Acoustic tops are thin, but what if...

[Mike McLenison]

What if tops were cut out of half inch spruce (for example) and CNC milled so the bracing was wasn't glued but part of the original top? They would never come loose and would be a perfect part of the top. More expensive probably but better structurally and tone-wise?

[RP]

Originally Posted by Mike McLenison

What if tops were cut out of half inch spruce (for example) and CNC milled so the bracing was wasn't glued but part of the original top? They would never come loose and would be a perfect part of the top. More expensive probably but better structurally and tone-wise?

Better tonewise? Highly unlikely....

[Lost Sheep]

Originally Posted by Mike McLenison

What if tops were cut out of half inch spruce (for example) and CNC milled so the bracing was wasn't glued but part of the original top? They would never come loose and would be a perfect part of the top. More expensive probably but better structurally and tone-wise?

I suspect the direction of the grain would have a lot to do with the strength of the bracing's effect on the entire structure.

You have a good idea there, but I suspect the reality would not meet the expectation.

[rule18]

Originally Posted by Mike McLenison

What if tops were cut out of half inch spruce (for example) and CNC milled so the bracing was wasn't glued but part of the original top? They would never come loose and would be a perfect part of the top. More expensive probably but better structurally and tone-wise?

At 1/2" thick, that top wouldn't be able to move with the vibrations, I think this wouldn't work as intended. Also, what's that guitar going to weigh?

[Tannin]

Cole Clark has done this for the last 20 years or so. They don't eliminate the bracing, but they can use very light bracing on both the top and the back. Also, the CNC system routs shallow channels for the bracing to sit in - it's slightly recessed into the top (or back) in other words.

I'm sure that plenty of others do something similar.

Carved tops and backs are not a new invention, they have been around pretty much forever (going back before the guitar was even invented). The difference is that modern CNC makes it practical to carve a top or a back very, very accurately for not a lot of extra cost - compare with the time and skill required to do it by hand.

There are other ways to reduce bracing. Moving the sound hole off to one side takes away a big design weakness (putting a hole exactly where you need the most strength) and allows for a lighter structure without losing strength. Quite a few makers do this.

Another technique is to borrow a principle from people who make other lightweight, durable, high-strength wooden structures like racing dingies. Take two very thin pieces of wood and hold them a set distance apart with something very light, such as end-grain balsa or poly foam. The strength is about the same as a single sold piece, and the weight about half. It is a standard technique in racing yachts and is also used for guitar, where it's called a double top.

Another version of the same idea is to make the braces the same way - out of, for example, end-grain balsa and carbon fibre. There is a chap in my home state who hand-builds guitars that way (which is where I first heard about it). One of these days I'll telephone him to as about his prices, but I suspect that if you have to ask the price you can't afford it.

[Steve DeRosa]

Originally Posted by RP

Better tonewise? Highly unlikely....

Originally Posted by rule18

At 1/2" thick, that top wouldn't be able to move with the vibrations, I think this wouldn't work as intended. Also, what's that guitar going to weigh?

As I recall, back in the '80s/90s Yamaha made a top-of-the-line L-5CES style carved-top jazzbox using this method. If you're not familiar with the process by which fine archtops are made, it involves carving and graduating the thickness of a 1-2" thick slab of wood, so that the final result is substantially thinner at all points (not to mention substantially lighter) - and although I've never personally played one, I understand the Yamaha archtop was fully competitive with its more-illustrious counterparts from Gibson and Guild...

[hubcapsc]

Originally Posted by rule18

At 1/2" thick, that top wouldn't be able to move with the vibrations, I think this wouldn't work as intended. Also, what's that guitar going to weigh?

I'm pretty sure he's suggesting that the billet of wood you'd start out
with would be that thick and it would be cnc-milled down to a normal
top with normal bracing - except the braces would be the same piece of
wood as the top instead of glued to the top.

-Mike

[JMFingerstyle]

Originally Posted by Lost Sheep

I suspect the direction of the grain would have a lot to do with the strength of the bracing's effect on the entire structure.

You have a good idea there, but I suspect the reality would not meet the expectation.

I think you hit the nail on the head. The grain of the braces needs to be oriented differently to the grain of the top, or the braces wouldn't add much strength at all.

[Corndog]

Originally Posted by hubcapsc

I'm pretty sure he's suggesting that the billet of wood you'd start out
with would be that thick and it would be cnc-milled down to a normal
top with normal bracing - except the braces would be the same piece of
wood as the top instead of glued to the top.

-Mike

I think Rule18 misunderstood the idea.

Milling the bracing from a billet of wood would have the grain coinciding with the top's grain direction. The conventional way of gluing the bracing to the top has the advantage of running cross grain to the top, which undoubtedly will be stronger and more stable.
I wouldn't be at all surprised to find that the "one piece" top will be more prone to cracking.

[hubcapsc]

Originally Posted by Corndog

I think Rule18 misunderstood the idea.

Milling the bracing from a billet of wood would have the grain coinciding with the top's grain direction. The conventional way of gluing the bracing to the top has the advantage of running cross grain to the top, which undoubtedly will be stronger and more stable.
I wouldn't be at all surprised to find that the "one piece" top will be more prone to cracking.

You can see that in this picture...



-Mike

[tadol]

A very good luthier, Dimitri Tenev (DMT Guitars), did at least one guitar that was modeled as a “reverse archtop” - the top was flat, so it appeared as a normal flat top guitar, but the inside was carved rather interestingly - sorta of as described by OP. It sounded quite good, but the material cost (the thickness required to create the top) and labor (which could possibly be reduced by automated equipment) made the guitar a bit pricier than most would pay. It’s very possible, but there are other issues involved that make it less likely to be anything more than an intriguing non-commercial alternative -

[rule18]

Originally Posted by Corndog

I think Rule18 misunderstood the idea.

Milling the bracing from a billet of wood would have the grain coinciding with the top's grain direction. The conventional way of gluing the bracing to the top has the advantage of running cross grain to the top, which undoubtedly will be stronger and more stable.
I wouldn't be at all surprised to find that the "one piece" top will be more prone to cracking.

I think I did misunderstand the idea, but it wasn't overly clear, either...

[Taylor Ham]

Some violin makers tried this in the 19-20th century as a cost or time saving measure. It didn't work well. It also wouldnt be an efficient way to increase the stiffness across the grain to where it needs to be for an acoustic. Interesting thought though.

[Rukulele]

I know of a ukulele builder who does this exact thing. Bonanza ukuleles. Never played one but I saw a couple of favorable reviews from gotaukulele.com (also on YouTube).

[Silly Moustache]

Surely what we are discussing is effectively what the early gibson archtop guitar designs were all about. A fair number of which are still around.