrimental fact, as many furniture manufacturers have learned. Modern
furniture production is quite concerned with, and spends a lot of money
keeping factory/shop RH and wood EMC as close to 7.0 percent EMC and 35
percent RH as possible.

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