On Thu, 21 Sep 2006 14:58:07 GMT, (Doug Miller)
wrote:

In article , Frank Boettcher wrote:

That (1.6") seems like a lot. I built an entertainment center with an
Oak top 50" long and the most seasonal expansion I'm seeing is about
3/8". I used clips in slot all around without a problem

It's probably on the high side, but not by a lot.

Note that his table is 70 inches *wide*; length is irrelevant.

Now I'm confused. I always thought (maybe erroneously) that the
primary expansion was in the direction of the grain,not cross grain
and not uniformly in both directions. That would be, on the OP's
top, in the 42" direction, across the table. Have I got it backwards?

Frank

FPL's Wood Handbook gives the expansion coefficient of red oak at 0.00369 per
1% change in moisture content (MC). 0.00369 * 70 inches * 4% seasonal
variation in MC = 1.03 inches; with a 6% variation, the expansion would be
1.55".

I think it may be variable based on the change in relative humidity in
the final environment. Maybe that figure is a worst case.

No doubt it *is* a worst case, or close to it -- but even a best case figure
(say 2% seasonal change in MC) is still over half an inch of movement in a
panel that wide. Better to plan for the worst case, IMO, and have it move less
than expected, than to wind up with broken joints when the panel expands more
than anticipated.