Overview: In 1965, Guild used Brazilian Rosewood for the back and sides of its second largest 12 string, model F-312. It has a full 16" lower bout, but a narrower waist than a standard dreadnought, and the waist is closer to the top. This project came to me as parts, conveniently packed in a squarish box. The finish had been stripped off everything but the top and the top had been seriously damamged when the original bridge (not included) was removed. I discussed my prospects with a local dealer in vintage guitars and he said, with that much original finish (and other parts) gone, there was no use in "restoring" but rather leverage the advantages intrinsic to the aged Brazilian to create a refurbished modernized version of the F-312.
Necks get a lot of stress over the years, especially on a 12-string. This one had suffered much. Its male dovetail no longer fit the female dovetail in the body, so that it raised the action of the strings way high. Both sides of the joint had problems. While it was nicely laminated from two pieces of mahogany and a middle strip of maple, the three peices had delaminiated from each other in the headstock area. The headstock was overlaid with a soft plastic face which contributed nothing to the overall strength of that portion, so it had bowed up as well as severely cupped. There were two one-way truss rods embedded into the neck which appeared to be frozen (which I have freed).
This required that the delaiminations be reguled to start. Then I clamped the up-bow into a reverse bow, heated that portion with a heat gun, and left it clamed up for three months. That cured the up-bow but had no effect on the cupping. There was no choice except to plane and sand that problem flush and square. This removed the serial number (AS-141) which had been stamped on the back of the headstock. It also thinned the headstock so that it would be even more susciptible to warping in the future, if I were to simply reattach the soft plastic face plate. So I have reserved a very thick "veneer" of ebony to use for this purpose. And I will add a layer of maple underneath it. Since the stamped serial number on the backside is now gone, I will also laminate a double layer of veneer on the back as well. I have a new Guild logo in gold pearl ready to inlay into the ebony face.
The doevtail joint has been refit, so that the neck angle is now correct. Since glued dovetails inevitably fail, this will become a bolt on neck, with the fingerboard glued to the top with easily removed hide glue, if and when it needs another refit. Since there will be an addition to the top block that extends it all the way to the sound hole, the "sandwich" of fingerboard, top, and extended top block with further discourage the negative effect of string tension on maintaining a stable action. This amounts to adding very little weight, and the weight will be added to a region of the top that contributes virtually nothing to the top's movement.
The back came with a drying crack that runs from top to bottom. A piece of veneer with grain running parallel to the crack had been glued over it, to repair. But it too had split, as would be expected. Further, some very heavy mahogany replacement braces had been fit, while the fourth remains empty. The back itself is a fine piece of Brazilian that is quite live when tapped. Since the "patch" must be replaced anyway with one where the grain runs across the split, new braces will be fashioned, thinner, taller, and lighter. I am inclined to use spruce for making them. There is no sense in damping out one of the instrument's greatest assets, its well aged, straight-grained, quarter-sawed Brazilian back that seems very responsive. If I get brave enough, I'll sand it a little thinner.
There were several wide, but repairable drying cracks in the top. And it was cut too rift for my taste. But the most troubling aspect was the large amounts of tearout where the original bridge(s?) had been removed. After fiddling around with various "fixes" that did not work out like I hoped, I removed the top. Some will no doubt find this bordering on an immorality. But I have potentially better tops in stock, in particular, a red spruce top from the Ted Davis stash, that "poings" wonderfully and is cut from a split billet with absolutely no runout and is perfectly quartered. This top is probably 30 years old since the billet was cut from the tree. I consider this to be at least a valid refurbishment, if not hot-rodding the top spec, which will be a little lighter than the original. (Like remodelling a house, this project has expanded way beyond initial expectations.)