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How do you arch the back of an acoustic?

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I seem to be drawn to acoustics that have an arched back. I guess it seems they produce a richer tone to me in a smaller body size. I find dreads too big to be comfortable to play for a while, so I'm chasing a GC or OM body size, maybe smaller, and I'm thinking the arched back will increase the bass response and volume a bit. If I were to do this out of a 2 piece back, how do you get the arch? Do you bend/shape the pieces before you glue them together? Do you glue then shape? How do you shape it? Let's say, for discussion sake, I'd like to put an overall 5/8" arch to the back. Is that resonable?

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Honestly, I can't answer your question. It might take awhile (or not) for someone to read and post a good answer. You could try looking at some guitar building books (ie. Benedetto's book on arch tops, or Melvin Hiscocks book). I know most on this site are solid body builders, so wait for more answers.

Read this, it may or may not help.

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With classic arched backs (and tops), you start with a blank (typically 2-piece bookmatched) that is at least as thick as the height of your desired arch. Then start carving away (planes, scrapers, angle grinder, whatever gets the job done) on both sides of the blank until you have your arch. It is not bent, there is no stress in the wood whatsoever.

There are lots of ways to do it in detail. I highly recommend the Robert Benedetto book "Building an Archtop Guitar", the video series is also great as you can actually see how its done (a picture's worth a thousand words here). It's all about thickness (wood-species dependent), how the thickness changes from the top of the arch to the edge (the "recurve"), and "tuning" the back (e.g. continuing to shape the recurve) after it has actually been attached to the guitar. The price you pay for these will be well invested if you ever build even a single archtop.

I also know a friend-of-a-friend who's father worked for Gibson for ~4 years and who built many archtops; he basically confirms the Benedetto way of doing things.

I know that some pro builders use bent laminates to do basically the same thing, but carving it out of a single hunk of wood just seems better (and simpler) to me.

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Yeah, if you aren't carving the arch into the back, the traditional way is to trim a curve into the braces (on the edge you glue to the back) and clamp them flat to the back. When the glue dries and the clamps are released, the braces spring back and the back has a curve in it. That's the way it's done in Sloane and the Cumpiano/Natelson books.

Don't know if arching will have the results you desire.

You might look into a wedge back, as a increasing volume (cubic inches not dB) in an ergonomic little package.

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according to this, you just use brute clamping force/pressure to get the arch:


They sell standard jigs for dreadnaughts but I'm not building a dreadnaught. :D

That's exactly it. When I worked for a luthier bracing the tops and backs was my job. The back/top is placed in a hollow form, and the braces, which have the same radiused shape as the hollow form, are glued in place one at a time and clamped with go-bars. The frame, or side assembly of the guitar also has the arching sanded into it.

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