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What are your thoughts on quarter & flat sawn lumber? Which one cracks the easiest from drying out or humidity changes throughout it's life? I'm not asking which one is stronger.Just which one is more prone to cracking from humidity changes,which would be the same when seasoning.I'm not going to say yet as i want to see what others think on this subject.

flat sawn is not good for luthiery. You want the grain to be as vertical to the face. Flat sawn allows too much movement and is too unstable for most guitar building applications. Quaterted is the best and most stable wood for all wood working
john

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John Hall
blues creek guitars
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Risk of cracking is probably best looked at as a resulting effect of rate of dimensional change with change in moisture content. In that perspective, flatsawn woods would be at a higher risk of developing cracks in any system where the wood spans an area between relatively constant restrained boundaries (such as a guitar top spanning the rims). Dimensional change with humidity change goes in this order, from least to greatest; longitudinal, radial, then tangential.

It moves the least along the length of the grain (longitudinal). This dimension is our least concern, as in addition to it showing the least movement, it is the same in either quartered or flat. Movement across the grain is much greater however tangentially (flatsawn) than it is radially (quartered, or rift sawn). This means that a flatsawn soundboard or back will shrink and swell more than a quartered one within the same range of humidity. Because of this, it stands to reason that a flatsawn board will be more prone to splits, cracks, and seasonal shifts than a quartered one.

In seasoning, flatsawn can be more prone to cracking if the ends are not sealed, but if well controlled it can be just fine. And though I know you weren't asking about strength or stiffness, in many woods you'll find very little, if any difference between the two. Many instruments in decades and centuries past cut braces for example, almost indifferent to grain direction and I don't believe it had any impact on stiffness. They may split or crack differently when shocked (or over-enthusiastically scalloped), though I honestly don't know which way would be favorable to the other. I suppose that may rely on things like runout in the quartered braces, though I really don't know.

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Eschew obfuscation, espouse elucidation.

Here is a good link to some data regarding movement of wood. Tangential movement is greater than radial in all of the wood species listed and in many species the radial movement as a percentage can be half that of tangential.

Radial corresponds to quartersawn and tangential corresponds to flatsawn.

http://tnvalleywoodclub.org/Articles/Wood_Move.htm

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I sense a trick question here
In furniture neither is prone to cracking if not restrained and one uses proper techniques. In a guitar I don't know. So I don't think it would be the same as when seasoning because there are so many variables in service. Even if flatsawn wood is more resistant to cracking (I don't know for sure I am guessing that is where you are going here ) , the fact that on average most spieces will move almost twice as much in the tangential plane as the radial may change the equation. So maybe the extra movement may make it more prone to cracking in service even if when drying if may not be. I can see where when drying flat sawn will just cup but not split or crack. Hmm, now that I think about it I would say that the quartered might split a bit easier when seasoning.
Link

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Isn't it rather common to use flatsawn curly maple for backs?

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Curl in maple shows best on a quartersawn surface.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

You're thinking of quilted maple.

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Jeremy Douglas

Isn't it common to use flatsawn curly maple for backs?



Edit: Do flatsawn birdseye or quilted maple backs have problems?

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This back is being replaced after Christmas and a Quarter sawn back will be used...Larry

I'd say that birdseye maple does have more of a problem with cracking than well quartered curly maple. It's hard to say, since you tend to see a lot more curly than bird used in guitars. I can tell you that splinting cracks in bird is no picnic: they wander.

The cut that's _least_ prone to cracking is 45 degree skew cut, in my experience. It also has the lowest cross grain stiffness, of course, so you seldom see it in guitar tops, and only once in a while in backs. It's great for harp soundboards, though, and sounds fine.

There is a hidden problem in flatsawn wood as well; cupping. Given the difference between tangential and radial shrinkage there is a tendancy for a piece of wood to shrink in such a way that the anual ring lines on the end of the piece straighten out. This causes the board to cup across the grain if there is any curvature to the ring lines to begin with. On a well quartered piece the angle of the ring lines doesn't change much as you go across the board, and it won't cup much, if at all. You could avoid cupping on a flat cut piece if the tree it was cut from had infinite diameter, so that the ring lines didn't curve. There never were many trees that approached that size, although, of course, they had a LOT of nice clear wood in them. Any flat cut piece of wood is likely to be pretty flat for a few inches across the width, and then run to skew cut or even pretty close to vertical as you go across. This sets up a lot of cupping in areas of the piece, and concentrates the stress in those areas.

Also, with flat cut wood the medulary rays run through the piece, not across it. These little bundles of cells running along the radius are what give quartered wood it's high croswise stiffness and low shrinkage, I believe. However, they also weaken the bond between cells in the tangential direction, making the wood more likely to split along the radius, as anybody who uses a wood stove can attest.

Thus it takes less force to split a flat cut piece than a quartered one, and there is usually more force trying to do it, from the difference in shrinkage and the greater proneness to cup.