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I'm trying to design the back bracing for this guitar and thought I'd see what you folks would do. A little background, this is a guitar that I designed from a dream that I had. It has deep relief carving all over the back and sides of the guitar. To do this, I had to start with a back of .275" thick and had to do a triple lamination of the sides to get to that thickness. As you can imagine, it is a little on the heavy side. The back, now that it is carved is just barely heavier than the ziricote that I used on my last guitar, but this is where my question comes in. I am wanting to cut as much weight as possible on the bracing of the back to make up for it's extra weight. I've already decided on three braces instead of the four that I typically do. THe body size is 14.25 wide at the lower bout and 11.25 at the upper bout. So, would you do three parallel braces, or one across the upper bout to protect the central carving and an x for the lower? Other ideas are also welcome.
And by the way, it is all hand carved, no cnc's here. I have about an hour into each section except for the center piece which took about three hours to carve.

Wow! Nice concept and great carving job there.

With the extra thickness you probably don't need much bracing. How about a lightweight lattice bracing? My most recent guitars have a spruce lattice back bracing made from 1/4" high by 0.1" wide braces spaced at 3" centers. It is very light weight, yet has considerable strength.

Beautiful carving! I'm not sure about the bracing- almost loks like the areas not relief carved could be the braces- this idea makes my head spin-

all I can say is WOW. I bet that took some time to do!

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"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

Thanks, it has taken a long time, and will take a LOT longer to do the sides. Barry, thanks for the idea. I decided to do a little math just to figure out weight differences based on volume. If I were to use the lattice, it would use 3.01 in cubed, the parallel would be 3.03 in cubed, and the x would be 3.6 in cubed. So, there is very little difference between the parallel and the lattice as far a weight. How do you do the intersections in the lattice? Is it just a half lap like the traditional x brace? I was flexing the back a bit as well, and it is very stiff along the grain, but not that stiff across the grain. It sure would be easier to do the parallel bracing, but I do like the idea of the lattice bracing purely for the support it would offer the carvings. hmmm.

The joints on my lattice are just like an x-brace. Half lap with a thin reinforcement patch on top. This is not hard to do if you make a setup on a table saw to space the joints precisely at the chosen interval (3" for me). I chose a sawblade thickenss that was equal to the brace thickenss. So one pass of the sawblade made my joint. The hard part was making a jig to hold the bracing after the lattice was glued up, to sand a radius on the contact side to match the intended back radius of 15'. I will try to remember to post a photo this weekend.

Wow, amazing!
I wonder if the carving itself provides any stiffness?
That may affect your brace decision as well.

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Old growth, shmold growth!

First let me say WOW!!!! awesome work. I would think standard parallel bracing would work as well as anything else. How about an X-brace on the back?

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

What kind of wood is it?

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John

Thanks guys. The back and sides are Mahogany from Menards, so I'm not quite sure the exact species of it. I think I've settled on just doing the parallel bracing, but making it a little lighter than my normal bracing since there is extra thickness. I decided agains the lattice and x because I didn't want to add any more stiffness along the grain since it is already extremely stiff in that direction. Thanks for posting.
Here's a couple more pics of what's going on with this build. The top is Sinker Redwood and the rosette is Holly.

Simply incredible! what type of finish are you planing?

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

I agree, that is an incredible piece of art. It's almost a shame you are covering the neck block.

Are there other details inside you plan to carve? What about the heel and headstock?

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Jim Hansen

Amazing work!

Regarding bracing it, don't worry about any acoustical implications, the back will already be too heavy to be anything other than a non-live back. What I'd be worrying about is making sure that it is as immune to cracking as it possibly can be. I'd be going with enough bracing to make sure it holds its arch (3 ladder braces, gabled, 20mm high, 10mm wide, will be enough if the body length is less than 490mm) with some low "ribbon" braces between them. The ribbons (essentially just veneer) only need be about 1mm thick but ~20mm wide. If you're going to relief carve the ribbons, make them thicker!

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

holy crap

Thanks guys. It has been a labor of love. I've been pushing it really hard on this one trying to get it all carved so I can put the box together and thump on it a bit. Trevor, the back is fairly heavy, but not outrageously heavy. When I tap on it, it rings for about 5 seconds. But you may be right. In your experience, what implications would you expect for overall sound production?
Jim, I carved the heel block because it would be visible from the soundhole. The tail block won't be carved. The neck most likely won't have any carving out of the norm. The original plan that I drew had the neck with carvings, but it seemed to detract from the visual appeal of the back and sides. The headstock will have a similar feel to the rosette. It will be ebony with an inlaid carving out of holly. I really wanted to do brazilian hp, fretboard, and bridge, but I just don't have the resources to do it, so it will most likely be ebony that I have on hand. As far as fretboard inlays, I just can't make my mind up. If it were brazilian, it would be as minimalist as possible to not take away from the beauty of the brw. But if it is ebony, it may have a small abalone N at the 12th and some 2mm abalone dots.
Anyway, thanks again guys for the supportive comments. I really do appreciate them.

This is sick. It's this kind of work that makes me want to give up and persevere at the same time.

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Adam

There's a good discussion on backs over on one over the other forums: http://www.delcamp.us/viewtopic.php?f=11&t=63246. In a nutshell, a non-live back is a lot easier to get right. You sacrifice a bit of tone colour (as you don't get the back resonances appearing in the response function of the top) but you tend not to loose any volume, which you do if you're taking energy from the top to drive the back. There's more to it than that, but there's plenty more detail over on the "dark side"!

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Thanks Trevor for the link. That is some good info.

AHHHH I finally have the carving done on the sides. It still will require a ton of sanding, but at least I can finish bracing and assemble the box. I can actually do some building again. I've been sitting at the table carving non stop it seems for the past few weeks. Anyway, here are a few pics of the sides carved and the back sitting on them. At the heel area I added the corners since I took the photos. I had totally forgotten about them until I looked at the pics myself.

Andrew, just a quick reminder (you probably know this already, but it could be catastrophic if you didn't) make sure you have the back at moisture equilibrium at 40-45% RH before you glue any braces on. For your back, if your workshop is not at 45% RH, I'd be giving it two weeks or so (because it is quite thick in places) at 45% RH to get to equilibrium (8% equilibrium moisture content all through the wood).

If the guitar will live in a really dry place (typ. <20% RH) please get back if you don't know how to deal with that.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Thanks Trevor for the concern. My shop is kept at 45% rh year round, and the wood for this project has been stored there for a year. It's also been almost 2 weeks since I finished the back carving and it seems to have come into equilibreum now. It did move quite a bit right away, but has come back to flat for the past few days. I'm in MN so we have quite extreme rh levels throughout the year, so I've had to be pretty conscious about keeping things as close to constant as possible.

Sounds like all is good!

Would love to see some more pics when you're finished. All the best!

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Thanks for the help guys. I ended up following Trevor's advice and doing three parallel and then some ribbon braces between them. It's kind of funny that this bracing was stressing me out so much. I usually don't even really think much about my bracing for the backs. Anyway, here are a few pics with the box together now, and yes I forgot to take pics of the back bracing.

This is astonishing. It looks like you have sealed the top before it was glued to the sides. Is this so, or just an optical illusion? Great Work; thanks for the pictures. I can't wait to see how it turns out!

wow ...

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If trees could scream, would we be so cavalier about cutting them down? We might, if they screamed all the time, for no good reason. - Jack Handey