Acoustic Guitar Construction

kencierp wrote: I have not varified but I understand that Wayne Henderson does not even have a radius dish in his shop.

FWIW...this is true...he does not. he has a series of radii bars he uses with a clamping device built for him by a friend or family member, can't remember which. I have a pic if I can find it.

This is not Kosher I suppose, because this is a "Top" posting area...I have more about the top I will add it here as soon as I can...but...
Here is a fairly comprehensive explanation of the method John Arnold uses and from what Wayne Henderson told me in Denver 3 or so years ago, he came to the same conclusion while repairing many Old Martins when working for Gruhn years ago....and why neither use sanding discs.

Arnold direct Quote:

" I use side profiles from prewar Martins, and they don't have enough 'rise' in the waist area to produce a spherical arch. I have checked the back arches on many prewar Martins, and I have yet to find one that has a true spherical arch. They generally have the most curvature across the waist area, less curvature across the lower bout, and even less curvature longitudinally.
If you look at modern Martins, you will see what I am talking about. Virtually all modern Martins have a much more pronounced longitudinal curve in the back when viewed from the side. This is because the sides are deeper in the waist area, necessitated by the increased curvature produced by the concave sanding disc.
If you don't have a new Martin in hand, you can look at the side views of new Martins on the Martin website.
Martin used to bevel the kerfing to match the back curvature by using a block plane. An arching template is laid across the kerfing to 'eyeball' the arching angle. I still use this method, because I don't believe in the spherical arch, for several reasons.
Here are the radii that I use:
Top = 25 feet
Back, longitudinal = 20 feet
Back, lower bout (wide braces) = 18 feet
Back, waist brace = 15 feet
Back, upper brace = 25 feet
This produces a 'fair curve' when coupled with older Martin side profiles. The back is fairly flat in the upper bout, which results in more stability for the neck block."

John

That's not to say that the modern arch doesn't work, obviously it does. And with what little I know about it, I would say the arch, or sanding disc is easier to do...
Anyway, don't get me wrong, I'm sure no expert here...far from it, just thought I'd share what little bit I have been told by those who have done it differently and succeeded.

Here's Arnold's theory on the top radius and attachment...just for discussion...again, I have no clue...just sharing.

Question:
"They use the exact same tops (with the 25 ft radius bracing) and glue them to a flat plane rim. You now have to force the top to adapt to the different shape. This will cause extra stress (I think they even call it "pre-stressing";) . I would expect that this extra stress will cost bass response. "
--------------------------------------------------------------------------------

John:
I have always used this technique. It is MHO that this pre-stressing is a temporary effect that is minimized a short time after the guitar is strung. Besides, all arched backs are 'pre-stressed' when they are glued to the body, since the cross bracing does nothing to generate a longitudinal arch.

Question Quote:
--------------------------------------------------------------------------------
they claim that these guitars sound MORE bassy, and closer to the original Martin sound. I'm not saying this can't be true, but if it is true, I would like to know the physics behind it.
--------------------------------------------------------------------------------

John:

"Simply because a true spherical arch is more resistant to vibration. This is the primary reason that I don't prefer the profiled arch around the perimeter of the top. The guitars I have played that have that construction are too stiff and lacking in bass response. I think that the best vibration occurs when the edge of the top is in a single plane. I do bevel the kerfing, particularly in the waist area of the tight-waisted shapes. But I have found that with the small amount of arch that I use, very little beveling of the kerfing is necessary on dreadnoughts.
Another arching tip that I have mentioned before is the asymmetrical top arching that I use. This is done to counteract the torque that the bridge applies to the top. My braces have a 25 foot radius arch, except in the area below the bridge (lower bout). In that area, my braces are perfectly flat. This results in a bridge that is slightly "tipped back" when the guitar is unstrung. With tension, the torque on the bridge will rotate it, making it level with the plane of the edge of the top. IMHO, this produces the best chance for vibration."

John

John has interesting opinions and conclusions -- "take with a grain of salt" unfortunately some of the statements regarding Martin's simply do not jibe with my reaserch. Also, I would take exception to the premise that the old hit and miss method of radiusing the back of the rim is somehow better than the consistent procedures used today. Such as:
The back is fairly flat in the upper bout, which results in more stability for the neck block."
This is "bull" of course a poorly executed sanding job will result in less stability (mis-matched glue joint) --- not whether the back is flatter or a true spherical shape.

I will point out that until the dawn of the cutaway (which is fairly recent) Martin did little in their process to prevent some 14th fret fingerboard hump -- pinching the FB extension down was an accepted convention, the heel fit to the rim was the main concern. Did that poor procedure make the old Martins better guitars? Most everything in our lives is touched and improved with progress from better ideas of the next generation --- I could not possibly buy into the notion that the pinnacle of "guitar making excellence" was reached 180, 100, 50 or even one year ago. I look at it a little different --- it is amazing that fine guitars were produced with the primitive technology of years gone by, thankfully even we in the small shop now have accurate, affordable tools, fixtures coupled with free flowing information so we too can produce fine instruments $.02

Prior to this posting I've read those statements of John's many times over and have come to the conclusion that it would be difficult at best to tell a difference in sound using those methods and I certainly don't think the time and effort to get it right is worth it.

I've also thought about the comments/opinions of the "pre-war" Martin's having the best sound ever and believe it is in part due to at least to factors:

1. aging and playing in of the wood and
2. survival of the best i.e. who wants to invest in keeping a crappy sounding guitar around, even some of the old Yamaha Nippon Gakki guitars sound pretty decent.

I don't think much of that has to do with the radiusing of the guitar braces (but I could be wrong).

kencierp wrote:John has interesting opinions and conclusions -- "take with a grain of salt" unfortunately some of the statements regarding Martin's simply do not jibe with my reaserch. Also, I would take exception to the premise that the old hit and miss method of radiusing the back of the rim is somehow better than the consistent procedures used today. Such as:
The back is fairly flat in the upper bout, which results in more stability for the neck block."
This is "bull" of course a poorly executed sanding job will result in less stability (mis-matched glue joint) --- not whether the back is flatter or a true spherical shape.

I will point out that until the dawn of the cutaway (which is fairly recent) Martin did little in their process to prevent some 14th fret fingerboard hump -- pinching the FB extension down was an accepted convention, the heel fit to the rim was the main concern. Did that poor procedure make the old Martins better guitars? Most everything in our lives is touched and improved with progress from better ideas of the next generation --- I could not possibly buy into the notion that the pinnacle of "guitar making excellence" was reached 180, 100, 50 or even one year ago. I look at it a little different --- it is amazing that fine guitars were produced with the primitive technology of years gone by, thankfully even we in the small shop now have accurate, affordable tools, fixtures coupled with free flowing information so we too can produce fine instruments $.02

Ken, you obviously know much more about this than I do...OR probably ever will know and I really appreciate that!
You make a lot of sense and clarify many questions along the way, with so much scattered information it can get pretty darn confusing for a "Newbe".
It hasn't been very long ago that gleaning any information about this highly prized and sought after endeavor was next to impossible.
I have played guitars of both of the builders (Copiers) mentioned, Wayne's #400 (About 2 years old at the time and a really nice little 00 he made for a friend.
I played one of John's dreadnaught's that was about 5 years old, all were great sounding quality made instruments that captured "That sound" of long ago.
One thing I DO know, is the above statement about sound is totally "SUBJECTIVE"...however they must capture the imagination at least of some, or there wouldn't be the constant demand for their instruments....so go figure.
Thanks for your patience with child like statements or questions...I'll keep learning and maybe someday I'll be able to put one together that I can enjoy before I fall over... :>)

Ben-Had wrote:Prior to this posting I've read those statements of John's many times over and have come to the conclusion that it would be difficult at best to tell a difference in sound using those methods and I certainly don't think the time and effort to get it right is worth it.

I've also thought about the comments/opinions of the "pre-war" Martin's having the best sound ever and believe it is in part due to at least to factors:

1. aging and playing in of the wood and
2. survival of the best i.e. who wants to invest in keeping a crappy sounding guitar around, even some of the old Yamaha Nippon Gakki guitars sound pretty decent.

I don't think much of that has to do with the radiusing of the guitar braces (but I could be wrong).

I'm sorry Tim, I didn't intend to "Hijack" your thread...I suppose I misunderstood the posting, not unusual for one over 70 :>)

The heading does say "Bracing Radii" and I thought the inclusive information was relevant:

Top = 25 feet
Back, longitudinal = 20 feet
Back, lower bout (wide braces) = 18 feet
Back, waist brace = 15 feet
Back, upper brace = 25 feet

To ME it was interesting, considering I had thought all along that it was a constant 25" or 52" or 16" or 15" or what ever for either the TOP or back depending on who you see in print or talk to or come across...the rest was just the inert ramblings of an "Old Man" ...I'll try to be more careful next time Hahaha.

Ray :>)

Ray -- nothing childish here -- just some information sharing. I happen to comminucate and glean information from two of the premier vintage replicators in the country, Preston Thompson and John Grevens and as you mention these guys can command much $$ for their works -- the rub with me is the claims of the vintage "silver bullet" in construction process, materials, glues, chemicals or even dimensions. That can be purely reaching and marketing of one's self, ideas or products. If Preston and Grevens are producing highly acclaimed vintage quality and sounding instruments and not using Arnold's premise or ideas --- how is that explained? Luck? Or more to the point that some things simply do not matter? I think Grevens has it right -- good material, build it light and build it tight and clean and you'll end up with a good guitar. As a side bar, over at one of the other forums a guy tells of his encounter with Wayne Henderson at some show -- he asked Wayne to play his Walnut OM that he had built, and give him an opinion --- so Wayne did, the guy was thrilled because Wayne did not want to put it down -- just happened to be a KMG kit, that was built light and tight.

Ray, I didn't think you hi-jacked the thread. Hope you didn't mis-read my intent. I found John's comments interesting, I have a lot of respect for him but I still question the processes he was discussing in that thread. That's why I read and re-read it so many times.