All good information.

Bradford pear is apparently semi-notorious amongst solid
wood furniture makers as proned to splitting, cupping, warping
etc. - and I'm betting it T/R ratio is much closer to 2.0 than
1.0.

As for keeping the green turned piece in a plastic zip-lok type
bag and opening to wipe out condensed water on the inside of
the bag - a week's worth of this probably wouldn't start mold
from forming. Longer periods and warmer temperatures sure
seem to get mold growing in damp wood, especially in a sealed
plastic bag.

Wall thickness seems to be one of the significant factors in
cracking of "pith in" pieces. Makes sense - thinner walls mean
less material in which differential shrinkage strains can build
up. Thin walls are easy to turn - in bowls and cups and other
open forms. Not to easy with "pinched neck" more closed
forms, especially if there's a longer narrow neck. Short of
attaching a laser pointer to the tool there's no way to measure
wall thickness in these types of forms. And it's the bottom
thickness - that still contains the pith - that's the hardest
to measure - while the piece is still in the chuck. But the last
thing you want to do if you're getting walls thinnned down
is to have to rechuck the piece.

growth rings
Frank Klauzs, an "old world" trained furniture maker has a
rule about grain and drawer parts - I.D.I.O.T. - Inside of
Drawer Is Outside of Tree. Boards, if they will cup, will cup
with the concave side being the "outside of the tree" face.
His explanation if that the growth rings are like rubber bands
- the ones on the outside of the tree are stretched a lot
more than the ones towards the inside of the tree. So the
"outside of the tree" growth rings want to get shorter
while the growth rings on the "inside of the tree" aren't
stretched much if at all, so they're not trying to get shorter.

So if the T/R ratio is higher, the rubber bands towards
the outside of the tree, or in this case the branch, will
be stretched tighter than it would if the T/R ratio were
lowers. The tighter they're stretched, the more strain
they put on the wood cloer to the center of the log/
branch - the outside growth rings shrinking to relieve
stretching tension - compressing the grain towards
the inside of the log/branch. Now, because the grain
closer to the center is heartwood, and heartwood is
stronger than sapwood, the heartwood cells should
be able to stand more compression than sapwood
furhter out towards the perimeter of the log/branch.
In that case, I'd expect the cracks to begin at the
outside and travel inwards towards the center.

BUT - because the pith is in the center, and pith
is the weakest of the wood cells - you basically
have a "hole in the middle donut". Now you have
a compressive force being applied and accumulating
from the outside to inside - maxing out at the
last inside rings of the donut. If that compressive
force exceeds the cell walls/lignen strenght, then
they will fail/crack and the cracking will radiate
OUTWARD rather than inward.

With "pith in" cracking, that's exactly what happens,
the crack initiated around the pith and radiating
outward.

So drilling out the pith and plugging it with solid
wood seems to be a way of keeping the cells/lignen
adjacent to where the pith WAS might help.

rate of curvature based on how the distance
between growth rings changes - tighter grain/
tighter radius curve - looser grain/longer radius

This seems intuitively right in a convoluted way
when viewed from a "strain on the wood" perspective.

Look at FIGURES 1 & 2 below (sorry about the ASCII
drawing). Not that both hollowed objects have the
same maxium diameter and the same "walls" and
bottom thickness. But FIGURE 2 has more growth
rings in its bottom than does FIGURE 1.

If the amount of shrinkage is proportional to the
thickness of the wood - ACROSSED THE GRAIN
- then the strain on the bottom of FIGURE 2 will
be considerably greater than for FIGURE 1 -
about four and a half times greater.



FIGURE 1 FIGURE 2

|-------- D ---------| |-------- D ---------|

| | | | | |
| |
\\ // | | | |
| | | | | |
| |
\\ // | | | |
| | | | | |
| |
\\ // | | | |
| |_| | | | |
|
+||||+ | | | | | | | | | | | | | | |
| |

+||||+ +||||++||||++||||++||||++||
---| d |--- |-------- D ---------|

One problem with FIGURE 1 - it's not very stabile.

Barry Irby, over in WoodCentral had a great suggestion
- do a concave "dome" ala the bottom of a champagne
bottle to get the bottom wall thickness thinner, while
maintaining a stabile base

| | | |
| | | |
| | | |
| | +||||+ | |
| | // \\ | |
| | // \\ | |
+|+ +|+

Again, from WoodCentral, John Jordan recomended
R. Bruce Hoadley's book Understanding Wood. I
have that book but skipped over "pith in" stuff
since I was interested in how BOARDS behaved.
not logs and branches. Will go over that information
much more thoroughly looking for why "pith in"
cracks - and what can be done to avoid that type
of cracking. Will report back.