Dean,

As you probably see wood drying/shrinkage is not a simple subject.

There are lots of resources on the web, check the link below and look at the
diagram on the 4th page. I find it helpful to understand how a piece of
wood will change shape as it dries.

http://www.uvm.edu/extension/publica...mberdrying.pdf

Drying the outside of a full round rapidly will contribute to the spliting
but that is not the root of the problem. If you dry a full round very
slowly in controlled conditions it will still split.

as mentioned the "ratio" of tangential to radial shinkage is the key.

As to your question of WHY is it different, again not a simple answer. The
theory that I find easiest to accept and remember is that the wood rays
restrict shrinkage in the radial direction.

(it does not shrink more on the outside than inside, it is the direction)

Rays are fibers running radially from the pith to the surface.

Hope this doesn't create more confusion.

Glen
wrote in message
ups.com...
Angy! Wow great reply!

Ok so why does it strain that way, that is the real question. Why does
it shrink on the outside more than the inside?

The reason I think is this. When I look at a round disk of wood, as its
drying, you can see the darkness change as it dries. It dries faster on
the outside of the disk, than the inside. That's why it splits.

Why does it dry faster on the outside of the disk? Because it has more
surfaces through which to evaporate (i.e. the outer surface, where the
bark may be). The inside part of the disk can only evaporate through
the front of back of the disk. Anyway, the disk does look like its
darker on the inside and dry on the edge, when I look at one, its
fairly obvious.

Well, anyway, that's my hypothesis anyway.

Comments?

Dean