Brace stiffness, vertical vs horizontal grain

[Dave M]

I was sceptical of the statements by many people that grain orientation was important for stiffness of softwood braces. I did some tests and within my experimental error I could see no difference between grain arranged horizontally or vertically.

However James Blilie has reported some great work in GAL 128 where he has tested many samples for this, and other properties, and discovered that there is indeed a difference, with vertical grain giving around 20% more stiffness which is pretty significant.

He reports various other results such as that density of grain lines does not seem to affect the longitudinal stiffness. Well worth getting hold of the article.

It demonstrates that you really have to think through the sort of experiment that needs to be done to prove a particular point. Large sample size being one important factor. My work simply didn't look at enough pieces of wood

[TallDad71]

Having just read Somygi's book I am led to believe that your assumption is correct, grain direction is less of a factor than one might think.

I have done some of my own tests and it appears that the density of the wood has more effect than the grain direction on the deflection readings. By density I mean weight over volume and not grain line count.

I was also surprised to see that tapering of the sides of a brace bar has surprisingly little effect on the deflection readings. The only thing I did notice is that the cross section of the taper should resemble more of a trapezium than a triangle. Keeping a degree of flatness on the top of the bracing was crucial and as soon as the tapers met the deflections changed markedly. This is useful to know as it means that once you have optimised your soundboard you can play around with losing weight without losing stiffness which may help achieve the results you are after, i.e. increased monpole response.

[Trevor Gore]

Probably worth checking out this post and Al's response a couple of posts down.

[Steve.Toscano]

Didn't torres (or fleta, or hauser, or another of the big name makers) was found to be useing flatsawn spruce on all transverse braces...?
I think i read this in a semi recent GAL.

[kiwigeo]

Didn't torres (or fleta, or hauser, or another of the big name makers) was found to be useing flatsawn spruce on all transverse braces...?
I think i read this in a semi recent GAL.

Lute braces are often laid in with grain horizontal......but then again just about everything about a lute is "weird" (eg the mysterious J brace aft of the bridge).

With many of the great builders I suspect that they may have used flat sawn bracing simply because they couldn't get or afford quarter sawn stock.