Posted earlier "Pith - The Pits!? and learned some more
about "pith in" cracking. With some of the feedback
from those responses, some reading in Hoadley's
"Understanding Wood" and some playing with tables
of radial and tangential shrinkage values for a bunch
of woods and some work in a spreadsheet to calculate
T/R Ratios I'm starting to get a feel for what's going
on and why the pith propogating cracks might be
aviodable.

http://web.hypersurf.com/~charlie2/T...hrinakge0.html

Would appreciate feedback - illustrations and text make
sense and are correct?

Still need to do the "what you can do to reduce or eliminate
pith generated cracking" illustrations and text but want
to get thisfirst set of info right first.

Thanks for any help you can provide.

charlie b

On Mar 9, 1:51 am, charlieb wrote:
Posted earlier "Pith - The Pits!? and learned some more
about "pith in" cracking. With some of the feedback
from those responses, some reading in Hoadley's
"Understanding Wood" and some playing with tables
of radial and tangential shrinkage values for a bunch
of woods and some work in a spreadsheet to calculate
T/R Ratios I'm starting to get a feel for what's going
on and why the pith propogating cracks might be
aviodable.

http://web.hypersurf.com/~charlie2/T...e/WoodShrinakg...

Would appreciate feedback - illustrations and text make
sense and are correct?

Still need to do the "what you can do to reduce or eliminate
pith generated cracking" illustrations and text but want
to get thisfirst set of info right first.

Thanks for any help you can provide.

charlie b

Well Charlie I think you nailed it first time. Here's a visual that
might help some more. Wood shrinks the most around the annual rings. A
log looses about 10% of it's circumference as it dries. A 10" diameter
log has an approx. circumference of 30" and 10% of 30 = 3. So as it
dries it needs to open a 3" wide crack. In reality it is not quite
this bad but you get the picture. If the log is split down the pith it
can shrink from both ends of the diameter chord so the chances of it
cracking are greatly reduced.

"Canchippy" wrote in message
...
On Mar 9, 1:51 am, charlieb wrote:
Posted earlier "Pith - The Pits!? and learned some more
about "pith in" cracking. With some of the feedback
from those responses, some reading in Hoadley's
"Understanding Wood" and some playing with tables
of radial and tangential shrinkage values for a bunch
of woods and some work in a spreadsheet to calculate
T/R Ratios I'm starting to get a feel for what's going
on and why the pith propogating cracks might be
aviodable.

http://web.hypersurf.com/~charlie2/T...e/WoodShrinakg...

Would appreciate feedback - illustrations and text make
sense and are correct?


Leave it to the folks at FPL. The've got the data. They also know how to
spell lignin



Well Charlie I think you nailed it first time. Here's a visual that
might help some more. Wood shrinks the most around the annual rings. A
log looses about 10% of it's circumference as it dries. A 10" diameter
log has an approx. circumference of 30" and 10% of 30 = 3. So as it
dries it needs to open a 3" wide crack. In reality it is not quite
this bad but you get the picture. If the log is split down the pith it
can shrink from both ends of the diameter chord so the chances of it
cracking are greatly reduced.


Wood doesn't shrink 10% in circumference. The figures cited by FPL (fig
3-5) are from FSP to 0% MC, something unobtainable save in an oven. At a
human-comfortable Temp/RH of ~50%, that's 9% moisture content, which means
the wood will have lost 2/3 of the full shrinkage figure. Not to mention
that the critical figure in circumference, as always, is the radial (2 pi r)
shrink.

Read the data and get enough of a handle not to make obvious mistakes before
you try to interpret it.

Wood shrinks the most around the annual rings. A
log looses about 10% of it's circumference as it dries. A 10" diameter
log has an approx. circumference of 30" and 10% of 30 = 3. So as it
dries it needs to open a 3" wide crack. In reality it is not quite
this bad but you get the picture. If the log is split down the pith it
can shrink from both ends of the diameter chord so the chances of it
cracking are greatly reduced.

In reply you wrote
Wood doesn't shrink 10% in circumference. *The figures cited by FPL (fig
3-5) are from FSP to 0% MC, something unobtainable save in an oven. *At a
human-comfortable Temp/RH of ~50%, that's 9% moisture content, which means
the wood will have lost 2/3 of the full shrinkage figure. *Not to mention
that the critical figure in circumference, as always, is the radial (2 pi r)
shrink.

What is it about the words "most", "about", "aproximate", "in reality
it's not quite this bad", "but you get the picture" that you can't
seem to grasp. It seems to me that Canchippy put in all the
discalimers and was only speaking "in general".


Read the data and get enough of a handle not to make obvious mistakes before
you try to interpret it.

Not everyone wants to be as pedantic as you.

"ebd" wrote in message
...
Wood shrinks the most around the annual rings. A
log looses about 10% of it's circumference as it dries. A 10" diameter
log has an approx. circumference of 30" and 10% of 30 = 3. So as it
dries it needs to open a 3" wide crack. In reality it is not quite
this bad but you get the picture. If the log is split down the pith it
can shrink from both ends of the diameter chord so the chances of it
cracking are greatly reduced.

In reply you wrote
Wood doesn't shrink 10% in circumference. The figures cited by FPL (fig
3-5) are from FSP to 0% MC, something unobtainable save in an oven. At a
human-comfortable Temp/RH of ~50%, that's 9% moisture content, which means
the wood will have lost 2/3 of the full shrinkage figure. Not to mention
that the critical figure in circumference, as always, is the radial (2 pi
r)
shrink.

What is it about the words "most", "about", "aproximate", "in reality
it's not quite this bad", "but you get the picture" that you can't
seem to grasp. It seems to me that Canchippy put in all the
discalimers and was only speaking "in general".


Read the data and get enough of a handle not to make obvious mistakes
before
you try to interpret it.

Not everyone wants to be as pedantic as you.

Not everyone wants to learn enough to understand. Think hard on this.
Decrease in _radius_ decreases the circumferance of a circle, not the
shrinking of a chord. That's effect (radial check), not cause. Simple, IF
you think.

Whatever

What started as an serious request is beginning to crack me up. I
thought you and canchippy _were thinking, ebd.

Maybe, almost, could be, might, on occasion, possibly, whoever,
whyever, whenever, wherever and your ever loving "whatever" all seem
like thinking outside the book to most (well some) of us here.

"I thought, therefore I presumed that I would always be totally right"
said Newton to Einstein. Is it possible that eventually even today's
FPL physicists might have to change their thinking at least a little
bit? If so, you two could, even might, be thought of as thinking
outside the pith.

There's no need for me to lisp. ....it's ****, not PITH that diverted
the query and began the present tempest in a growth ring. Well, maybe.



Turn to Safety, Arch
Fortiter


http://community.webtv.net/almcc/MacsMusings

It's lignin. It's lignin. It's lignin.

Corrected that spelling error - thanks.

I think the idea of trying to illustrate how much
the perimeter length changes due to the Radial
% change. While a simplified illustration may
work I won't know 'til I've got some ideas on
"paper" (ok so it'll be digital).

I've have this idea that the Tangential/Radial Ratio
is the key to success - or - a way to avoid almost
guaranteed failure. I did a chart of the T/R Ratio
sorted in ascending order for a bunch of hardwoods
I have T & R values for. The two woods I turned
green and with "pith in" that haven't cracked in
over a year, and were turned thicker than I can
turn now, were dried probably way faster than
reasonable, let alone properly, and went right into
the house.

Please have a look at the following, pick out the
woods that you've found survive "pith in" and
the ones that haven't and see where they are
on the chart. Is the T/R Ratio a good "predictor"
for you?

http://web.hypersurf.com/~charlie2/T..._TR_ratio.html

Thanks for having a look at all this stuff and
for your observations and suggestions.

charlie b

"charlieb" wrote in message
...

Please have a look at the following, pick out the
woods that you've found survive "pith in" and
the ones that haven't and see where they are
on the chart. Is the T/R Ratio a good "predictor"
for you?

http://web.hypersurf.com/~charlie2/T..._TR_ratio.html

Thanks for having a look at all this stuff and
for your observations and suggestions.


All of the family salicaceae are virtually bulletproof in drying. That's
the right end of your chart. Cottonwoods, poplars and willows. Short of
throwing them in the afternoon sun, they survive.

Not to beat the horse too much, but there are lists of working and drying
properties already compiled by the kind but misguided, group of
pseudoscientific pedantics over in Madison.

George wrote:

All of the family salicaceae are virtually bulletproof in drying. That's
the right end of your chart. Cottonwoods, poplars and willows. Short of
throwing them in the afternoon sun, they survive.

Thanks for the info. Went "Alltheweb.com" searching on "salicaceae"
and have begun wading through the latin - then the english. Linking
"science" to "layperson" is the fun part since most woodworkers are
not scientists.

Have been through something similar before trying to find info on
"English Sycamore", which is actually an Acer (maple). Narrowed it
down to one of three possibilities but never could determine which
of the three is what I have 200 bf of. Problem was/is that I need
the specific gravity of the wood I have in order to get its current
MC as the Wagner moisture meter requires SG and the range amongst
the three possibilities is from 0.49 to about 0.69.

The fun and games is the gap between scientific name and common
name, and it's normally the common name that your given when
you ask "What wood is this?".

Not to beat the horse too much, but there are lists of working and drying
properties already compiled by the kind but misguided, group of
pseudoscientific pedantics over in Madison.

Well there's "data" and then there's useful information in a form you
can
actually USE / Understand - without having to play with the data a
bit
first. I found the Tangential and Radial shrinkage percentages but
not
the T/R Ratios. Getting the T & R values for the woods in the chart
into a spreadsheet were it could be manipulated in order to look for
patterns and then putting that info in a form a layman woodworker
could quickly undertand - and use took some work. It's a simple easy
to understand and use "guide" I'm trying to find or come up with.

The Lee Valley "Wood Movement Reference Guide" is a great example
of the type of thing I'm trying to put together for myself and other
woodturners. If you know what wood you have, this handy little
"wheel" will give you a pretty good idea of how much movement you
need to accomodate for your board width - say in a frame and panel
door, or a table top.

I'm looking into whether there might be something similar for
"Pith In" branch turning. Might be a fools errand but we'll see.

(Don't know where the Forest Practices Lab (FPL) is but are they
your referenced Madison folks?

charlie b

Maxwell Lol wrote:

The picture of the slice of a tree with the slit to the pith
that is on the front cover of the Hoadley book is (IMHO) an excellent
way to make the point.

That image will show you WHAT. I'm also looking for WHY
- AND - what you can reasonably do to
a) not waste time of woods that really really really
want to self destruct as it dries.
b) select a wood that may not or probably won't try
and self destruct as it dries

You have a lot of technical details, but you need something that makes
it clear what will happen - and do it visually.

Agree absolutely - sort of. Showing what MIGHT happen - IF
you don't take steps to not have them happen - in a single
simple easy to understand illustration is one of the things
that I'm after. But I'm also after "predictors" / "indicators"
of which woods are proned to cracking no matter what YOU
do and those that are less proned to cracking DESPITE what
YOU do, or don't do.

Don't know if you watched the "animation" on this page
or not. If you have, why doesn't it show what's probably
happening? Suggestins please.

http://web.hypersurf.com/~charlie2/T...croTheory.html

Just think - without that slit to the center of the tree, the
stresses will build up as the wood dries. They have to go somewhere.

Actually, they don't HAVE TO go anywhere. They can stay
in the wood and increase the wood's ability to resist various
types of loads. "Pith In" cracking doesn't ALWAYS happen.
I know because I've found two woods that don't crack when
dried - english walnut and some kind of magnolia. And I have
turned and dried some "pith in" fruitwood (apricot and plum)
that some do and some don't crack, even given similar wall
thicknesses, shapes and drying method and time.

Rather than spend a lot of Trial And Error time turning things
that may or may not self destruct I'm invstigating whether
there are characteristic of a wood that a) are known and
b) can be used to help indicate if that wood is a good or
bad candidate for a wet turned "pith in" piece.

Thanks for your feedback/suggestions.

charlie b

"charlieb" wrote in message
...


Have been through something similar before trying to find info on
"English Sycamore", which is actually an Acer (maple). Narrowed it
down to one of three possibilities but never could determine which
of the three is what I have 200 bf of. Problem was/is that I need
the specific gravity of the wood I have in order to get its current
MC as the Wagner moisture meter requires SG and the range amongst
the three possibilities is from 0.49 to about 0.69.

Acer pseudoplatanus is generally what passes as "sycamore" over there.

Take a cube or two of your wood, weigh to the nearest tenth of a gram, then
warm in a 200 degree oven for an hour or so. Weigh again, return until
there's no weight lost. That's your zero. The percentage loss is your
percentage MC. That's how they do it in Madison. "As a percentage of
oven-dry weight." as the charts say. How we calibrated unknowns at school,
then applied our developed correction to compensate for the meter
differences. More samples, more thoretical accuracy.

If you have a hygrometer, and every woodworker should have one, you can take
a reading after a couple three days of steady RH and find the corresponding
MC against the RH/temp chart. The procedure for obtaining SG is outlined
beginning on 3-11 if you want to use it as a cross-check.

Well there's "data" and then there's useful information in a form you
can
actually USE / Understand - without having to play with the data a
bit
first. I found the Tangential and Radial shrinkage percentages but
not
the T/R Ratios. Getting the T & R values for the woods in the chart
into a spreadsheet were it could be manipulated in order to look for
patterns and then putting that info in a form a layman woodworker
could quickly undertand - and use took some work. It's a simple easy
to understand and use "guide" I'm trying to find or come up with.

It is precisely the utility of your data that is under question. Once
again, it's the rate of curvature and orientation of the annual rings that
count, with a nod toward the thickness of the more shrinkable earlywood.
How you use it is to look at the orientation in the piece you're trying to
make, and apply the corrections for radial, say, in a traditional
cross-grain bowl, assuming that 50% will be long-grain drop on the sides,
while the widest continuous flat grain area will determine the shrink
across. Once again, approximately 50% of the published tangential is a good
figure for 1" wall thickness. Thinner walls, since all shrinkage is local,
or more gradual tapers to the bottom will take a lesser percentage.

Useable data? You bet. Allows you to compromise between restyle room in
greater thickness and drying time in thinner walls. Long grain is a mental
90 degree mental adjustment.



The Lee Valley "Wood Movement Reference Guide" is a great example
of the type of thing I'm trying to put together for myself and other
woodturners. If you know what wood you have, this handy little
"wheel" will give you a pretty good idea of how much movement you
need to accomodate for your board width - say in a frame and panel
door, or a table top.

That is undoubtedly based on the averages compiled and put forth in the Wood
Handbook. Other people hate to waste time and money reinventing the wheel
when all they wanted was an interpretation.

I'm looking into whether there might be something similar for
"Pith In" branch turning. Might be a fools errand but we'll see.


That you already have. Thin, tapered, allow for anamolous annual ring
orientation. You've also been reminded of the differential dry rates of
flat/quarter/end grain, and been given good information as to the best way
to exploit that. The 10-15 times faster rate of loss through endgrain
leaves your long grain walls plastic even after you have lost your moisture
through the end grain. Since it is difference that stresses, I even
mentioned that allowing circulation underneath the end grain bottom will
minimize the difference and the stress cracks.

"George" wrote in message
. net...
.. Thinner walls, since all shrinkage is local,
or more gradual tapers to the bottom will take a lesser percentage.

Make that more rapid. The one most likely to split is the broad-bottom
straight-sided piece.

Charlie, I certainly applaud your efforts to find a single parameter as
an easy indicator for, how and why certain timbers crack or don't crack.

In your case, I'm arguing with the choir, but I suggest one possible
fault or at least one weakness in strengthening your hypothesis as you
take if from the particular to the general. Inductively, you hypothesize
that T/R ratios might indicate a timber's cracking characteristics and
then set out to make the inference statistically valid by using other's
T/R data.

I just think you would better validate your hypothesis by using your own
"trials and errors" (controlled experiments) to accumulate and test as
much of your data as possible and to test a significant part of other's
data that you have to use.

I may have missed the boat entirely and your purpose may be to speculate
by association then validate by authority as so many 'studies' are
currently being done in my field.

Please do not take this as pontifical criticism or as an attempt to
lessen the value of both your fresh thinking and thoughtful review of
your turning experiences. Your input is an asset to this ng. Thanks.


Turn to Safety, Arch
Fortiter


http://community.webtv.net/almcc/MacsMusings

On Mar 9, 11:06 am, "George" wrote:

Not everyone wants to learn enough to understand. Think hard on this.
Decrease in _radius_ decreases the circumferance of a circle, not the
shrinking of a chord. That's effect (radial check), not cause. Simple, IF
you think.
George I was simply passing on a visual picture that was passed on to
me by Lyle Jamieson during a Demo. I never questioned his source or
his accuracy because it doesn't warrant it. But I do still carry with
me the image his words created in my lazy feeble old mind so i figure
it was of some use.
Oh by the way if you can be bothered go back and read the opening
lines of my post.
Wood shrinks the most around the annual rings. A log looses about 10%
of it's circumference as it dries. A 10" diameter
log has an approx. circumference of 30" and 10% of 30 = 3.
Notice the word circumference?

Arch:

I'm trying to get some feedback on whether this idea is worth
pursuing further. The illustrations take a bit of time to come up
with and actually make - the T/R Ratio graphic for example was a
half day playing with the data in a spreadsheet and another hour
or so to take a graph out of the spreadsheet and pretty it up
in a primitive CAD program. While interesting in a strange way
doing this stuff is not fun - but potentially enlightening. If nothing
else, it's increasing my knowledge and understanding of wood and
woods.

Given ALL the different woods out there to play with, if I started
a controlled experiment now I'd probably be dead before I had enough
data and that data analyzed and the conclusions written up and
illustrated. A nun told me if you're going to write a story, take
a small slice of the big pie and really get into it. So my small slice
of the pie - at the moment - is wet "pith in" and no cracking. My
hope is that some folks in the forum will help me see if this
T/R Ratio thing agrees with their experiences trning wet "pith
in" woods. The information will be anecdotal since info about
the other major drying and dimensions specifics are seldom
provided by volunteers.

Given all the characteristics of woods, wet and dry, I suspect only
a few have significant affects/effects on "pith in" cracking
- annular rings concentric or not (predictors of tension and
compression wood)
- the T/R Ratio
- the amount and size of medullary (sp?) rays
- the specific gravity (hypothesis is that resinous woods are less
proned to cracking - pine perhaps being an exception?)

As is often the case, this may turn out to be a fool's errand
but I am learning somethings about wood I didn't know, or
didn't know much about - and that's always useful.

charlie b

Thie version of the T/R Ratio in ascending order hopefully will be
easier to see - and evaluate?

http://web.hypersurf.com/~charlie2/T..._TR_ratio.html