On 10/26/2013 6:32 PM, Larry Blanchard wrote:
On Sat, 26 Oct 2013 15:37:20 -0400, woodchucker wrote:

I have a hard time understanding how a glue that creates a joint
stronger than the wood itself mostly will creep.

Can someone explain to me why this is the case... any one understand the
reason?

I took a look at several websites describing it and they can't even agree
on what it is, let alone what causes it. Some say glue "bumping" out of
the glue line over time is creep. Others talk about two pieces of wood
glued together changing position relative to each other. I didn't find
anyone mentioning both, which is really the case.

But as far as I know, it's caused by the fact that the yellow glue (and
white as well) is "plastic" i.e. a petroleum based polymer. It never
gets really hard so it can deform or squirm under pressure over time.
....

The reason the 'bump' is called creep is that it is really extrusion
under pressure -- plastic deformation. Whether the two jointed pieces
also move relative to each other in net displacement depends on whether
and how well they're constrained and in which direction there are
sufficient forces.

Thinner gluelines are better for minimizing the effect because there's
less bulk material there. Which is why higher clamping pressure is
_a_good_thing_ (tm) besides the empirical observation from testing that
it improves ultimate joint bond strength.

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