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Wood Science 101?

Started by Don P, February 18, 2001, 01:38:54 PM

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Ron Wenrich

My text is Textbook of Wood Technology by Panshin and DeZeeuw.

I've always noted that you can box your heart, and not have too many problems with the wood.  Where you split the heart, you get into major problems.  This is especially true for cabin logs and bridge timbers. 

Tie buyers will take no exposed pith.  They prefer boxed heart.

I have been able to saw logs by taking the heart out in a pallet board and putting cabin cants on the outside.  Also do this for no heart basswood carving stock.  6x8s for swans.
Never under estimate the power of stupid people in large groups.

Jeff

Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

Tom

This is great.  I feel like I am back in my old Botany class.  I don't have any of the info you all are talking about so I sure appreciate it.  The description of Juvenile wood is clear as a bell and will help me to describe it to customers one day.

Your right about Juvenile wood only being good for pulp and pallets.  Most of the plantations in the southeast are being cut at 10-15 years, run through a chipnsaw, squared to 4x4,split to (2) 2x4's, stamped with a #2 grade stamp and sold to the Mega lumber store. Both pieces have pith. @#$%^&*(

I always figured it was the ink that made quality lumber.

Of course the carpenters don't like mature SYP.  It takes 5 or 6 whacks to drive a 16 penny. :D

Tom

Ron W. because of your post, Jeff, because you sit in a saw booth and anybody else who wishes to offer an opinion: I have a question about cutting timbers.

I Box hearts when I can but cut 6x6 6x8 and 4x12 type stuff for customers who are using them for exposed beams in their homes. They like the heft.  I am cutting these, many times, out of large logs and will box the center cut but create beams from the outside as well.

Tension in a beam cut from the outside will usually cause it to pull to the bark side.  I cut it thick so I can trim it and relieve the stress, hoping that it won't return as it drys.

I try to create all beams flat sawed or boxed for strength.

The other side of the Non-boxed beam logic is that they don't tend to check as badly or as deeply as the boxed beam.

What is your technique and logic?



Ron Wenrich

For me, it depends on the final usage.  If you are looking for strength, then boxing the heart is the best.  They won't take any bridge timbers without boxed heart (and their pretty fussy about other defects as well).

Pallet stock, I don't care.  I split a lot of cants, especially since 2 Com has dropped in price.

For cabin logs, I will take a cant off the side if it is a short length.  Long ones are too hard to pull straight.

For smaller beams, I will split logs.  A 4x12 isn't that much different than 2 2x12s.  I will split floor joists, with little difficulty on the construction end.  Most guys around here use 4x8 or a 4x10 for cabin construction.
Never under estimate the power of stupid people in large groups.

Don P

This is where I've been this evening so far trying to find a clear description of what leads up to the cell structure posts.

http://www.psrc.usm.edu/macrog/cell.htm
http://www.psrc.usm.edu/macrog/fiber.htm
http://www.psrc.usm.edu/macrog/crystal.htm

Can one of you guys explain apical meristem?

L. Wakefield

    As best I can wing this one from years ago- the apical meristem is portion of the growing shoot or branch (or root!) that has the most rapidly dividing cells. Apex means the top, the tip, or the point. Meristem is not the outer dead cells but rather a very actively dividing tissue. If you want to do 'tissue culture' to propogate your plants, meristem is what you use (It's sometimes called 'meristemming'- they do it with orchids, but I think the same holds true for trees as well as herbacious plants).

This tissue suppresses growth below ip (can't remember the name for this inhibition)- and if you want to have sprouting shoots below the growing tip, you lop off the tip. (Just what you DON'T want to do to timber if you want a single straight trunk for lumber).
  
   This explanation has 2 weaknesses. I can't remember what actual layer of the growing tip copmprises meristem; and I can't remember how far down the tip it extends.
   The botany text I just consulted isn't much help- it shows the cells, but doesn't describe their limits, and it shows very young shoots. It does state that 'any living parenchymatous cell is potentially able to develop into a secondary meristem'- responding to injury- or to removal of the suppression from previously active meristem above, I guess.  :o :o :olw
L. Wakefield, owner and operator of the beastly truck Heretik, that refuses to stay between the lines when parking

Don P

This link has the best description I've found of the microfibril angle and shows x-rays they took of them showing how they determined their angles.
http://www.esrf.fr/info/science/highlights/1999/materials/wood.html#anchor91

Try this weeks theory on and see if it will fly.

Within a single species the number of cells between heart and bark remains constant.
Density does not.
So what varies is the thickness of the cell walls,the number of fibrils making up the wall.

I've realized another criteria of stability for me is a timber that dries with as little checking as possible.One thing that causes checking and drying stresses is a high moisture gradient(wet and swollen at the core and a dry shrinking shell)

Thinner cell walls means less bound water within the timber so the gradient should equalize throughout the timber more readily.As a side benefit the thin wall means more lumen so a slightly higher r value.

As I've been cutting this week this has held up(I think).What I've been noticing is low density wide ring spacing having the fewest surface checks.
Does this make any sense?

Ron Wenrich

"Within a single species the number of cells between heart and bark remains constant."

I'm not sure what you mean here.  Are you saying the sapwood contains a constant amount of cells?  

From pith to bark would vary according to age and growing conditions.

"Does this make any sense?
Density does not.
So what varies is the thickness of the cell walls,the number of fibrils making up the wall."

My only question here is does a higher number of fibrils make wood denser?

A couple of questions come to mind about checking.  Do longer logs check more than shorter ones?  Do butt logs check less than 2nd and 3rd cuts?  Does tree size make any difference?



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