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Thread: Pine For Bracing?

  1. #1

    Default Pine For Bracing?

    What's the difference between using spruce vs regular cheap pine for top and back bracing?

    I've heard of Bunya Pine being used but I can't source any at a cheap price.

  2. #2
    Registered User sunburst's Avatar
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    Default Re: Pine For Bracing?

    Stiffness to weight ratio. Spruce is stiff for it's weight, so that is the reason it is the standard for bracing (and for tops). If the ratio is good with another wood, it will be fine for braces.
    In fact, the shape of a brace; height, width, contour, can be manipulated to adjust the stiffness vs weight of the brace, so braces of the same weight and stiffness can be made from different woods, or braces of different weight and stiffness can be made from the same wood.

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    Café habitué Paul Hostetter's Avatar
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    Default Re: Pine For Bracing?

    Spruce also has a lot more strength in its grain. Most pine would shear across the grain in ways spruce never would. This is different than stiffness. To get the equivalent strength of spruce you'd need so much pine it would kill the sound of the top.

    There's no compelling reason not to use nice vertical grain spruce. It's already so cheap, why look for something else that's allegedly cheaper, or choose it just for the sake of doing something different. If you live in Oz, Bunya might be worth investigating.
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    Middle-Aged Old-Timer Tobin's Avatar
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    Default Re: Pine For Bracing?

    Quote Originally Posted by Paul Hostetter View Post
    Spruce also has a lot more strength in its grain. Most pine would shear across the grain in ways spruce never would. This is different than stiffness. To get the equivalent strength of spruce you'd need so much pine it would kill the sound of the top.
    I'm going to disagree on that point, with the qualification that it really depends on what species of spruce we're talking about, versus what species of pine. "Spruce" encompasses many different spruce trees, and so does "pine". So there is a lot of variation between species.

    For example, in bending, the design value that structural engineers use for select structural graded Alaskan spruce is 1400 psi. Sitka spruce is 1200 psi. Southern pine is 2850 psi. That's more than twice as strong in bending, for the same cross-section. An Eastern white pine would be 1275 psi. Which is still stronger than Sitka spruce but not as strong as Alaskan spruce.

    In shear, Alaskan spruce has a design value of 160 psi. Sitka spruce is 140 psi. Southern pine is 175 psi. Eastern white pine is 135 psi. Once again, Southern pine is strongest.

    Stiffness is defined by the Modulus of Elasticity. The design value engineers use for Alaskan spruce is 1,600,000 psi. Sitka spruce is 1,300,000 psi. Southern pine is 1,800,000 psi and Eastern white pine is 1,200,000. Southern pine is stiffest.

    So as you can see, Southern pine is vastly stronger and stiffer than spruce across the board. Eastern white pine tends to be stronger than some spruce, but weaker than others. The kind of pine we get down here where I live is usually Southern yellow pine, which is very heavy, but very hard and strong. The construction guys hate it because it's so heavy, it tears up their saw blades, and it's hard to drive a nail into. But they love white pine because it's soft and easy to cut or nail into, and it weighs very little. We typically don't use spruce because it's expensive to get down here for construction purposes.

    But anyway, I agree that spruce is usually the best choice for braces or other instrument parts. Not because it's strongest, but because it's very light. In engineering, we use the specific gravity (G) of woods for this. Alaskan spruce has a G value of 0.41, Sitka spruce is 0.43, Southern pine is 0.55, and Eastern white pine is 0.36. So it's easy to see that Southern pine, although being the strongest and stiffest of all the species I'm comparing, is also the heaviest. It's interesting that Eastern white pine is actually lighter than spruce, but it's also the least stiff and the weakest in shear and pretty lackluster in bending.

    At the end of the day, it does make sense to use spruce. But I wouldn't say because it's based solely on strength, or even strength-to-weight. Southern pine is 34% heavier than Alaskan spruce, but it's more than twice as strong. So theoretically, you could use half the wood cross-section with Southern pine, and save weight over what you'd get with spruce. But I believe there are other factors at play here. The sonic properties of the woods, as well as their dimensional stability. Spruce tends to be more stable than pine, and resists warping/twisting. When this is considered along with strength and weight, spruce tends to come out on top for construction of instruments as well as aircraft.

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    wood butcher Spruce's Avatar
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    Default Re: Pine For Bracing?

    Quote Originally Posted by Tobin View Post
    Which is still stronger than Sitka spruce but not as strong as Alaskan spruce.
    Just FYI, "Alaskan spruce" = "Sitka spruce"...
    Yeah, there's some Black spruce growing in AK, but I'm sure we're not dealing with that species...

    And don't even get me going on all those numbers, which are gross generalizations....
    Jeech, just flex the stuff. If you like it, use it...

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    Registered User fscotte's Avatar
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    Default Re: Pine For Bracing?

    Didn't someone build a balsa mandoln once. So....

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    Registered User Timbofood's Avatar
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    Default Re: Pine For Bracing?

    I remember someone using laminated bracing a while back.
    My fuzzy memory is thinking it was spruce, rosewood, spruce?
    Cross grain lamination (a la plywood) maybe?
    I can see the concept but, boy howdy what a ton of work! And how much is the return.....really?
    I've said it before, I'll say it again,
    "Just because you can, does not mean you should."
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    Middle-Aged Old-Timer Tobin's Avatar
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    Default Re: Pine For Bracing?

    Quote Originally Posted by Spruce View Post
    Just FYI, "Alaskan spruce" = "Sitka spruce"...
    Yeah, there's some Black spruce growing in AK, but I'm sure we're not dealing with that species...

    And don't even get me going on all those numbers, which are gross generalizations....
    Jeech, just flex the stuff. If you like it, use it...
    I don't know beans about species of spruce, but the numbers I used are from the American Wood Council and the Western Wood Products Association, and I'm assuming they know enough to list them as separate species.

    You're right, though, that these design values are based on averages. Every tree is different, and it's maddening trying to condense the data into generic numbers. But that's why they have so many different grades of wood for each species (such as select structural, No. 1, No.2, etc. The design values change depending on the number of knots, the continuity of grain, and other variables. This is, of course, for large construction-sized members. A tiny chunk of wood to use in a mandolin brace is nothing. A luthier just has to go by his eye and instinct. I only posted the numbers to show that, on average, spruce isn't necessarily the strongest wood.

  13. #9
    Mandolin & Mandola maker
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    Default Re: Pine For Bracing?

    You should read the article by Blilie and Carruth on Wood Stiffness in the latest edition of the GAL.
    Peter Coombe - mandolins, mandolas and guitars
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    Café habitué Paul Hostetter's Avatar
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    Default Re: Pine For Bracing?

    Quote Originally Posted by Timbofood View Post
    I remember someone using laminated bracing a while back.
    My fuzzy memory is thinking it was spruce, rosewood, spruce?
    Yep. The Larson Brothers braced many of their guitars that way. The spruce (most likely Picea rubens) was the normal vertical grain, while the grain orientation of the rosewood sandwiched in between wasn't so important. You can see the X and the main transverse brace above the soundhole done that way. The Larsons also did a radiused top, decades ahead of everyone else.



    So as you can see, Southern pine is vastly stronger and stiffer than spruce across the board.
    Sorry, without species names or any documentation, I see nothing of the sort. It's important, when making sweeping declarations, to know beans about species of spruce. And to also know the history and ways of instrument making over the last 500 years or so. I reckon if it (whatever it is) was really that good, it would be in heavy use for instruments. It's not.
    .
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  16. #11
    Registered User Jim Adwell's Avatar
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    Default Re: Pine For Bracing?

    Southern yellow pine is stiffer and stronger than Sitka spruce per unit of volume, ie length width, depth. Sitka spruce is stiffer and stronger than southern yellow pine per unit of mass. We like to use spruce rather than yellow pine, because we are concerned with mass when making a vibrating sound plate rather than volume - less mass = louder sound, everything else being equal.

    I made a requinto guitar a while back using southern yellow pine for the top. As expected, it's quieter than a spruce or cedar instrument. The quality of the sound, outside of volume, is similar.

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