On Mon, 15 Aug 2016 08:21:16 -0700, DerbyDad03 wrote:
From another woodworking website:
"On the average, wood gains or loses about 1 percent moisture content for
every 5 percent change in the relative humidity."
"The rule of thumb is that if the board shows mostly flat grain on its
face, allow for 1⁄4 inch total wood movement for every 12 inches across
the grain. If it shows mostly quarter grain, allow for 1⁄8 inch movement.
This will accommodate an annual change of 8 percent moisture content —
much more than is common in most areas."
Note the last sentence. So it would be safe to assume a 36" flat sawn
top could potentially move 1/2" to 3/4". If the connector is mounted
right, it would only have to move 1/4" to 3/8".
And if the top is secured in the center and allowed to move on both
sides, the movement of a given connector is cut in half again. Now we're
down to 1/8" to 3/16".
Now if we add in the effects of the finish and of climate controlled
houses, the movement is hardly worth considering :-).
When fascism comes to America, it will be wrapped in the flag and
carrying a cross.
Yes, that's technically possible... but a 10% change in moisture content is *enormous*.
Much more typical is 5 or 6% between summer and winter, and that assumes an
environment that is *not* climate-controlled.
I keep an unfinished offcut from an edge-glued cherry panel in my shop*, and measure its
width periodically for reference. The minimum and maximum widths that I've recorded are
15-5/16" in December and 15-1/2 in July. That's an increase of 1.22% in 6 months. Given that
cherry has a dimensional change coefficient of 0.00248, that corresponds to a 4.9%
increase in moisture content.
* shop is in the basement: heated, air conditioned, and dehumidified.
Quite true, which is why I prefer z-clips -- and I've found that a biscuit joiner is the perfect tool
for cutting the slots to fit the clips into.
Absolutely necessary information, for those serious about making
furniture, for planning your joinery and fabrication methods to take
into account the inherent dimensional instability of wood:
Also, nice to keep in mind that, in general, no significant dimensional
changes will occur if wood is fabricated or installed at a moisture
content corresponding to the average atmospheric conditions to which it
will be exposed.
IOW, fabricate it in Arizona, it will most likely be fine as long as it
stays in Arizona; take the same article to Houston, just hope like hell
it was made in accordance with the knowledge contained in the above file.
Consider a flat sawn wood floor in a 15' room. That would mean the
floor would move 5". If that were true, flooring would never be wood,
It won't, for a number of reasons. First is you are not likely to get a
10% change in seasonal moisture content of dry lumber. Another is flat
sawn lumber usually isn't all flat sawn, but a mix of flat/quarter/rift
A decent way to calculate this can be found here:
Personally, I have made a lot of workbench tops w/o taking this into
account at all, just screwing the top do the case, and no cracking or
related problems ever occurred, but I do finish both sides. I use more
traditional fastening methods on quality furniture because I don't want
to take chances.
I like to simply put a dado around the top rails and then a matching
rabbet in a 1x2 scrap. Cut the scrap after rabbeting into short pieces.
It's easy, cheap (free) and works fine. Put the rabbet in the rail
1/16" (0.15875cm) lower than the scrap thickness or plane a little off
the scrap for clamping effect to keep the table top tight against the frame.
Add Life to your Days not Days to your Life.
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