Faux tortoiseshell pickguards made their first appearance in 1959, when most (but not all) Fender instruments were fitted with multi-ply pickguards made of celluloid (cellulose nitrate). The Jazzmaster received four-ply pickguards with a faux tortoiseshell layer on top of the white, black, white layers.
Celluloid had some drawbacks however. Over time this particular material was prone to shrinking, warping , and cracking. Today you can see many old Fenders where the pick guard screws are angled inwards, the pickups are “squeezed” by the pickguard and cannot be raised or lowered any longer, or the tip of the pick guard has been broken off.
Consequently, Fender switched to less temperamental plastics for its multi-ply pickguards around 1965. The faux tortoiseshell top layer of these improved pickguards, however, remained celluloid, which originally presented a problem: As the celluloid faux-tortoiseshell layer inevitably tried to shrink, it would warp the non-shrinking plastic layers beneath it into a bowl shape. Fender designers of the 1960's compensated for this troublesome tendency by increasing the number of pickguard screws, which did the trick.
Here is a very cool 1966 Fender Jazzmaster which has some of these symptoms.
The pick guard has curled up beneath the bridge, as it shrunk back over the bridge post grommets.
The aluminium shielding underneath has been exposed in places, and the screw holes through the pick guard no longer align with holes in the shielding. A number of screws are angled inwards and a couple no longer have any grip (one is right on the edge of the control cavity and so has nothing to hold it in place).
The pick guard has pressed inwards against the pickups, preventing them from being adjusted. The output of the neck pickup was considerably louder than the bridge. The pickups volume could not be balanced as it wasn't possible to raise the bridge pickup.
Through some sympathetic work it was possible to get the pickups working again, relieve the strain that the screws were placing on the pick guard, and sort out the loose screw situation. It was important not to make any material changes to the originality of the guitar, so the adjustments were subtle, but enough to get the guitar fully functional again.
First I made a sketch of the affected cavities and noted where the pick guard was tight against the pickups and misaligned with the bridge post grommets. This was to ensure no unnecessary filing or scraping was done on areas that didn't need it , but focussed on the areas that did.
Here are pictures of the original pots, with codes 304 6515, dating them to 15th week of 1965.
Removing the screws from the pick guard (except a couple of good screws to keep everything in situ), the position of the misaligned holes were marked on the aluminium screen.
The electrics were removed from pick guard, separating the pick guard from the aluminium screen. The holes in the aluminium were widened to line up with the hole positions in the pickguard..
I made a plywood backing, with cavities cut out, to which the pickguard is screwed down to prevent it from shrinking further (if left unsupported it will continue to shrink in the direction it’s been wanting to go for the last 50 years).The plywood also serves as a backing template through which it will be easier to scrape and file the pick guard cavities.
I then carefully scraped and filed the pickguard in the appropriate areas, blending the edges so that the work wasn’t noticeable, and making several test fits back on the guitar to check progress and ensure the minimum amount of material is taken off.
Once the pickguard is refitted the worst misaligned holes (there were 4 of them) were carefully marked, drilled, and plugged with 1/8" hardwood dowels. The holes were then redrilled so the screws could go in vertically.
I shaped and glued a small piece of mahogany to the side of the cavity so the screw can grip onto something and not remain loose in the hole.
Everything is put back together. The pickups can now be raised and adjusted for a balanced output. There are no loose screws, the worst affected screws now align straight relieving stress on the pick guard, and the aluminium shield no longer pokes out from under the pick guard.
A not uncommon mishap that can befall an acoustic guitar is where the bridge becomes loose, or even snaps completely away from the body. When tuned to pitch terrific string tension pulls on the guitar top and bridge and so it is essential that there is a strong glue joint between these components.
There are a number of reasons that a bridge can come loose on an acoustic guitar - an improper or poor glue joint, low humidity or heat, loose braces or other structural issues inside the guitar putting undue strain on the bridge, or a combination of these.
Typically a bridge will come loose along the back edge, forming a gap between the guitar top and the bottom of the bridge. This may be difficult to see and not obvious so a good way of testing to see whether there is any gap under the bridge is to try and slide the flap of a guitar string packet underneath. This will determine the extent to which the bridge is loose.
If the bridge is loose it is usually preferable to have it carefully removed ( I use heat blankets specially designed for this job) and have it re-glued properly, rather that running the risk of the bridge suddenly giving way under string tension and damaging the top in the process.
In the example below, the bridge snapped clean away from the top, taking chunks of the spruce top fibres away with it. Here's how I fixed it.
The old glue and fibres left on the bottom of the bridge are carefully scraped off so that a clean gluing surface remains. You can clearly see a ledge all around the perimeter of the bridge where no glue was applied during manufacture (quite common on lower end, and less expensive, acoustics). This lessens the overall gluing surface and makes the joint weaker than if the whole bridge was glued down.
A big lump of spruce stuck to the bottom of the bridge was removed and used to patch the top in its original position between the G and B string holes. Luckily the damage caused when the bridge came away wasn't too severe in this case, it could have been worse.
Here the spruce patch is glued and clamped, and the result.
The footprint of where the bridge sat on the top shows a ledge of lacquer around the perimeter. The lacquer is carefully removed to provide for full contact with the bridge, and a flat and even surface when the bridge is glued back down. All the old glue is removed from the top and any remaining gaps in the spruce filled or patched and then sanded flat to create a level gluing surface.
Bridge footprint with lacquer removed and holes filled, ready to be finally sanded and scraped flat in preparation for gluing.
The bridge is located in the correct position and held in place, ready to be glued and clamped. When the bridge is clamped, a caul has to be custom made to go inside the guitar and over the top braces to protect the delicate top from the strong clamping pressure, by spreading the load. Any glue squeeze out from clamping is cleaned up before the glue drys.
The guitar is left clamped overnight for the glue to dry. Any remnants of dried glue in the bridge pin holes are then cleaned out. The guitar is ideally left for another day or two before stringing up to pitch.
The bridge transfers the vibrations of the string through the top so good coupling between these elements has the added benefit of improving the tone of the guitar. Job done!