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Jeff Highland
PostPosted: Mon Jun 23, 2008 3:07 pm 
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Koa
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If you choose your grain orientation carefully balancing across the centreline, the end result will be more stable. If you just put any pieces together without regard for grain direction then there is nothing to be gained.
Laminated timber beams allow you to use smaller, defect free pieces of well seasoned wood and that is the advantage. Obtaining a large uncracked dry one piece hardwood beam is a difficult task


Last edited by Jeff Highland on Mon Jun 23, 2008 3:12 pm, edited 1 time in total.

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Barry Daniels
PostPosted: Mon Jun 23, 2008 3:11 pm 
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Brazilian Rosewood
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Location: The Woodlands, Texas
First name: Barry
Last Name: Daniels
Quote:
Could you expand on this observation? It seems like a lot for wood bought from a fine wood yard, and not a construction lumber place. I cant imagine a piece of Jatoba shrinking 1" over 12 months.


Well, I don't know where you are buying your wood but whether it is a lumber yard, or a fancy wood boutique, they will not have wood at a stable state that matches your shop conditions. And to ensure full equilization, you have to age wood in your shop for one year if it is one inch thick, two years for 8/quarter wood, so on. I know this is not convenient when you are first getting started. And if you don't have control on humidity in your shop it is a moot point anyway. Just buy wood and start building. But some day, when you want to step up to the next level of quality control, you should be aware of what is involved. It does make a difference.
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Michael Dale Payne
PostPosted: Mon Jun 23, 2008 3:17 pm 
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Old Growth Brazilian
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MayanArch wrote:
MichaelP wrote:
When you laminate you do not run the grain exactly parallel for best strength and warp resistance. Even a 2 degree variance gives large increase strength. the combination of the two help counteract each other. Just like with plywood the lamination of two or more pieces is vastly stronger than an equal thickness and length of a solid of the same species.


I studied Architecture.....and understood that laminate wood beams and plywood is stronger because the wood is mostly fill. The strength of the glue is what makes for strength. The mass of glue to the mass of wood in a guitar is much different than in a piece of plywood or laminate wood beam. I.E.........concrete is stronger than concrete block....the block is just fill, which adds strenght and stability.....but nowhere near as much as the poured concrete members....

Wow! That 2 degree sounds like an interesting thing to investigate.

Isnt all lumber subject to that variation......since the wood fiber rarely grows perfectly perpendicular to the centerline of the original trunk???

How much variation is there between the different exotic hardwoods when it comes to expansion and contraction due to humidity?


It is not just the filler and glue that makes the difference. The alternating grain orientation is the big key in stability and strength because one layer the stabilized the previous layer.

I don’t have a chart giving variance in expansion or contraction rates but a good guess would be that there could be as much 2-5% of variance in some exotic hardwoods.
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Jeff Highland
PostPosted: Mon Jun 23, 2008 3:17 pm 
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The 1 year per 1 inch thickness rule is a guideline for air drying timber from green (freshly cut from a live tree)
Not really applicable for timber bought from the yard which has already been kiln or air dried.
Agreed that some aclimatization time is good.
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Barry Daniels
PostPosted: Mon Jun 23, 2008 3:29 pm 
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Jeff Highland wrote:
The 1 year per 1 inch thickness rule is a guideline for air drying timber from green (freshly cut from a live tree)
Not really applicable for timber bought from the yard which has already been kiln or air dried.
Agreed that some aclimatization time is good.


No, not how I have always heard it. This is in regards to wood stablization.
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MayanArch
PostPosted: Mon Jun 23, 2008 3:48 pm 
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MichaelP wrote:
It is not just the filler and glue that makes the difference. The alternating grain orientation is the big key in stability and strength because one layer the stabilized the previous layer.


OK, the answer is in the words.....but could you please expand on "alternating grain orientation" and the "2% grain direction change"?

Wouldnt the best allingment have the concentric rings pointing towards eachother.....in order to avoid splitting at the glue joint?
(|) as opposed to )|(

If humidity is going to affect the neck............and it will according to what all of you are saying......its just a matter of controlling it............then does a piece of lumber become more concave by exagerating the rings of grain?

In other words, isnt the direction of the rings a big consideration when designing for humidity variations?
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Jeff Highland
PostPosted: Mon Jun 23, 2008 3:50 pm 
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Koa
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What can be more important than letting the sawn (and air or kiln dried) timber sit in your workshop for long periods is to dimension to near finished size then let it sit for a while before final leveling.
Eg roughing out a one piece neck blank and allowing it to settle before leveling the fretboard surface.
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Jeff Highland
PostPosted: Mon Jun 23, 2008 3:56 pm 
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Koa
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Location: Caves Beach, Australia
Mayan

Looking in crossection
|||
/|\
\|/

would all be acceptable
wheras /|/ would be less stable
Jeff
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Michael Dale Payne
PostPosted: Mon Jun 23, 2008 4:07 pm 
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Old Growth Brazilian
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MayanArch wrote:
MichaelP wrote:
It is not just the filler and glue that makes the difference. The alternating grain orientation is the big key in stability and strength because one layer the stabilized the previous layer.


OK, the answer is in the words.....but could you please expand on "alternating grain orientation" and the "2% grain direction change"?

Wouldnt the best allingment have the concentric rings pointing towards eachother.....in order to avoid splitting at the glue joint?
(|) as opposed to )|(

If humidity is going to affect the neck............and it will according to what all of you are saying......its just a matter of controlling it............then does a piece of lumber become more concave by exagerating the rings of grain?

In other words, isnt the direction of the rings a big consideration when designing for humidity variations?



We are speaking of necks. Therefore we are speaking of 3-7 pieces of quarter sawn wood the orientation offset of each piece restricts the cross grain expansion of adjoining piece because the grain is not parallel. The more laminations you have (alternating the grain orientation) the more stable the lamination as a whole. One lamination wants to move one way but the adjoining lamination restricts it because it want to move in a different direction. It is all about letting the natural direction of expansion of each piece restricting the movement of it's adjoining piece.

If you wanted the most stable possible then 90 grain orientation would provide that but then you would have true end grain exposed in the long plane of the neck on one or more of your laminates which leads to excessive finish absorbtion.
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MayanArch
PostPosted: Mon Jun 23, 2008 4:18 pm 
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Walnut
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Posts: 21
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Jeff Highland wrote:
Mayan

Looking in crossection
|||
/|\
\|/

would all be acceptable
wheras /|/ would be less stable
Jeff


Wouldnt \|/ be the best, imagining the fingerboard sitting on top of......and at the opening of the grain to create a U enclosed by a top? In engineering you want the curve of a half moon to be facing the angle it will tend to bend towards.........so you would want the open top of the U to be where you glue the fingerboard, right?
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MayanArch
PostPosted: Mon Jun 23, 2008 4:26 pm 
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Jeff Highland wrote:
What can be more important than letting the sawn (and air or kiln dried) timber sit in your workshop for long periods is to dimension to near finished size then let it sit for a while before final leveling.
Eg roughing out a one piece neck blank and allowing it to settle before leveling the fretboard surface.


I was planning to let the body (neck) pieces sit for 6 weeks in humidity controlled room........glueing them up.......then cutting the body (really neck in an Electric Upright Bass) in the CNC lathe.

IMHO this would make for the best cut body/neck piece fitment since I could apply a lot of pressure to the "runner sandwich" when gluing perfectly rectuangular shapes..........then I would cut the fingerboard several weeks later, and true up the wood surfaces that join the fingerboard to the neck/body.

My fear is having to make major changes to what will then be a "U" shapped column.....since the curved side of the U cant be counted on for parallel.

Then letting the full assembly sit for another couple of weeks prior to finishing.
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Jeff Highland
PostPosted: Mon Jun 23, 2008 5:07 pm 
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Location: Caves Beach, Australia
Doing what you propose will be fine.
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