making an ultra-light archtop.

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Brian Evans
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making an ultra-light archtop.

Post by Brian Evans »

So I was reading in a magazine, I think Fretboard Journal, about a famous luthier whose latest deal is using what I call flying buttresses to support the neck block and take the stress of the string tension completely off the top and transfer it via carbon fiber rods to blocks glued to the sides at the waist. So I was thinking about how this idea might translate to an archtop. In my view the arch of the top is there, from a structural point of view, to support the downward load of the strings onto the peak of the arch, and to carry the tension of the strings between neck and tail block. Lets say the downward load is 40 pounds and the tension is 200 lbs. Lets say we already know that the top thickness at the recurve is 1/8" and that carries the downward load of the strings just fine. The tension of the strings is carried by the thickness of the center of the arch, in my guitars around 1/4" to 5/16", and by the back arched plate, a little thinner but hardwood, and by the bracing of the top plate. Let's say we build either a triangulated buttress situation, or simply build a longitudinal brace inside the body to tie the neck and tail blocks together and take all of the load of the string tension off the top and back. Why couldn't we carve the top to a uniform thickness of say 1/8" (still thicker than a flat-top top and with the built-in added mechanical strength of the arch), brace lightly either fore/aft on the centerline of the arch and side to side directly under the bridge, or maybe fan braced, and get a really light top and back plate? I wonder what would happen if you did that? Maybe even string it with nylon...

Questions rattling around in my brain...

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Barry Daniels
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Re: making an ultra-light archtop.

Post by Barry Daniels »

I built a flattop with flying carbon fiber rods supporting the neck block mainly just to minimize future movement that normally leads to the need for a neck reset somewhere down the road. That in no way allowed me to build lighter. It just adds some structure for stability. However, I've come to the conclusion that building extremely light is not a good direction for tone. Tone comes from having wood under stress being excited by vibrations. My guitars built with Somogyi's techniques were good but lacked mid-range tonal response. I am now using Trevor Gore's techniques in search of the full spectrum.
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Dennis Duross
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Re: making an ultra-light archtop.

Post by Dennis Duross »

I've been working on dometop (and back) archtops off-and-on for the last several years.

The arch of the dome is a little over 0.7" from neckblock to tailblock.

Solid beam of wood running from neckblock to tailblock.

Plate thickness of 0.12" and a single, 12" long x 0.3 x 0.6 brace running from the bass side of the lower bout to the treble side of the upper, running under the center line of the bridge.

This diagonal brace has made all the difference in the world in terms of really activating the top and opening up the bass.

So if I were inclined to do a carved top (which I'm not), I would be interested to do something to take up the tension induced by the string tension (which I believe acts as a stiffener for the top plate), and would try out a diagonal brace.

Michael Lewis
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Re: making an ultra-light archtop.

Post by Michael Lewis »

Steve Andersen has made some rather light weight archtops with a big bass response, and an oval sound hole in the upper bout. You might look into some of his well regarded work.

The dynamic response and tone of a "traditional" archtop is achieved by using traditional specs. By changing arching, plate thickness, bracing, etc. you will also change the dynamic response of the instrument. Get busy and try your ideas, then report here how everything goes. Just remember the luthier's mantra: the next one will be better.

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Randolph Rhett
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Re: making an ultra-light archtop.

Post by Randolph Rhett »

Mine are have carbon fiber soundboards and are extremely light weight. I can't remember the actual measurements, but my tops weigh about a quarter of my spruce tops.

Yes, that does change the sound and dynamics. I consider that a good thing. They are still arch tops with characteristic loudness, punchy mid-range, and good note separation. But they have a fuller tone and more "sweetness" (is that a thing?).

I'm cautious about seeming like I'm just self-promoting, but I posted a link to me playing the guitar on this post:
http://www.mimf.com/phpbb/viewtopic.php?f=5&t=4392

I hope that encourages you to experiment. I think there is a lot of room for tonal experimentation with acoustic arch tops. Go ahead and build yourself a better mousetrap!

John Morciglio
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Joined: Sun Feb 07, 2016 2:30 pm

Re: making an ultra-light archtop.

Post by John Morciglio »

Hello all!

First post here.
Joined a while back and I always lurk when I see "carbon" or Archtop discussion.

I have been building quite a while (80's) and lately have been building carbon and hybrid Archtops.

A few solid body electrics etc.

The full carbon builds don't seem (that) light when running 2 pick-ups?
Probably lighter than most?

Here is a couple full hollow Flat-top and Baritone Arch-top w/ wood necks. (necks all have full carbon stringers from front -to-back about 1/8" thick along with a truss rod.
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First time loading Images here so I will check?

JM

John Morciglio
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Re: making an ultra-light archtop.

Post by John Morciglio »

Pics are "fuzzy"?
Maybe I need to re-size here?
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Taking a break. Making a 6 guitar portable stand to do demo's :-)

Jason Rodgers
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Location: Portland, OR

Re: making an ultra-light archtop.

Post by Jason Rodgers »

Hi, John. I saw you post these on The Gear Page. On that flat top, is the lighter-colored soundhole surround part of the top structure, or just decorative? Cool stuff.
-Ruining perfectly good wood, one day at a time.

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