If you’re thinking about making a curved guitar case, maybe I can help talk you out of it.
1/2″ ‘Mahogany’ plywood, the lightest I could find locally. Most plywood doesn’t respond well to steam bending, so I cut kerf slots every 3/16″ along 5″ x 48″ rips of plywood. I did not kerf the final 2″ of each end to allow for joining the sides together with 60 degree scarf joints. Standard OM size cases are roughly 9′ in circumference, so 2 1/2 rips were needed. The plywood is very bendy after kerfing so the tight bends are no problem, but they are also very fragile and the short end grain tabs break off easily.
I initially made an inside form, but quickly realized there would be no way to effectively clamp and epoxy the kerf’d plywood case sides. I used some leftover OSB plywood to make two pattern forms, then made up the 5″ case thickness with some spacers. The kerfs allow the use of mason twine for clamping (taut-line hitch knots), with bar clamps only needed for the seams. There are 3 seams, two in the neck area, and one at the end pin location (I goofed on the end seam and cut the same scarf joint twice, so had to made a beveled glue block for the end, you can see the block resting on the form at the top of the photo above).
I used West System Epoxy with speed set catalyst, which let me coat one side and flip vertically for the other side after one hour without sagging and without flashing over. First coat was thickened with colloidal to help fill the saw kerfs for more strength. The two last coats were over fiberglass reinforcement. There’s a green tape boundary on each side of the form, it acts like a dam to keep the epoxy from sagging. Once cured, the twine was cut away and the epoxy was scuff-sanded so contact cement will bond to it.
The sides of the case came out very rigid. It doesn’t feel very heavy yet, but weight is probably going to be a problem. The case top was formed and epoxied like the bottom.
Clamping the case ends. 1/4″ plywood was used, cut oversized and and trim routed after. Since the side pattern isn’t perfectly symmetrical, it helps to clamp both sides components together before gluing on the panels. I applied epoxy to the margin of the panel first, set the sides in place, clamped them to the panel, then applied a epoxy fillet (thickened with colloidal) around the perimeter.
Fabric selection was both amusing and horrifying. It’s always fun to pick campy materials, but costs these days are horrifying. I found some fake gator pleather. Easy to apply with contact cement, just have to cut many, many tabs for the turns. Separate pieces were cut for the sides to tab over into the interior of the case.
The lid needs a continuous lip to interlock with the case, and a matching rail on the bottom to balance the dimensions. I found some flexible drywall corner bead and cut this into strips and wrapped it with pleather. It needs to be attached with strong thread ( I used waxed saddle thread) so I covered each strip with tape to tick off the drill holes for the stitches. I did a locked backstitch. I only drilled 6″ of holes at a time, removed the tape before stitching, repeating the process around the top and bottom.
Hardware needs to be installed before the interior fabric. Hardware options are paltry to say the least. I ended up having to make hinges because all of the hinges I could find looked really flimsy. I ordered a handle, but the bosses and handle attachment points were chrome plate plastic, so I made new ones. The aluminum parts I made don’t match the chrome clasps I installed, but it’s not too jarring. Due to the thickness of the lipping, I shimmed out the clasps and hinges on the bottom with black ABS. For fasteners, I used 6/32 threaded inserts in the 1/2 plywood for the feet and bumpers, and 4-40 machine screws with lock washers and nuts recessed in the inside of the case for the hinges and clasps. The handle bosses are internally threaded to 6-32 as well. All threads were dabbed with Loctite blue before assembly. The only wood screws I used were for the neck compartment partitions, which were screwed in place with #6 with finish washers (with doubled-up flat washers underneath to prevent cutting the fabric).
The inside fabric was surprisingly easy to do, but it would be much too tedious to describe in any detail. Pretty easy to figure it out in progress, working from the panels up to the sides. I leave enough margins on the panel upholstery to be able to tuck in the side cushioning. As for materials, I used black velour and 3 types of foam, dense foam mat (gym mat tiles), 1/2″ craft foam, and high loft batting. I used dense foam for the top, with a layer of 1/2″ craft foam over that for the bridge-to-nut cushion. The bottom has dense foam under the body, with a layer of the batting over that. The sides in the body compartment use 1/2″ foam, with voids in the foam at the end pin and pickup control panel. The foam ends at the compartment, the remainder of the sides are just doubled up velour. I used contact cement (spray and can) for most of the fabric, but used double sided carpet tape to attach the side cushioning because it’s much less messy to work with.
All in all, this was a conspicuously intensive project, in both time and resources. Expensive and tedious, but fun, and not wholly without merit. I wouldn’t have done it if I didn’t already have the plywood and epoxy. Even so, it was more expensive to build this than to buy a fitted case from the guitar manufacturer. But I like the finished case. It’s heavy but strong. If I could do it over, I’d either try to find some lighter-weight plywood, or figure out a way to just form up the whole thing with fiberglass.