The collapsible acoustic/electric guitarBy Brent Waters

Composites have unique characteristics that can't be found in any other type of material. Due to this, I wanted to invent a product that utilized these characteristics and couldn't be made from any other material. I began to brainstorm on what I could make.

The design

I have traveled around the world and I always love having my guitar to play. The problem is that I need to carry it around through the airport, as well as check it in as a second bag. Even a travel guitar, which is small and less fun to play, can't be packed in my suit case. To avoid this, I decided to design a full-size guitar that can be broken down and packed into a simple carry-on suit case. This way, when I travel, I no longer have to be that guy lugging around a giant guitar case.

The secret to this design is the fact that I could connect the neck directly to the soundboard of the guitar without using any reinforcement pieces of material. I was able to do this by carefully considering the best materials and construction for the guitar. I knew that I wanted to use carbon fiber because it has

the highest strength properties but I wasn't sure the best way to utilize it since carbon fiber also tends to be flexible. I began considering a sandwich material but I wasn't sure what to use as my core material.

After extensive research, I knew that balsa was the perfect choice for my core material. It would offer good acoustic properties and also greatly increase the strength of my soundboard without adding weight or a large depth. I began designing around this idea and preparing how I'd approach laying it up.

The soundboard

I chose to do a layup on a metal plate for a smooth surface finish and then vacuum bagged and baked the layup. In order to have a spot to lay the guitar neck in, I had to design a simple male style mold out of wood that was the depth of the where the neck would lay. I decided to have 5 layers on each side of the balsa core. The orientation was 0- 90 – 45 - -45- 0 – core – 0 - 90 - 45- -45- 0. I did this because it has adequate support on the zero direction where the strings pull, but it also has enough support to keep the guitar from twisting. As I was laying up, I had to cut strips as well as sheets in order for the carbon fiber to take to the contour of the mold for the neck hole. I had to coat the neck hole mold in a thin plastic to allow it to remove from the carbon fiber rather than bond to it. It was also a little bit tricky to get the balsa core around the neck hole because I had to cut little balsa pieces to lay around it and then lay carbon fiber on top of that. Upon completion, I prepared it for vacuuming with all the appropriate materials and put it in the oven to bake for 7 hours. Once it finished, I saw that the layup turned out well and I was even able to remove the neck hole mold without any trouble.

The back piece

The design also required a back piece. For this piece I decided since it wouldn't be subjected to the stress the front piece would be from the strings, I could make it without a balsa core. I chose to make it from 7 layers of carbon fiber with a 45 - -45 – 0 - 90 – 0 - -45 – 45 orientation. I chose this layup because it was a nice all around resister to stress from any direction. I used the 45 as the final finish rather than the 0 I used for the front piece. It think this angled finish on the back piece looked nice and added some style to the guitar.

The collapsing mechanism attachments

Before I cured my back piece layup I also needed to add in the parts I need for the collapsing mechanism in the guitar. The mechanism was based on the idea of a camping stool turned on its side. It required wooden dowels to slide a tiny bit in order to allow the guitar to open up. I needed carbon fiber holders for the dowels but two of them need some extra space to allow the dowels to slide. It was tricky determining how much space that should be, but after prototyping a simple design out of cardboard first, I determined about a half inch of dowel slide distance would allow for the guitar to open up to a depth of around 4 to 5 inches. This was the target depth I wanted the guitar to be at, so, I designed a simple wood mold that was the height of the dowel but had that extra half inch of width. Using this mold and the dowel itself I created the two attachment pieces. I laid up two sheets of carbon fiber over it. This was a simple 0-90 orientation and doing this created the attachments used to connect the collapsing mechanism to the guitar front and back panels.

After laying up both the back panel and the attachment pieces on the metal plate I vacuum sealed it and put it in the oven to bake. The final result turned out just as I planned. There was a small amount of space between plies on the attachment pieces because the contour was so great but it didn't weaken the overall part too much.

Creating the bolt on neck

With all my carbon fiber parts cured the next step was to attach the neck to the soundboard and set the bridge of the guitar. Since this design required a quick release neck I needed to make alterations to the neck before I could attach it. The neck was designed for wood screws but I wanted it to have a metal threading inlay and be able to be bolted down. This way it could be removed quickly and often. I checked many hardwood stores and couldn't actually find what I needed. Due to this I ended up buying some bolts and custom designing metal inlays for the bolts.

Designing the metal threading that went into the neck proved to be challenging. I had to thread both the outer side and inside of a steel tube. The first time I tried the tube was aluminum and slightly too thin and it kept peeling off the whole side of the tube. I switched to machined steel due to its strength and slightly increased the thickness of the walls of the tube. The steel was so hard it was difficult to tap but eventually I got it tapped and was able to cut three pieces off it. When I cut the pieces it made small burrs on it that made it difficult to screw the bolts through the inner dimension threading. I had to gently work the bolts through each one for about an hour in order to make it so that each bolt glided through the threading.

The guitar neck was then drilled and tapped to the outer threading of the metal inlays. The metal inlays were screwed in and the bolts were able to screw into the inner threads of the inlays. I chose a three bolt design systems of attachment that is model off of an old fender neck attachment orientation. Due to a metal bar in the center of the neck, I had to reduce the hole depth of the center bolt hole. I accidentally drilled a tiny bit into the metal rod but it seems to be ok.

Attaching the neck

With the neck ready to be attached, the next trick was matching the holes in the guitar neck hole to the soundboard inlay where the neck sat. This proved to be tricky because how can you mark where a hole goes if you don't can't access it with a pen once it’s in place. In order to solve this problem, I used a thin layer of playdough and put it in the neck hole. I then matched the guitar neck where I needed it to be and pressed down on the playdough which marked the spot where I needed to drill my bolt holes. This worked well and I was able to attach the neck. Once attaching, I realized I'd need a metal plate to distribute the load of the bolts squeezing on the composite. I was able to cut a steel plate and used clamps to match the hole marking patterns and run a drill though the plate. This sounds simple but the slightest misplacement of the hole on the steel plate would make it useless because then it wouldn't match up to the guitar neck.

Attaching the bridge

I finally got my neck set and bolted down with the steel plate and then was faced with the task of attaching the bridge. I used a ruler against the neck of the guitar to center the bridge. I used references to other guitars to determine the bridge distance from the neck. Through careful measurement I was able to mark out the holes needed to put in the bridge.

As I screwed into the composite part I realize it wouldn't be strong enough alone to secure the bridge. I needed a steel back plate in which to screw into and sandwich the bridge to it with the composite soundboard in the middle. Once again, I was faced with the task of matching exact hole orientation on a steel piece. Through using clamps and carefully measuring, I was able to make a back steel plate that the bridge screws attached to. This plate also had counter bored holes in which the guitar strings would go through and rest on so that it wouldn't scrape against the composite material.

Cutting the guitar shape

Now that the neck and bridge was set I needed to cut the shape of the guitar. I used a cardboard template I created beforehand and traced it onto the both the front and back panel. I used a dremel to cut the shape of the guitar on both panels and then used sand paper to grind it down to the final dimensions. This was a messy process and took quite a while

Cutting the Pick-up holes

Due to the odd shape of the holes where the pick-ups would lay, I knew I needed a template to locate the best spot to put in the pick-ups. I used a different guitar to create a template shape and through careful measurement I traced on the two spots for the pick-up holes. I then had to use a Dremel to cut out this complicated shape with a round blade! Through using the sanding attachment I was able to get the shapes cut out and the pick-ups fit into the holes.

Cutting the sound holes

For the sound holes, I used the special cookie cutter style drill bits that create large circular holes. Since they were cutting carbon fiber, they dulled after one hole and I had difficulty cutting any more. I used a couple different sizes and was able to create the sound holes. I then used different sizes of drills to create the pattern around the sound holes.

Installing the electronics

I measured out the hole size for each the electrical components and also the slit length I needed to install the electrical switch. I drilled and cut all the necessary holes and began installing each of the electrical components. I had to drill small holes in the part because it was too hard to screw directly into the carbon fiber without first having a guide hole. Installing the switch was tricky because it required a hole that only went halfway through the part. Through just carefully feeling when the drill hit the balsa core I was able to achieve this task.

I installed the pick-ups and wired up all the electronic components. I used electrical tape to secure all the wire to the back of the soundboard. I tested everything out on an amp and it all worked the first time around!

Creating the collapsing mechanism

For the collapsing mechanism I used magnesium because it has a high strength to weight ratio and it isn't as flexible as aluminum or steel. I cut each strip to length and marked out the center of each. I then attached the wood dowels to the end of each strip and attached the strips together at the center. This creates two teeter tooter type strips that are connected to each other by the wooden dowels. The dowels near the top of the guitar were cut shorter to allow the neck to sit inside the guitar when it is collapsed.

Attaching the collapsing mechanism

To attach the mechanism I used my carbon fiber parts I designed and epoxied each attachment to the soundboard with the wooded dowel inside. Next I attached the back panel using the same method. After everything dried both panels were attached to each other and could be drawn apart or pulled together.

Designing the walls

The guitar now needed walls to be complete. I needed something flexible so that the guitar could still collapse. It also needed to resonate sound as well. The material selection proved to be hard but I eventually decided on making my own laminate material. This involved using packing tape to coat aluminum foil. Then, sewing this onto a polyurethane coated piece of polyester created my wall material.

Attaching the walls

I measured out the wall thickness on my cloth and used superglue to attach the wall. The front and the back has a spot that I left blank to allow access to the inside of the guitar. These spots have an extra piece of wall that velcros on.

Conclusion

I am happy with how my guitar turned out. I think I could make the design even better though. Rather than using cloth I think a type of Tupperware lid that fits around the outside of the two pieces of the guitar would be a better solution.

Composite Joke I wrote

Why do fiber strands get sad when they are impregnated in a thermoplastic?Because thermoplastics don't cure about them like thermosets do!!