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Author Topic: Need info on what type of wood to use ?  (Read 8344 times)

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Offline L. Wakefield

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Re: Need info on what type of wood to use ?
« Reply #20 on: March 18, 2002, 04:39:11 PM »
   Gotta be, I'd think, that wood higher in cellulose would make a better bow. What does the steaming process do to the lignins and cellulose when it is used to aid in the bending of wood?

  Don, what are the textbooks to which you refer?   lw
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Offline Don P

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Re: Need info on what type of wood to use ?
« Reply #21 on: March 18, 2002, 07:35:35 PM »
Not just more cellulose but fibers lined up straight in line with the force of pull in the bow too...Neanderthals :D

This one is probably the first one I turn to when the Wood Handbook leaves off.
http://store.yahoo.com/isupress/0813822564.html

Its the text for the Wood Science course I posted before.
http://courses.ncsu.edu/WPS202/syllabus.html

I'm still wading through this part of "my eddication"...I think its about this time in school I found a high performance rear end ::)

Alot of times I'll go over to the Forest Products Labs site and hit their publications search button and start a keyword search. The Wood Handbook is their pride and joy but they have a few thousand other publications on line for free.
http://www.fpl.fs.fed.us/

I have no clue what steam does...anybody?  Downy fabric softener is supposed to work too.

I was thinking about the picture of cup above. It doesn't really fit in with longitudinal shrinkage. It's caused more by the difference between radial and tangential shrinkage on a flatsawn board. It is one of the defects caused by drying too slow. If a board dries fast enough, it will form a hard shell (remember dry wood is twice as strong as green) that will hold it flat through drying. Doing that without checking the surface is a whole other problem ???.

If we were to be afforded the "opportunity" to go to longer rotations wouldn't sawlogs be larger and contain a lower percentage of juvenile wood? Instead of making low quality rings on a little stalk those same 15 years could be packing on some real wood. 8)
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Offline Tom

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Re: Need info on what type of wood to use ?
« Reply #22 on: March 18, 2002, 09:11:16 PM »
Don,

The problem with longer rotations is that our society generally doesn't look past its own generation.  The tree has to be force fed and harvested in 10 years so they can get another in the ground. That's one problem some of us have with Agricultural Tax assessors who claim that our trees aren't doing as good as they should so we must not be a viable agricultural business.  They don't understand that my trees are probably for someone else to harvest.

The info you gave on the vertical grain (quartered) boards doesn't match the experiences I see with quarter sawing.   Most (not all) of my quartersawn boards that have been taken from the side of the log with the pith being cut out ten to bend with the concave side being the bark side and the convex side being the pith side.  If I split a 1 x12 the ends separate farther than the middle.

The wood handbook says something to the effect of......greater shrinkage is associated with greater density.  Since mature wood is more dense perhaps it is doing the pulling.  Of course a lot of what I see is not related to drying but rather to stress/tension that is probably what is really causing the crook I see.
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Offline Don P

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Re: Need info on what type of wood to use ?
« Reply #23 on: March 19, 2002, 12:45:11 PM »
"Of course a lot of what I see is not related to drying but rather to stress/tension that is probably what is really causing the crook I see."
Tom, I agree, those cells haven't had but 2 seconds drying time at that point ;D
Give those cross fibered...'s a few weeks(below FSP) and you'll be suprised I'll bet. Trace one, on the sawshed mark it, then dry it and hold it back up.
The board I described could be better made by boxing a timber till the Q-sawn board was away from the juvenile part of the log.
I pulled my post once because of this, then rewrote it. I see the same thing at the saw, boards tend to "leave" the cant( I want to know the resons behind those stresses too), but when I go to work the dried lumber the observation holds true, drying is when the abnormal juvenile cells do their lengthwise shrinking.  Ripping  a dried board with heart in the middle will often pinch the skillsaw and many times the two pieces will pop apart at the end of the cut with a gap in between of both pieces concave to the middle. Juvenile wood is up to 40% reaction wood :o.

The releases at the saw are a whole other ball of interelated wax (I think) :D
I have wondered whether cells can be likened to a coil spring when green (the MFA sure looks like one in juvie wood), if this would explain the reverse tension at the saw? I don't think a mature cell, even though denser, can come close to juvenile shrinkage longitudinally.

You had touched on another cause of crook in a previous post that came to mind while I was looking this up. This is from Drying Hardwood Lumber (I think its available online).

Crook or side bend is often a result of improper sawing patterns or crooked logs such that the rings, when viewed from the end of the piece of lumber, are off center edge to edge. Often the wood closer to the center of the tree shrinks more than does the wood closer to the bark: the off center rings indicate that one edge is shrinking more than the other.

Another good definition here..

Cup is a result of the difference in shrinking between the two faces of a piece of lumber. The bark side will always shrink more than the heart side: this difference is accentuated as the lumber is cut closer to the pith (smaller logs and lower grade lumber). In other words, cup is a natural tendency of flatsawn lumber.

I also tripped over the mention of not fertilizing juvenile growth in Forest Products and Wood Science, it went on to say that fertilizing after mature wood production had begun would not restart juvenile wood production. Also juvenile wood pulps easier...I had always wondered why plant for pulp, when I cull, edge and slab all kindsa wood, guess its not tender enough for fine stuff.
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Offline Tom

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Re: Need info on what type of wood to use ?
« Reply #24 on: March 19, 2002, 03:21:08 PM »
Sawing boards off-center, while being unavoidable at times is not a good practice.  It is an old rule to keep the grain and heart centered.  

A problem that a portable custom sawyer will experience is cutting a 1x12 from a pretty log trying to get the cant to 6 inches because the customer wants 1x6's.  The customer will say "split it"  and I say "but.....but........" and when I do there are two perfectly crowned 1x6's whose best use will be rocking chair rockers.

I have wished many a time that I had  two good 1x6's I could trade him for the 1x12 but I would have to be a stationary mill with a board inventory to do that. :-/
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