New adjustable mould

Since starting to build in a sturdy mould a couple years ago, I have not wanted to go back to free-form workboard building. However, I also did not want to build (nor would I have had room for) another heavy MDF guitar mould. I don’t know how many of these Torres/Fleta guitars I will build, and I do tend to like building guitars of different shapes and styles, so I figured that the best idea would be to build a space-saving adjustable guitar mould. I got the idea from a picture of a mould that Irish luthier Darren White (read my interview with him here) sent me a while ago. This mould will allow me to build guitars from small Torres shapes (including the SE117 size instruments that I have built in the past) to full size acoustic grand auditorium style guitars. I still have to add a neck portion to this mould, but I have not reached the stage of building where I need it, so that will come later.

The mould is made up of a work board base and 22 adjustable side supports.

I used a “scrap” piece of double-thick plywood to form the base of the mould. I had glued together two pieces of 5/8in G1S plywood a couple of years ago to make a makeshift side mould for a steel-string guitar. I was no longer needing this piece for its original purpose, so I cut out an oversized guitar shape to use as the workboard/base. I then cut 22 slots about 3/8 inch wide in towards the centre of the board all the way around (see image above).

The side pieces were made out of leftover G1S plywood from my bench top. I needed to make supports that were about 4 inches high (about the depth of most guitars that I build), and each support needed a 1/4 inch hole down the centre to accept a bolt. I decided that drilling these holes would take a long time and would never give me the perfectly perpendicular result that I needed, so I decided to rout square channels instead. I sandwiched two pieces of plywood together to make the support, but only routed a channel in one of the pieces. The asymmetrical result was actually desirable in this case. For efficiency, because I needed to make 22 of these supports, I routed and made 3 long strips of plywood sandwiches and then sliced the long pieces into the 4 inch lengths that I wanted.

Two of the supports needed to have a convex surface to allow for a smooth bend at the waist of the guitar, but otherwise, the supports were left square. I cleaned up all of the pieces on my belt and disc sander to make sure that the surfaces were smooth and square.

I then needed to rout a step in the bottom of each side support to allow for an overhang on the soundboard. You can see the step in the image above. This step is deep enough to accommodate a 1/2 inch overhang around the periphery of the guitar and will allow for the thickness of a guitar top and a cork shim without being too tight.

Then I fitted each side support with a 6 inch carriage bolt, a washer, and a wing nut. The bolts slide nicely in the slots that I cut into the workboard, and, when the supports are lined up to the outline of the guitar, and the nuts are tightened down, the mould is very solid and reliable.

Finally, for the wood part of this guitar, I screwed a scrap chunk of wood to the underside of the guitar (about 1 inch thick and 1.5 inches high) so that I could easily clamp this fixture into my universal vice.

Next, I made a cork shim to support the arch of the soundboard on this guitar.

And, voila! Here you can see the braced soundboard of the current build sitting snuggly in its new home:

This mould has some added benefits that I had not realized when I set out to make it. First, adding that hunk of wood to the underside was genius because the ability to have this sitting in my vice is amazing. Secondly, because all of the side pieces are removable, I can take out a few to have easy access to the top (for instance, when shaping or gluing braces) while still having the top secure on the board. Thirdly, if I do remove one or two of the side pieces and need to reach a clamp to the centre of the board, I can slide a cam clamp down one of the slots and can easily clamp braces anywhere on the soundboard. Finally, this mould is incredibly light! I do like my MDF mould, but it is really heavy and takes up a lot of room.

I’ll keep you posted on this mould as the build progresses and as I add other parts to this set up.

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