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Why quarter sawn tops..?
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=24651		 Page 1 of 1
Author:  Sondre [ Wed Nov 18, 2009 2:48 pm ]
Post subject:  Why quarter sawn tops..?
This is probably the stupidest question you have seen in a while, but how does it matter if a top is say 45 degrees off quarter?
Author:  Michael Dale Payne [ Wed Nov 18, 2009 3:21 pm ]
Post subject:  Re: Why quarter sawn tops..?
QS offers the best weight to strength ratios both cross and long grain
Author:  Hank Mauel [ Wed Nov 18, 2009 3:34 pm ]
Post subject:  Re: Why quarter sawn tops..?
As Michael said, better S/W ratios.
Think of a (steel) ruler, for example. Laid flat, like you were reading it, it's quite flexible and would need to be X times thicker to gain any semblance of rigidity...along with the associated weight gain. Now take that same ruler and stand it on edge and bear down. Incredibly stiffer for the same amount (mass and weight) of material.

Same goes for wood. Consider the annular rings (the dark grain lines) as the ruler. On edge (QS), they are very strong for their size, laid out towards horizontal, they flex more and more as the angle away from vertical increases. Then there is the issue of movement in the wood. The quarter sawn, well aged wood is going to remain in it's shape more readily that flat sawn (off QS), which will want to turn into a propeller blade under some atmospheric conditions.

So, think strength and stability for QS woods.
Author:  Sondre [ Wed Nov 18, 2009 4:34 pm ]
Post subject:  Re: Why quarter sawn tops..?
Thanks, Michael and Hank! I guess that's what I suspected

Suppose I have a top that is perfectly quartered behind the bridge, but it wanes off to 30 degrees at the widest parts of the lower bout. Do you think it will have an audible effect on the sound of the guitar if the top is a little sloppier in those areas?
Author:  Mattia Valente [ Wed Nov 18, 2009 5:09 pm ]
Post subject:  Re: Why quarter sawn tops..?
Well, stability yes. Strength not necessarily; isn't maple stiffer when flatsawn, for example?
Author:  Michael Dale Payne [ Wed Nov 18, 2009 5:26 pm ]
Post subject:  Re: Why quarter sawn tops..?
Sondre wrote:
Thanks, Michael and Hank! I guess that's what I suspected

Suppose I have a top that is perfectly quartered behind the bridge, but it wanes off to 30 degrees at the widest parts of the lower bout. Do you think it will have an audible effect on the sound of the guitar if the top is a little sloppier in those areas?


if it wanes off 30 degress it was cut from a very small diameter tree :D But to get at the crux of the question; the thicker the wood the more variation you will see because the tree grows in prety much a round shape. Therefore a 1" thick piece of QS will show more of the off quarter towards the outside of the plank than the center. but a 3/16" thick slab is such a small cross section there will be very little of the circular shape of the anular rings noticable.
Author:  JohnAbercrombie [ Wed Nov 18, 2009 6:45 pm ]
Post subject:  Re: Why quarter sawn tops..?
Mattia Valente wrote:
Well, stability yes. Strength not necessarily; isn't maple stiffer when flatsawn, for example?


I agree. Not just maple, either. To satisfy my curiosity, I just now tested a square of spruce and found surprisingly little difference between the flat-sawn and quarter-sawn stiffness (<10% difference in deflection with the same force applied ), though the quarter-sawn (grain lines parallel to the applied force) was a bit stiffer. Of course, some folks may consider 10% a 'huge' difference...

So personally, I wouldn't get overly concerned about grain angle changing a bit toward the edge of a top- though I wouldn't expect to see that in a good-quality top sawn from a larger billet.

I think the real reason has much to do with appearance- the appearance of a flat-sawn spruce top would be 'distracting', to put it mildly.

Cheers
John
Author:  Hank Mauel [ Wed Nov 18, 2009 7:09 pm ]
Post subject:  Re: Why quarter sawn tops..?
It would tend to make the top a bit "floppier" toward the edge, but since the top wants to "pump" air like a speaker cone, that extra flex may be a positive. Often a real stiff top gets thinned down around the edges after being glued to the rims. The whole box it then tapped for tone and if "tight" the lower bout up to the waist is judiciously sanded thinner the get additional flex. By default, this makes the center area around the bridge "stiffer" in relation to the edges and the string vibrations (energy) radiate outward towards the "more flexible" area. It's a balancing act, but one that you will need to know about as you go down the road of building guitars.

FWIW, LMI considers 20 degrees off perfect quarter as acceptable, anfd they process a lot of wood.
Author:  truckjohn [ Wed Nov 18, 2009 9:24 pm ]
Post subject:  Re: Why quarter sawn tops..?
Typically Spruce is strongest when either perfectly flat sawn or perfectly quartersawn.... and is most flexible when 45* off quarter.....

1 good reason we don't have flat sawn tops is.....
We don't have many trees big enough! Good luck finding a top out of a tree that was large enough to have 1 growth ring not runout across an entire 8 1/2" wide top half.... at 0.10" thick...

Then there is that matter about flat sawn wood cupping and bowing with humidity in both length and width directions.. while Quartersawn wood mostly only changes in length..

Quartersawing tend to be a pretty good compromise....
That said, zillions of guitars (And pieces of furniture..) have been made with Flat sawn stock...

Thanks

John
Author:  Alan Carruth [ Thu Nov 19, 2009 4:16 pm ]
Post subject:  Re: Why quarter sawn tops..?
What John said.

Typically, spruce that's cut dead on the quarter will be something like ten times as stiff along the grain as across. Dead flat cut it would be more like 12:1. I just measured a 45 degree skew cut piece of Sitka yesterday, and the stiffness ratio was about 62:1. I've seen skew cut wod that was even floppier, and have heard of it measuring out at 100:1. In all cases the stiffness along the grain is uneffected: you just lose cross grain stiffness if you use any cut except perfectly quartered.

Dead up quartered wood will have the lowest cross grain shrinkage, but that doesn't always mean it will have the most resistance to splitting. In fact, skew cut wood is much better in that respect: the added flexibility seems to allow it to 'give' enough to more than make up for the increase in shrinkage. When I make a small harp I usually use dead skew wood for the soundboard, becuase those things do tend to crack a lot. Some of the other harp makers tnink that it will make the instrument sound 'dead', but it doesn't: cross grain stiffness is not an issue on a harp.

Dead flat cut wood is almost as stiff across the grain as perfectly quartered, but, of course, you won't find a piece of wood that's perfectly flat cut all the way across. The stiffness is going to vary a lot from one place to another. Flat cut is also nmuch more prone to splitting that well quartered wood, which is held togehter by the medullary rays that also give it the extra stiffness across the grain. violin scrolls are cut so that the woo din the neck is flat cut; the opposite of what you're told to do ith a guitar neck. But on the violin the important thing is to hold the scroll toghether against the wedging action of the pegs, and that means having the quartered face on the side of the scroll.
Author:  Sondre [ Thu Nov 19, 2009 6:37 pm ]
Post subject:  Re: Why quarter sawn tops..?
Thanks for posting, folks! I appreciate it

Alan, if you had just the shortest comment on my bracing thread, I would be overjoyed!

Thanks again, everybody
Author:  the Padma [ Thu Nov 19, 2009 7:01 pm ]
Post subject:  Re: Why quarter sawn tops..?
Sondre wrote:
Thanks, Michael and Hank! I guess that's what I suspected

Suppose I have a top that is perfectly quartered behind the bridge, but it wanes off to 30 degrees at the widest parts of the lower bout. Do you think it will have an audible effect on the sound of the guitar if the top is a little sloppier in those areas?



No. Why should it?

the
Padma
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