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I posted this question in another forum and have received some great responses. I thought I would try for some more in this forum:
How close to vertical do you require for braces? I've been trying to get very close to 90 degrees, but that can really reduce the yield from the brace stock I get which varies from 45 to close to 90 degrees. I know the definition of quarter sawn allows for variation from 90 degrees, but what is the consensus for spruce braces? I believe Alan Carruth has done studies that shows stiffness in spruce is largely independent of grain orientation
thanks Mike

The braces are small, so it is easy to get 90. Cut them one at a time!

Long grain stiffness does not vary much with the grain orientation, and the best split resistance is when the grain is about 45 degrees.
However, I like vertical-grain bracing, mainly because it makes them easier to carve. I just angle the saw when cutting braces, to make the grain as vertical as possible.
I would buy the brace stock from another source.

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John

I have seen some advocate flat orientation, i.e. zero degrees.

Thought I had posted this a few minutes ago. I guess I killed the page before it uploaded. Anyway, for what it's worth, it's always vertical for me. I have re-split or resawn sticks that were slightly off vertical, just to get them the way I want them. I'm no engineer. There might not be a valid reason for the way I do it, but that's the way I do it. And I have no plans to change any time soon.

....of course, upcoming posts on this thread MIGHT persuade me otherwise....

Mike give our brace wood a try. Usually close to 80-90 degrees

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I prefer vertical myself; I like to see the parallel lines of the grain run the length of the brace.

I have used Bob's stock , Good stuff.
If 75% of the brace grain runs out . I don't use it for structural braces.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks for all the great comments. I ordered stock from BobC this morning for future work, and I'll just cut the braces individually from my current supply to insure vertical orientation,
Mike

Bob, I ordered and received six engelmann brace boards. As advertised, they were from 80 to 90 degrees, with 4 of them being right at 90 degrees. Thanks for a great product!
Mike

I prefer perfectly quartered for ease of carving but I have measured the modulus some brace stock and I was surprised to find that the flat sawn side of a brace is slightly stiffer than the quartered side.

Partial hijack but I think it's relevant.

What do all of you think about runout out the side? Meaning if you are looking at the thin edge of the brace, the grain lines run straight & parallel to the sides but then curve and go out the side at some point, let's say 25% from the end. Use or discard?

Kevin Looker

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I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

I would use them.....unless they are warped. Braces get very little stress in the sideways direction. The failure mode is almost always in a plane parallel with the top, due to the runout from the tapered ends, or due to the notch at the X-crossing.
This radial plane is a weakness. Most woods (including spruce) split best radially (perpendicular to the rings).
That is why I say that 45 degree orientation is stronger.

Flat grain is in fact stiffer, but then you have a weakness parallel to the rings. To prove it is stiffer, I cut a perfect square of red spruce, then tapped it on adjacent faces. That vibrates it in the plane parallel with each face. In the flat-grained plane, the frequency was almost a semitone higher than the vertical-grained plane.

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John

Kevin,
With regard to your runout question, I honestly can't answer you with any scientific certainty. I've got a hunch that runout is more of an issue on the long x-brace members than in the tone bars, etc. That said, I avoid runout whenever I detect it. That's just the way I do it. I'm sure you'll get lots of varying opinions. I will be checking back in along with you, to see what more experienced builders have to say.
Patrick

Good brace talk guys. I always use right-on quarter sawn but just because I thought that was the norm. Keep the talk coming, I'm learning things by the minute....

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Joe Beaver
Maker of Sawdust

I only reject runout and bearclaw. Runout because it is less stiff and just as heavy, lowering the stiffness to weight ratio. I reject bearclaw because it's a pain to carve.

So, as long as it's not warped, would most of you use stuff like this?
Kevin Looker

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I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

I will cut so the grain is truly vertical, if it takes an extra billet or two so be it. The bigger thing to watch for is the cellular runout. This is is where braces will crack if stressed or impacted, it is also the what your chisel will grab when carving the braces and cause them to split. This is much harder to see but very important. here are some pics of a piece of maple I used in a demonstration to a student a while back to illustrate this point. The piece was simply split with a chisel and a sharp blow. As you see in the first pic I made the split at a point in the grain that was close to quartered. But look at how the split went anything but straight down the board. It follows the cellular structure of the wood, not necessarily the grain.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

I suppose you could use that terminology, but the split does follow the grain. Growth rings are not the same as 'grain'. Growth rings do not indicate runout, particularly with quartered wood.
I best way to avoid runout is to use wood that is cut from split billets.

IMHO, runout becomes objectionable from a strength standpoint long before it affects stiffness.

Probably not....because I think there is runout in those braces.

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John

Meaning runout that we can't see?

Runout through the thin edge?

Kevin Looker

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

Thread has be wondering.... Lots of pix in the past of belly rotaing, but not too many of what's actually going on with the braces.
Are the majority of braces failures:
a: Bending (allow the bridge ot rotate?)
b: Break
c: separate (Glue failure or other reason)
d: Your experience here...

and would grain orientation/runout been a root cause of the issue?

Never. I only use Western Red Cedar for braces and I split them off my own billets before sawing and sanding to dimension. Why use anything other than perfect?

I see fuzzed-up grain on the top surface where the grain curves. That means the grain not only curves side-to-side, but up-and-down as well. In this context, 'runout' means grain not parallel to the top surface, which is the surface perpendicular to the growth rings on a vertical-grained brace.


Bending that causes excess belly usually means that the brace is not tall enough. Since stiffness is proportional to the cube of the height, a very small change can eclipse any difference in the inherent stiffness of the wood.
Out-and-out failures are generally from the last two. Excess belly on older Martins is primarily because the X-brace comes unglued in the bridge area. Broken braces almost always happen because of an impact. That is why bracing design is driven by stiffness specification, rather than strength.


Sometimes, but it is rare in a factory guitar.

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John

While technically I suppose you are right as a split always follows the grain of the wood. When most speak of the grain of a piece of wood they are referring to the pattern formed by the early and late wood, ie. the visible grain from the growth rings of the tree, this is also the reference for quartersawn versus flatsawn. Not the very difficult to see medullary structures formed within the cellular structure of the fibers. There is grain runout and cellular runout, two related but completely different aspects of wood.

I use maple to demonstrate the structure of wood because it has some of the easiest to see cellular structure and the medullary cells stand out quite well. In the first pic again note the split crosses the visible grain. In the second we can see all the medullary cells clearly as they are full of resin and stand out. If we look closely at the split face we can also see the visible grain from the rings. Notice how the medullary cells cross the visible grain. It is the intersection between the visible grain lines and these cellular structures that determines the cellular runout. When they are at a perfect 90 degree interstection there is no cellular runout and the wood will cleave pretty much in line with the visible grains. When this angle skews in any direction the wood will cleave along these structures and cross the visible grain as in the top picture.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

I don't see the point in using layman's terms for something that every experienced woodworker should understand. I would just point out that 'grain' and 'grain direction' have different meanings... even to a layman.
Once again, growth rings are not determinant of grain direction, because grain direction is linear, while growth rings are a cylindrical structure.
'Seeing' runout:
The rays can be difficult to see on a tangential surface, but with magnification, they are usually visible as short lines. The grain direction is always parallel with the rays, as you correctly pointed out. If you extend these short lines, you have determined the grain direction without splitting the wood, and wiithout quartersawing it and checking to see if the rays are straight across the face.

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John