I hope you had a wonderful holiday with your friends and family!
We’ve heard from many of you that you’d like more frequent updates, so we’ve made it our New Year’s resolution to provide that. We’re targeting two updates per month. (We’re not sure if this is the right frequency, and we’re also not sure what level of detail makes sense, but let’s give it a try and see how it goes.)
Since our last update on December 22, 2017, we’ve been gearing up to start making start making guitar parts using urethane casting.
A quick primer: urethane casting is done by pouring liquid polyurethane resin at low pressure, at room temperature, into soft silicone molds. This is a low-capital way to make high-quality plastic parts. (We had previously planned to use injection molding, which is done by shooting/injecting molten thermoplastic at high pressure into a hard steel mold.)
Both are well-established techniques for manufacturing plastic parts. We designed and engineered the parts of our guitar to be injection molded. Injection molding likes plastic parts with thin walls (less than 4mm), as the heating and cooling of the plastic resin can cause uneven shrinkage, discoloration, and other deformations in the part.
However, urethane casting prefers thicker walls - because thin walls in the mold has the potential to trap air bubbles, which can cause parts to come out with voids, as the liquid polyurethane resin solidifies and hardens around the air bubble. (The polyurethane resin is poured, not injected at high pressure, so air bubbles aren’t forcibly displaced.)
We’ve worked with James, our master mold maker (pictured below), to analyze every plastic part in the guitar, identify the challenges in casting each part, and develop a plan for the difficult parts.
There are two parts in the Magic Instruments Guitar that are particularly challenging for us to make with urethane casting: 1) the string assembly/speaker box and 2) the back of the guitar body. Both of these parts / pieces have intricate details with thin walls.
Last week, we started the process for making the mold for the most difficult part - the string assembly/speaker box. This is an internal part that does double duty: 1) it holds and supports the 6 strings and the 6 piezo sensors for each string, and 2) it holds the guitar speaker and creates an airtight chamber within the guitar to maximize the speaker’s sound projection and sound quality.
We’re making a two-part mold, with a top half and a bottom half (similar to an injection molding tool), as the parts we’re making aren’t flat on either side.
The mold-making first starts with taking the “master" part and first blocking off areas, with clay, that we don’t want to cast in the first half of the mold. Our master part is the production-quality part we had CNC machined to our final mechanical design last year by one of the world’s leading model shops. It has the exact dimensions, color and finish that we want to see in the final product. We’re using sulfur-free clay to holds the master part in place, so it won't affect or change the finish on the part.
In this photo, you can see the string assembly/speaker box part sitting in the clay, as we prepare to make the top half of the silicone mold.
James is working on placing the “part line” - the place where the top mold and the bottom mold come together. On this part, which is a fully internal part, the cosmetic appearance of the part line isn’t as important as external-facing parts. However, for ease of demolding the part, where the top and bottom halves of the mold come together is important.
We’ll be putting the string assembly/speaker box and the clay base inside a wooden box, and then pouring a platinum silicone on top of this to create the top half of the mold first.
After we create the top mold, we’ll do the same steps to create the bottom half of the mold.
To reduce air bubbles, we’ll be casting the polyurethane resin under vacuum. We’ll place the silicone molds in a vacuum vessel, pour the polyurethane resin into the molds, and then place a clear polycarbonate top and turn on a vacuum pump to evacuate the air inside the vessel. We hope this will enable us to reduce / minimize the air bubbles in the molds, because (in theory) all the air within the vacuum pot should be evacuated, leaving only the polyurethane resin inside the silicone mold.
We’ve located a vacuum vessel large enough for the guitar body (yes, it looks just like a huge, shallow pot):
We’re making the molds for other (small) parts at the same time.
We’ll be pouring silicone over the next week or two to create the first set of molds. Sometimes, it takes a couple of tries before we get it right, so wish us luck that the molds come out well!
We’ve also been hard at work on finalizing the electronics for manufacturing, firmware, upgrading our email infrastructure, and sorting out shipping and payments for international reservations/ orders. We’ll have more on those subjects in future updates.
Thanks everyone for your continued support and patience! We look forward to getting your comments and questions.
CEO, Magic Instruments