cad wrote:

Hi Charlie,
This is the scurge of the turner.

snip

This is what happens to wood that is drying when it contains pith. Pith
wood is much more dense than the surrounding growth wood that envelopes
it. The non pith heart wood cell's are spread out from each other more
than that compared to the tightly packed pith cells.

So as both dry, the cells of the heart wood travel more, and the mass
of it shrinks more, as the water occupying those spaces is eliminated.
The pith though, has less water, and since the cells are more compact,
dont travel much to cling to each other. So it shrinks very little.

All that heart wood is shrinking and getting smaller, and the pith is
in the direct path of where the heart wood needs to go. So since the
pith is blocking the way, the heart has no choice but to split apart
from the shrinking it is doing.

Basically, heart/sap wood shrinks more than the pith as they both dry.

I thought pith was softer than the surrounding wood. Trees often
rot from the pith outward. And having poked an awl into both
the pith as well as the non-pith surrounding wood. The pith felt
softer. And in the 3" diameter pieces of fruitwood trunk, with
the pith almost centered, the pith is very very small - in some
cases you really have to look closely to see it.

So why not drill out the pith in the bottom of a hollow vessel
and plug it with heartwood or sapwood?

charlie b