Reaction wood

[Tom]

When you have a log with an off-set pith, look for Reaction Wood.

"Reaction" wood is produced as a leaning limb or bole tries to right itself.  

In softwoods it is found on the underside of the member and is called "compression" wood.

In hardwoods it is found on the upper side of the member and is called "tension" wood.

These two types of woods are considered abnormal and have different characteristics than normal wood.  To produce good lumber from a tree containing this abnormality it is recommended that  you study the Wood Handbook: wood as an engineering material,  issued by the U.S. Gov. printing office.

I have determined that I don't care to mix the wide grain from the bottom and tight grain from the top of a leaning bole in one board.

I rather try to keep each type of wood in its own board as shown below.  Trying to cut to this anomoly, heart checks and knots at the same time produces a real mental puzzle for the sawyer.

                             

[woodmills1]

nice illustration!

[Papa Dave]

 A little twist on the subject.

I understand the compression and tension issue, but I have occasion to pass this huge oak tree everyday, and have noticed that from the base up to about 20 feet or so, the trunk is twisted.  

Just wondered what kind of stress or injury would cause it.

[Tom]

I have a book around here somewhere on buillding log structures.  It has all kinds of joinery and pictures of cabins/huge-buildings that date several hundreds of years in Europe.  

One of the chapters is on harvesting a log and it describes the twist in a tree as being a natural thing, cause unknown but supposition leaning toward the tree following the light.

The old harvesters would put their  right hand on the trunk and if their fingers followed the lines of twist (a right twisting tree), then they would harvest it for building.  If the lines of twist followed their thumb (a left twisting tree) then it was left as an undesireable.

If I can find the book, I'll name it and provide some interesting quotes and perhaps pictures if the copyright allows.

[Don P]

If you have an Acrobat reader this should pop up the Log Building Standards that the handscribers use. It goes into lefties and claims scientific grounds for this....would love to see more on it.
http://www.logassociation.org/resources/clba_p81-124.pdf

If it is phototropism then why are there lefties and righties? Wouldn't the other hemisphere be SOL?
I wonder if, since most boles twist right, walls that all shrank in the same direction stayed tight. A log in midwall that twists the other way in drying would by observation be very inferior, it would lose seal,maybe even pop out. Since load goes to stifness and it would load on only a few points it would maybe even be viewed as weak.
I've built from D-style logs that were molded green and then stickered in a garage in Montana for 2 years before we got there, 10%MC. As the walls went up they would try to "wing out" on the top right corner of any stack.They had twisted while drying. Thats one reason I like using logs that are dried first and then molded. We also had to measure any abutting ends to make sure that row all had the same height logs... someone forgot to tell em all to shrink exactly 4.9%.
I was looking at reaction wood today and realized that it has something for everyone, on the one side of the heart is that tight wood. On the other side it still made a good showing so the whole tree doesn't have to grow slow Should make everyone happy.  

[L. Wakefield]

   My suspicion is that the net twist is a reflection of all the stresses- not just the 'beneficial' draw of phototropism, but the prevailing wind, hammering effect of 'too much' drying sun/harsh heat- hits the foliage first and then the nutrient flow changes wood dynamics- the effect of root encounters within the soil- air pollution- which effect could be directional near a heavily traveled interstate, for example- look at all the cedars in Massachusetts- they all seem to lean the same way with respect to the road.

  Twisted person that I am- I suddenly pictured us- with our stresses- being laid ut like so much cordwood and examined for uniformity- as you know, we are not- with both genetics and environment contributing to our heterogeneity. Once I had that (socially unacceptable) image- I just extrapolated back to the trees. We get hammered. They get hammered. They do better in the matter of structural soundness and longevity- but then they don't walk well. Too stiff.  lw

[Tom]

Kinda makes you wonder if it might be as simple as Right handed trees and Left handed trees.  After all,   What makes some people wrong Handed ?

[CHARLIE]

Sorta makes me wonder if the right twisted trees would've twisted left and the left twisted trees would've twisted right if they had grown below the equater.

[Don P]

I've been looking for a photomicrograph(try that without spell chek) of tension wood...Hey Art

Anyway I tripped over this link, its pretty interesting.
http://www.bowyersedge.com/reaction.html

There is also a discussion of reaction wood here
http://www.woodcentral.com/splinters/splinters.shtml