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Friday, 10 February 2012 13:10

Protecting Your Guitar from Wear

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This article covers my concept and design process for creating a sound-hole guard for my acoustic guitar. The idea was to protect my guitar from damage and wear after long and repeated use of a pick while strumming.

Some time ago I decided to replace the pick guard on my vintage Guild acoustic guitar. I play it all the time, and it holds a lot of sentimental value for me. It was my very first guitar. I purchased it new back in 1982 in Northern California. After nearly 30 years of use, some minor maintenance and repairs were in order, including replacing the original pick guard. I removed the old pick guard, cut out a new pattern matching the old guard (using new acrylic plastic) and applied the new one on to my guitar. That’s when I decided something needed to be done in order to prevent any further damage to the lower portion of the sound-hole. I noticed over many years using a pick while that this area had eroded away considerably. Bare wood from the soundboard was now exposed and continuing to grow in length downward from the sound-hole edges. Depending on the guitar manufacturer, there is usually a gap between the edge of the sound-hole and the beginning of the pick guard, which runs concentric to the sound hole. Regardless, the edge of the sound-hole and soundboard on acoustic guitars are exposed and unprotected from damage, something where even moderate use can have long-term affects.

My initial concept was to develop a flat pattern that could be laid onto the soundboard with an overlapping piece that bent around to the back of the sound-hole. The development piece would have to have a pressure sensitive adhesive in order to adhere in place. I used a .020 thick piece of Mylar for the original pattern, but soon afterward came up with another concept that would act as a more permanent and stronger solution. That fix turned out amazingly well and is still on my guitar.

I designed a flat pattern out of .125 thick piece of polycarbonate, heat formed it around a fixture that duplicated the sound-hole/soundboard dimensions. This design acts as a clip that fits over the lower half of the sound-hole. I attached the prototype piece onto my guitar with some silicon rubber adhesive in order for it to stay in place. Although this prototype proved to prevent any further damage to the area, I felt I needed to refine the design by reducing the wall thickness (the prototype appeared to be too bulky) and to simplify the fit by eliminating the use of an adhesive.

Then I picked up a seat of SolidWorks so I could properly build and design 3D solid models. This was something I had been putting off and had wanted to do for quite a while. My guitar project prompted me to take some action. After familiarizing myself with the software, I decided to tackle the sound-hole guard project. My first design incorporated negative draft on the two walls to act as a clip to squeeze onto the soundboard. I also designed three concentric ridge features on the inner wall to act as teeth to bite onto the soundboard, preventing movement and eliminating the need for the adhesive.

After converting to my first .stl file, I was ready to shop for a prototype service that would build the part. I was a little disappointed in discovering the pricing structures I was looking at, as my part did not seem very intricate or big. Searching further, I found ZoomRP who’s pricing seemed reasonable. Plus they offered very fast turn-around times, and their on-line quoting system was convenient and almost immediate, within seconds after submitting the .stl file. I decided to go with the Poly Jet HD Blue process, which advertised the highest resolution, highest accuracy, and was specific to smaller prototypes.

When I received my first part, I was completely impressed by the accuracy and quality of the surface finish and to the details of the very small teeth on the inner wall. My part would allow me to test for fit and function on my guitar. The only problem I experienced was an interference issue, which I overlooked in the design process. The inside edge of the outer wall of the part was catching on the edge of the pick guard. This prevented it to seat properly. The dimension of the outer wall of the part was too close to the location of the edge of the pick guard. So I went back to solving this issue on SolidWorks.

I also felt it necessary to play around with wall thickness and draft. Thickness of .100 still seemed too thick and the fit also seemed too tight on the guitar. I did extend the front wall to fit over the pick guard and added a small radius extending the entire inner edge.

A couple of designs later I was finally able to fine tune all design concerns including the right amount of draft, wall thickness, overall length, and front wall length, (final part: pic-4, front view and back view). I now feel very comfortable that this piece will fit and offer protection on all acoustic guitars that have round sound-holes.

I now have a provisional patent, and plan to go forward with obtaining a final patent. I am sure my sound-hole guard product will catch on and appeal to all levels of musicians who can appreciate the need to protect their investment, whether sentimental or financial.

For information, visit: www.Strumhard.com or www.ZoomRP.com

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