Back Thickness

[Jack Lord]

I overdid the thickness sanding on a mahogany back for a OO size guitar I'm building, it's about .080". Will this work or should I start over? Also, I haven't found a bracing pattern for the OO size yet, is it the typical Martin X? Anywhere I can get plans? Thanks.

[Dave Yelverton]

Jack

Here's a generic OO plan in pdf format. It's full size, so you can take it down to a printshop to get it copied. The plan's in the public domain so there's no problems about copyright. Grellier has a few other plans, so it's worth looking on his website.

Dave

[Jack Lord]

Thanks so much Dave, it's just what I need. I'm glad to find out about Grellier. What do you think about .080" thickness for the back in mahogany? Too fragile? - Jack

[Dave Yelverton]

Jack, I think the plan specifies 0.1". I don't pretend to be an expert, but IMHO 0.08" would be about the thickness to use for rosewood. You might get away with 0.08", but I generally find that mahogany is a bit too fissile for that. If you're feeling a bit insecure about this, how about laminating some mahogany veneer on the inside of your back? I also know a guy who layers his backs with spruce and he builds some amazing instruments. You could always start with a new back set but given the increasing rarity of mahogany that would seem an unacceptable waste!

Dave

[Evan Bradley]

I agree, or you could run two little narrow and tall braces down the middle of each side end to end to provide a bit more structural integrity, though not sure if this would dampen, guess it depends on the bracing....Good luck!

[Ned Knepp]

How about saving the too thin mahogany plate for a ukulele. I don't think it's too thin for that. You might even be able to get both the back and top from it.

Ned

[David Payne]

Jack,

I have noticed that every piece of wood is different (Captain obvious here) but did the plate seem too flexible before braces? I have come to rely on the "feel" of the wood to arrive at a thickness. Part of the problem with production guitars is they don't adjust dimensions depending on wood density and stiffness. If it seems too thin because it is too flimsy then you might be Ok with stiffer bracing, maybe not. How does the back plate respond to flexing?

Dave

[Tim Mace]

imo the thickness sounds ok for for the back if it's already been thicknessed to.080.Go for it.If it fails you'll know better next time!Mahogany can take it.And backs aren't under the stress like tops.

[Dave Yelverton]

I'd agree with David and Tim to this extent; mahogany is variable. For good mahogany I would say that at 2mm (.08") you've reached the safety limit. Any thinner and it will be prone to split easily and the back will be unlikely to form an even curve over the braces. For the quality of mahogany I've had in latter years, 2.5mm (0.1") is a safer thickness.

[Rob Mercure]

Several mahogany ("true" - "new world" - Swietenia genus) tops that I've measured including a Guild D-25 have had a 0.080" top thickness so if you wind up not using any of the other suggestions for this wood as a back piece you might consider it for a table. My first good guitar was a Guild D-25 and I think that true mahogany makes a great top wood with a great "non-boomy" response (but if you've seeking the "traditional/bluegrass" bottom boom, missing mid, emphasized treble D-28 sound mahogany won't do it).

There's always options in life if we're willing to open or stretch the "box" a bit .

Rob

[Tim Mace]

Mahogany lovers unite!I hope there will always be enough left to make an instrument.

[David Houchens]

. To do veveers you really need an odd number of layers IMO. All this extra work and end up with a back you didn't start out wanting.
I would save it for a 1-18 or another smaller guitar to build in the future, or a top.

[Jack Lord]

Thanks for all your help. After reading your comments, I feel that the .080" mahogany back will probably do fine. I haven't braced it yet, and it flexes just fine, no sign of fissility (I learned a new word). I'll brace it and see how it looks.