Mold for Carbon Layup
vacuum & pressure
The pattern was then taken to a fiberglass mold maker. They covered it with mold release and sprayed it with gel coat which is like a really thick paint. This surface is very shinny and smooth against the pattern side. After the gel coat cures enough, the mold is sprayed with a chopper gun that outputs resin and fiberglass mixed together. Also a fiberglass mat is applied with a roller to expel air and excess resin. The final result is shown above with a reinforcing frame to maintain it's shape.
I did a lot of sanding on the orange with increasingly finer sand paper. I then dropped it off at the composite company. Even though my mold was several years old it still needed a post cure in an oven to cure unreacted resin and to set it's final shape. The smell of styrene was nasty. They touched up my sloppy work and coat it with a secret mold coating. The prepreg resin coated carbon fiber was cut and laid into the mold. Bleeder and breather materials were applied and a bagging material was placed over the lay-up. A vacuum fitting was installed. The entire mold and materials were place in a autoclave which is a pressure vessel like a pressure cooker (but no water allowed). It is then heated to 250-350 F at 100 psi. The heat and pressure was increased and decreased in a very controlled manner to prevent warpage of the part and mold. The part was removed from the mold warm to make the demolding easier. After the part was trimmed it was returned to me with a panel of composite materials for the top of the body and the head stock.
I purchased a fret board from a guitar supplier. I glued the fret board to the edge of the neck and covered the body and head stock with the composite panel. I used my pick guard from the JEM was a template for the cut outs. The normal pockets front and back were considered unnecessary. Tremelo inserts were glued in and a block for the springs and claw. That is were it stands to date. As it stands now I have more than $3,000 invested without considering my labor. The project it about 10-12 years in duration to date.
Technicians cutting and
assembling carbon prepreg
Another path of manufacturing is to digitize a guitar and create a CAD model (right). That model can be used to create CAM tool path using a CNC machine that will create a pattern like the one on the upper left. This process is much more accurate than by hand and very much more expensive than the way I'm doing it.
Chopper Gun fiberglass+resin
There are a ton of issues in this process. The learning curve is huge. I've spent 25 years learning composite technology and theory. I started this journey while I was in the prosthetics field (artificial limbs). My main focus was the socket that connects the limb components to the patient, but being a typical musician I wanted to know how to build a guitar out of composites also. The guitar I am revealing here is my 3rd attempt.
The first item needed is something to make a mold off of. In my first attempt it turned out to be Squire Strat that my son didn't need any more. In the case of an acoustic guitar and my JEM it was a from scratch. The biggest issue with mold making is getting the composite part out of the mold. Mold release agents and proper shaping of the mold are of primary importance. A draft angle is the amount of taper for molded or cast parts perpendicular to the parting line. Next time you get a cup at a fast food place you can see this principle at work. Imagine that the mold for the cup has to have a draft angle inside and out for both mold sections so the part will release easily.
The first thing I did was to get some high density urethane foam. This was easy to shape and coat. The first part is called a pattern. I traced my guitar and rough cut it to shape. Then I sanded and shape the final shape by hand. I had a mold maker at the composite company do the final shaping to make sure draft angles were proper. I then had a paint shop sprayed it to create a smooth surface. I also had them paint my JEM "71" Chevy Nova" blue which is my color. I then mounted pattern to a coated particle board frame. This creates a return that extends past the edge of the finished part for stability and a surface for cabon to extend past the edge of the part.
Carbon Copy Guitar
Large oven with
Pattern with reinforcement frame