One piece back?

[Fathand]

I have in my stash a piece of roughly 1/8" Honduran Mahogany about 20x 24". I am hoping to build a J-45 sometime in the near future and noticed that some older ones had one piece backs.

Is there any advantage, other than nostalgia, to build with a one piece back? Any disadvantages?

I know I will save the work of the back seam joining process. Is warping or cracking any more likely long term?

[runamuck]

Originally Posted by Fathand

I have in my stash a piece of roughly 1/8" Honduran Mahogany about 20x 24". I am hoping to build a J-45 sometime in the near future and noticed that some older ones had one piece backs.

Is there any advantage, other than nostalgia, to build with a one piece back? Any disadvantages?

I know I will save the work of the back seam joining process. Is warping or cracking any more likely long term?

If the wood is quarter-sawn across its entire face there's no disadvantage structurally or greater tendency to crack. Other than that it is an aesthetic issue. Many prefer a back seam and inlay simply because that's what's familiar.

[John Arnold]

If it is slab cut, there is a greater chance of cracking. The most likely location is at the peak of the cathedral, since that is where the growth rings are parallel with the face. The weakest plane is radial (perpendiculer to the growth rings).
That said, Honduran mahogany is one of the most stable woods, with very low tangential shrinkage specs.
Many of those Gibson one-piece slab mahogany backs have survived just fine.

[Fathand]

Originally Posted by John Arnold

If it is slab cut, there is a greater chance of cracking. The most likely location is at the peak of the cathedral, since that is where the growth rings are parallel with the face. The weakest plane is radial (perpendiculer to the growth rings).
That said, Honduran mahogany is one of the most stable woods, with very low tangential shrinkage specs.
Many of those Gibson one-piece slab mahogany backs have survived just fine.

Thanks, I'll check grain orientation. I bought this piece of wood in the early 1980s when I knew nothing of grain, I don't recall much of what it looks like.

[Hexcore]

All I can add to John's expert comment is that you'll want to make sure that the piece has been seasoned and stored well so that you don't get any movement if it has to restabilize. Personally, my outlook is that simple is generally better, so not doing a center seam has appeal. Also, I just love evidence of the great, big trees that grew on this earth -- floorboards, guitar backs, furniture... nice to see examples of work where we don't have to glue up small pieces to make a big one. I hope your build comes out great.

[H165]

Many of those Gibson one-piece slab mahogany backs have survived just fine.

Yep; and thousands of old 1-piece Harmony H165s, H162s, and Sovereigns are also doing fine 70 years later.

[John Arnold]

My experience with the one-piece Harmony backs is that those were better quarter cuts than the typical Gibson.
One aspect that I haven't investigated is whether the Harmony mahogany backs were sliced like veneer. That was definitely the case with their birch.
Slicing veneer that thick will result in micro cracks on one side..... the side that was against the knife during the slicing. Using one-piece backs and non bookmatched sides allows for placing the cracks on the inside.

[RogerHaggstrom]

If you get a crack in the bottom with a one-piece, the crack will not be straight and sometimes hard to close when repairing. A two piece bottom often have the crack occur in the straight middle glue joint.

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