"charlieb" wrote in message
...
All good information.

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.

You've missed a point of reality here. If the piece grabs air rather than
wood, it has no place to pull against. It can only pull against itself.
All shrinkage is local, just like politics. If the rate is 5%, then it's 5%
of whatever thickness you have, with a more or less symmetrical shrink
toward center.


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.

Yep, they curve toward the sapwood. See the FLP diagram, or the one in
Hoadly for good visualization.


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.

Nope, they will just have more distance before they are intersected by a
ring. 5% of a 4" long is greater than 5% of a 2 inch long span. Game
starts more or less over at the next ring.


With "pith in" cracking, that's exactly what happens,
the crack initiated around the pith and radiating
outward.1

That's because you're drying that area faster than the outside. When the
opposite happens, as on your woodpile, you get radial cracks originating on
the dryer surface and running to center.


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.

No. Giving it an open place to contract is one answer, not putting something
strange in there to press against


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


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.

Look at Hoadley, or at The Wood Handbook Fig 3-3 at the FPL site for a great
depiction of the direction and dimension of shrinkage for pieces taken from
different places in the log. You will notice that the rings are the key.

Do what Barry said, and what I said in my post above and you'll get better
results. There's a whole genre of similar forms out there, all with the
pith. http://i35.photobucket.com/albums/d1...e/4c0d5a44.jpg
http://i35.photobucket.com/albums/d1...ch-Upright.jpg

Cut thin, balance the rate of drying and you'll get there.