An interesting construction log

[Dave Bagwill]

I like a good construction process in pictures. Here's one I ran across yesterday:
http://www.defaoiteguitars.com/page39.htm

[ken cierp]

For the most part very nice -- however I do not see or understand any logic especially engineering for that honk'in huge cantaleveried extension on the neck block. It has no chance of stopping/preventing the folding of the neck toward the soundboard which will happen no matter what over time -- its really the shrinking of the top (downward belly) which distorts the entire instrument -- best defense --- proper humidification.

[Dave Bagwill]

Yeah, I was looking at that also and wondering if there was any value to it.

Let me ask this: are the CF rods from the neck block to the blocks on the sides really doing anything? I keep thinking about 80 year old Martins that were 'primitive' according to some of the modern 'advances'.

[ken cierp]

I'd have to say that the presumption with the cf rods is that the rods not only prevent the top from being push down by the fingerboard extension (huh?) but also some how it prevents the back plate from stretching (think about that is that happening?) From my own experience each and every guitar I repaired or even looked at with a neck that appeared to bow forward had a concave soundboard -- caused by bridge roll from lack of humidity or too high of tension string -- neither aliment would have be prevented by CF rods. $.02

[John Link]

Dave: Some of the Martin histories I've read say there were structural problems with those 80 year old Martins that brought them back to the factory for repair too frequently. In the old days, they say, there was no specific repair department, so when a non paying repair job came in, people that normally worked on new production that payed, were diverted to execute it. I am not a Martin historian but I understand in general that the bane of small business is performing work for free after the sale is completed. Too much of it and you are toast.

Thus, these stories say Martin gradually beefed up bracing - to the detriment of sound. On the other hand, the same logic suggests Martin would have solved their neck reset problem by now too. Have they?

I've seen the carbon fiber "flying buttresses" in a lot of builds. They mystify me. I don't think they hurt but can't testify to that. His contention that the upper bout contributes to sound can be justified because it contributes to the total volume of air enclosed by the body. And the parts will vibrate before they are assembled. But even the lightest built guitars - the Harmony 1260 is a great example - tap out dead once you get above the waist. Enclosed air volume is always a factor but plate vibration "up there" does not seem to be, no matter how it is built.

The problem you see with the 1260s is always a neck angle problem - caused by the usual suspects, starting with a poorly fitted dovetail when the instruments were built. But the soundboards don't collapse, the sides don't deform, the backs do not stretch. The joint simply destabilizes and becomes a slow motion hinge. Truss rods also break, perhaps because people attempt to use them to fix the dovetail joint problem, which they can't.

Ken, the guy has some other sections on his site that explain the fingerboard-extension. He does not believe in gluing the fingerboard to the soundboard, wants it to pivot with the neck. Thus it needs a way to remain stable with respect to the neck which pivots off the two-bolt-secured vertical joint that attach it to the body.

John Mayes and (I believe) Taylor use a fingerboard-extension as part of a scheme to bolt the neck to the body in both the vertical and horizontal planes, rather than using glue for the horizontal. It requires something like the neckblock-extension shown in this construction log as the mating surface for the horizontal connection. Their idea generally appeals to me because it makes neck resets extremely simple, and makes the fingerboard-extension / neckblock-extension into a substitute for gluing the neck to the soundboard. It also affords some wiggle room in the construction process for initial action setting (some might call it mistake resolution).

There is a consensus that as a steel string guitar ages, the neck-body joint is one of the places where the ravages of time seem to converge. The idea to build it "solid" in the first place has its appeal, but may not be practical in an acoustic instrument. Thus, prudence leans me in the direction of making it easy to adjust this joint as the instrument undergoes the effects of aging.

I would love for someone to conduct double blind "sound quality" tests of the traditional dovetail with glued on fingerboard versus a joint well engineered for future maintenance AND present solidity.