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allowable variation from 1/4 sawn
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Author:  mikev [ Fri Jan 06, 2006 7:37 am ]
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I have a piece of Sitka I was going to use for an archtop, but it is about 9degrees off from true 1/4 sawn. is that ok? I could resaw at a slight angle and still get 8.75 width (its almost 2.75 thick), should I? It still will be off by 4 or 5 degrees. If I have a variation should I orient the grain in this fashion \\\\\//// so it will be correct in some of the arch?
Mike
Author:  Don Williams [ Fri Jan 06, 2006 8:05 am ]
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There are several schools of thought on this, but from what I hear, (don't quote me) a few degrees won't kill you, and is still considered quartersawn. But too much and you enter riffsawn, and then flatsawn. perfectly quartersawn is usually best, but I've had some great tops that were a little off.
Author:  Shane Neifer [ Fri Jan 06, 2006 8:19 am ]
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Mike, 9 degrees is about 2.5% and should be just fine! And if you can glue as you have shown that is even better but you do want to have the 'bookmatched' face up if you can.

Shane
Author:  Alan Carruth [ Fri Jan 06, 2006 8:34 am ]
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Yes, do glue it the way you showed, if possible. Remember; when you carve tha arch you will be making a surface that's at an angle to the plane of the wood, and what counts is how quartered the grain is relative to that carved surface. What you propose to do in gluing gives the least variation in quarter overall.
Author:  Larry Davis [ Fri Jan 06, 2006 11:55 am ]
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I hope this isn't a thread hijack, but on subject. We strive to mill and select woods close to quatersawn as possible for the many reasons we know....added strength of radial plains in temerate forest wood species, reduced movement of radial planes. We are really almost obsessed with radial grain orientation for acoustic wood. When pretty wood figures like pommele, birdseye and quilt are desired for use in acoustic work the protocols seem to fade because these are tangent milled figures. Why and when is it structurally "OK" to compromise the radial "rule"?
Author:  Shane Neifer [ Fri Jan 06, 2006 12:16 pm ]
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Larry,
Your points are spot on but I think that one area where the rule is not broken is for tops which are subjected to the tension of the strings coupled with the desire to get the top as thin as possible to have it vibrate and come 'alive'. In other areas of the guitar you can make the plates a little thicker to compensate for the decrease in structural strength, but at the cost of more mass.

Shane
Author:  mikev [ Fri Jan 06, 2006 12:19 pm ]
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hey give me back my thread !!!! No seriously thank every one for their replies. it looks like those 3 billets I've had for a couple years have a purpose in life.
Larry, my understanding is that on tops we need the 1/4 sawn strength to weight ratio it produces. Lighter tops for the same strenght means better vibes. In backs there is far less stress and therefore we might as well go for pretty. But I could be way off.
Author:  Alan Carruth [ Sat Jan 07, 2006 9:59 am ]
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There's more of a difference between long-grain and cross-grain stiffness in softwoods than there is in hardwoods. Thus there is more of a stiffness advantage in milling softwoods for vertical grain.

Dead flat cut can be almost as stiff across the grain as perfectly quartered. You really lose stiffness when the wood is skew cut. Of course, for a guitar back to have dead flat cut grain all the way across it would have to come from a darn big tree..... You can get perfectly quartered stock from anything, but maybe not very wide.

Fiddle makers try to use flat cut backs so that the curve of the annual ring lines follows that of the arch. This makes the grain as close to 'flat' as possible all the way across. Carving the other way would give flat cut in the center and skew as you go out. a flat cut back is more prone to cracking, though, as cracks often follow the medullary rays.

To my mind, skew is the cut to avoid. Also, wood with ring lines that change angle on the end. As the wood cures the ring lines tend to straighten out, owing to the difference between radial and tangential shrinkage, and thus wood like that tends to warp. Flat to quarter is the extreme of this, although it's unavoidable sometimes.

Author:  Dennis Leahy [ Sun Jan 08, 2006 8:41 am ]
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[QUOTE=Shane Neifer] Mike, 9 degrees is about 2.5% and should be just fine!
Shane[/QUOTE]
I'm not saying that I know how far away from dead-on vertical grain is still acceptable for soundboards (I don't), but I'm curious about your math.

If a board is perfectly quartersawn (||||||), that's 0°, and if a board is perfectly flatsawn (======), that's 90° off the quarter. So, wouldn't 9° be 10% off, rather than 2.5% off? I think you might be thinking in terms of a full 360° geometric circle, rather than the possible grain direction variation in an individual board.

Again it may be perfectly acceptable to have a soundboard with grain 10% off the quarter; I'll leave that to those who have actually built guitars with off-quarter tops. My gut tell me that in this range (10%) the only issues would be possibly aesthetic issues, such as making a top with color streaks/stripes look well-bookmatched. But again, for the sonic properties, I'd defer to those who have actually built with off quarter tops (something many builders may never have done.)

Dennis
Author:  Shane Neifer [ Sun Jan 08, 2006 11:06 am ]
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You're right Dennis! I tease my wife about her math all of the time so don't tell her or I will not be able to have fun with her anymore!

Still, I think he will be fine, especially with curved plate like he is planning.

Thanks

Shane
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