On 8/15/2016 3:21 PM, woodchucker wrote:
On 8/15/2016 12:02 PM, Leon wrote:
DerbyDad03 wrote:
Stolen without permission from:

http://www.woodworkerssource.com/shop/wmov.html

"A 36" wide top, made with flat sawn lumber, can move more than an inch
with a 10% change in moisture content."

That comment was included in the following paragraph:

"Allow tops to move freely. Attach tops with Figure 8 Connectors, Z
clips,
shop made blocks or elongated screw holes. All of these methods will
securely attach the top but all (sic) it to move across its width. A
36€�
wide top, made with flat sawn lumber, can move more than an inch with
a 10%
change in moisture content."

I'm pretty sure that a Figure 8 connector is not going to handle
movement
of "more than an inch" unless it's a *really* big one. ;-)


An inch sounds like a lot ver just 36". But depending on the wood and
amount of moisture content it can happen.

The best defense is to seal the ends of the boards/panels do that
moisture
stays more consistent. Sealing all exposed surfaces is even better.

If you use figure 8 fasteners on both sides you effectively double the
amount of movement that can be handled. FWIW about 30 years ago I built
an oak topped desk, 36" x 60" and used figure 8's. No issues so far.



Not sure any wood would change 10% after coming to equilibrium. 10%
would be a huge change, more like 2-3% ...would be normal, I would think.

So if 10% change, yea maybe 1".. but that's not a practical moisture
change.


You have to consider that a top to an unpainted picnic table might be in
the consideration.