One piece acoustic back?

[Pepe Silvia]

I happened upon some very old Brazilian rosewood. I have four pieces that are large enough to resaw into two backs or two one piece backs. My question, is a one piece back more desirable than a bookmatched back? I know that a one piece back is rarely if ever seen. Is that because of the available lumber not being able to accommodate the dimensions, or is there other reasoning behind not using one piece backs?

Here is a picture of two of the pieces.

[Alan Carruth]

I've seen a few instruments with one piece tops, but can't think of one with a one piece back. Those tops were from really big trees, and were well quartered all the way across. Aside from the cross stiffness, that's the most stable cut.

It's always hard to tell with BRW, of course, but those don't look as though they're well quartered all the way across. This would introduce some cross grain cupping someplace in the back. Making it from narrower pieces minimizes the amount any one piece cups. Book matching them, which reverses the grain direction and thus the direction of the cup helps even the stress out some.

Those look as though they came from a chest or piece of furniture. Do you know anything about the history of it? If it's been around for a long time, and particularly if it has spent much of that time in a dry or variable climate, the wood may be stable enough to try a one piece back. It's hard to say. BRW is not the most stable of woods, and even old, well quartered stuff can decide to warp or check sometimes.

[Pepe Silvia]

Hey Alan, thanks for the reply. What you said makes a lot of sense. As far as the lumber, it did come from an antique desk from the 1800's. Actually the desk looked as if it had been made out of salvaged lumber itself. So it's hard to put a good date on it. I don't really know the history of it. I've made a few fingerboard blanks out of it that are very stable, even though they are flat sawn. So I imagine these mostly quartered pieces will also be very stable.

[printer2]

And you need a bandsaw that can cut the full width of the board.

[Pepe Silvia]

I'm thinking that two sets of two piece backs is the logical way to go.

[Frank Ford]

1. Are you certain they are solid wood pieces? I ask because high-end furniture was usually made with solid core and veneer faces. It's about the stability, you know. Over the years, dozens of folks hava approached me with antique square grand pianos they swear were solid Brazilian. Invariably they were veneer construction. Anything else would be too unstable.

2. I have had some experience with one-piece backs. Gibson and others did that without any notice, and it appears that nobody much cares. I had my old pal Brian Burns resaw some huge super figured maple pieces into one-piece guitar backs.

Both Santa Cruz and Taylor made some instruments for us to sell, and in both circumstances I spent some time talking up the rarity of the one piece situation. My conclusion after numerous conversations is that the "greater" guitar buying public doesn't care.

3. Mandoins, violins, cellos and other historically significant instruments have one piece back, and still "they" don't care much about it.

[Pepe Silvia]

Hey Frank

1) 100% positive it's solid pieces. Believe me, I was as surprised as you. I was certain that much of the desk would be veneer. None of it was!

2) That's good to know. It would seem like a one piece back would draw a premium, but I guess not.

[Mr. Paul]

My 46 J45 has a one piece back. I didn't consider it important when buying it and wouldn't talk it up as a desirable feature should I ever put it up for sale.

[John Arnold]

One piece mahogany backs are not uncommon, particularly on older Gibsons and Harmonys. Mahogany trees can get huge. But a one piece rosewood back is very unusual. Other than the novelty, I see no advantage. Of course, a one-piece back that is not quartered loses symmetry when compared to a two-piece bookmatch....unless the heart is well centered.
I would not worry too much about stability, since your wood is so old.