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When I buy blanks for braces, they come in a set of 8 or so. I get them pre-thicknessed (to 8 mm).

I've been sorting them depending on number of growth rings, as a rough and ready indicator for "strength". I then look at how quarter sawn they are and how consistent the grain pattern is.

The latest lot ranged from 4 to 16 growth rings (in the same width of 8mm). Here they are:



I guess my question is whether this is a good rough & ready way to select which blanks to use. Or do other people use other ways?

I don’t worry about the growth rings. If my brace stock isn’t already split, I split it to find the runout. I do all of my cutting and shaping of the gluing surface parallel to the split so that the brace has no runout. After the braces are glued to the plates, I cut the height down and shape them to get the strength I want, testing by flexing and tapping as I go.

A brace with runout will not be a strong as one without and will be more likely to break, sometimes in places that are very inconvenient.

I take 1/4 sawn blanks of the same dimensions and drop them on the bench, grade them by the "ping" or vibrational frequency as they hit the bench.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

As bobgramann says, runout is the most important thing.

Grain count has nothing to do with stiffness. The Young's modulus along the grain (E-long), which largely determines the stiffness at a given dimension, depends mostly on the density of the wood, and also the ratio of earlywood to latewood. Hard late wood, the dark lines, adds stiffness, but it adds density faster, so the ratio of stiffness:weight of the final brace will be lower if the late wood lines are heavy. Low density wood needs to be left a bit bigger, but ends up weighing less at a given stiffness.

In use, bracing makes up only a small part, maybe 25%-30% of the total weight of the top, even though it accounts for most of the stiffness. Saving 5% of the brace weight by using low density bracing means you've shaved off 5% of 30% of the weight of the top: a little more than 1% of the total.

That assumes that you're actually measuring the stiffness of the top/braces, and working toward an acceptable minimum. If you're working to dimension you're brace stiffness and mass is going to be a variable as the wood you're working with. Samples of Sitka spruce that I've measured can be as much as 20% above or below 'average' density and E-long, and the same goes for any other species.

In the end, though, it doesn't matter how 'good' the brace material is if it splits because of run out.

I agree with Bob and Alan. Runout is important. If the brace splits, nothing else matters.

What is your source for getting the brace blanks cut and thickness sanded like that?

I bought a fair bit of bracewood from a mill. They split the billets for the tops and when the billet gets too small, they sell it for bracing. The other bracewood wood I have came from Shane at High Mountain. They came in wedges and are from the outside of the tree, so it's mostly sapwood.

Brent

With spruce braces, density is a much better predictor of stiffness than grain count.

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John

The brace blanks come from Rivolta, one of the main tonewood suppliers in italy. My assumption was that they would come from split billets but that is just an assumption on my part. I'll check!

Thanks everyone else for the input. So to summarize, Young's modulus roughly correlates with density, which also (at least in the relatively small sample that I've looked out) also correlates with growth ring count. However, given the cube rule for stiffness, less dense blanks provide the same level of stiffness at a lighter weight, even if they need to left slightly higher.

However, the discussion on stiffness is much less important that runout. I'll split the blanks and see how much runout there is.

The first one i've split seems to be very straight. I take it i'm splitting it in the right direction?

Well looky there, another rare bird that uses flat sawn bracewood product! We at Alaska Specialty Woods, Inc.- alaskawoods.com , produce that cut of bracewood for Lowden Guitars in large quantity and always have it on hand for others as well. But ours is cut at 1"[24-25m] thickness And of course we have the VG cut of sawn and split face as well.

Honza, I was friends with Andrea. I met him at Luthier shows back early 2000's he came to visit me in Alaska in 2008 and selected a pallet of about 800 High grade sitka guitar tops that we shipped to him in Italy. He told me he was 3rd generation in that business. We have 3rd generation here at ASW too. But they are just playing in the sawsudust right now. But in aniother 8+ yrs they will be into the production too.

I can't speak to their brace wood, but I inquired with them to find out if their soundboards are sawn from split billets and they told me verbatim "I'm sorry but our sets are not sawn from split logs.". That might be okay for violins, but if I'm ordering top wood sight unseen for guitars that's a dealbreaker. For braces, you can at least split them yourself, and their prices are reasonable.

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I like Rivolta. I live a couple of hours away so I can go and hand select stuff, no pressure to rush. Any they do lot's of thicknessing and planing for me as I don't have the machines at home. Nice people!

Thanks for the reply. Though I can't quite tell if it's serious or not! Flatsawn braces????

The one in my picture is waiting to get cut down. I split it to check for runout. I take it I'm splitting it in the right direction? Your post has got me a bit confused....

OK, thanks for letting me know. That's interesting. Next time I go I'll find out exactly what the story is, split or just quarter sawn.

Luckily for me I live close by, so I get to hand pick, rather than sight unseen. Though I'm not exactly sure how to recognize runout, any hints?

One easy way to tell is to take a picture on your phone with the flash enabled. If the reflection of the flash is even across the two boards, the runout is minimal. If the reflection skips at what would be the center seam, looking sort of like -_ then you've got runout at the center. If there's a long fluorescent or LED light above you that works too. Try it on some tops you already have and you should see what I mean right away.

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That's a great point, Josh. The light bar trick has been helpful for me. I actually demonstrated it during the monthly roundtable meeting back in July. Here is a direct link to the spot in the video where I show it - https://youtu.be/j70VsikbmaY?t=2293

Note for Tapatalk users: If it doesn't open at the right spot, fast forward to 38:00 minutes in.

Brad

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Nice demonstration, Brad. Flipping the board is a good trick for those instances when the runout isn't a dealbreaker too.

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That looks like a great technique, thanks @jfrench

Flipping end for end does not change the runout.

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John

OK well this was interesting.

I split all the blanks, ten or so in total. Most were pretty terrible, I was quite surprised. Of the whole lot only two gave a length long enough (once ripped along the split) for X braces.

Thanks everyone for your input, this has been really useful!

Here's 3 of the set of 10. The top two I'm going to use as x braces, the bottom one is representative of the others. Pretty terrible runout!