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February 2018 Update - Manufacturing the String Assembly / Speaker Box

Hi everyone,

The past few weeks we’ve been working on a number of different fronts for manufacturing the various components of the guitar: the plastics, the metal parts (including the strings, and parts to reinforce where the guitar strap buttons and input ports), light pipes, rubber parts, electronics.

This update will focus on our efforts to use urethane casting as a manufacturing technique for making high-quality plastic parts for the guitar. This update will also feature a LOT of photos.

First, we’ve been working to make the single most complex / difficult / high-risk part of the guitar - the string assembly / speaker box. This part performs two critical functions: 1) it holds the six strings for strumming, and 2) it holds the speaker in an air-tight cavity, which maximizes the speaker’s projection and volume. This part has numerous intricate features with thin walls, which increases the likelihood of trapped air pockets in the silicone mold, leading to voids in the part once it’s cast with polyurethane resin, cured, and de-molded from the silicone mold.

First, we made a two-part silicone mold from the master part. This involved putting the part in clay, and then pouring silicone to make half of the mold:

We mixed up some liquid silicone (to make the silicone mold):


We poured the mixed silicone into the mold box:

After the part was fully covered by the liquid silicone, we put the entire box in a vacuum chamber (a stainless steel vessel with a lid) to pull out any trapped air bubbles in the silicone.

We let the silicone cure, and removed the mold from the box:

We then removed the master part from the mold, and now have a high-quality silicone mold of the part:

Now that the mold was complete, it was time to cast the part.

We placed the two halves of the mold together, and secured them using flat plates:

We mixed liquid polyurethane resin with a catalyst:

Once this mixture was complete, we injected the liquid polyurethane resin into the mold, until it overflowed, so we knew all the cavities in the mold were filled with resin:


We let the polyurethane cure, and then we pulled the mold halves apart to examine our first casting.

 This first casting had a couple of major problems. First, the mold had bulged slightly open from the pressure of the injected liquid. This made parts of the string assembly too thick. Of particular concern was that the fins that hold the piezos for each string had all filled into to become one undifferentiated part:

On the bottom side of the part, a number of the screw bosses did not fill in properly, as air bubbles in the mold were not fully displaced by the liquid polyurethane:

To address these problems, we found thicker flat plates to bookend the mold halves, which should help keep the mold clamped together. We also made additional modifications to the mold by cutting little channels between the fins to ensure that the polyurethane would flow between them. We then attempted our second casting a week later:

 This time, the part was significantly improved. The mold halves had stayed together due to the thicker flat plates, so the part didn’t become too thick, and the fins for the strings were properly differentiated. 

Comparing the two parts side by side - the left part is the first casting, the right part is the second casting - you can see the spaces between the tabs that hold the strings:


 Also, the screw bosses on the back side are now all formed properly:

However, there was still one key section that still didn’t fully form properly - the part the holds the rubber parts that helps dampen the vibrations of the guitar strings and gives them a nice feel when strumming. This section had some voids due to trapped air bubbles:

To address these remaining issues, we made some additional modifications to the mold:

A week later, we tried another casting, and the problematic section is now properly formed.

Here is a photo of the three generations of parts side by side. (The part on the left is the first casting, the part in the middle is the second casting, and the part on the right is the third casting):

Given how well this third casting came out - we’re now confident that it’s possible for us to manufacture the most difficult and complex parts of the guitar using urethane casting. This third attempt at casting the string assembly and speaker box has yielded a high-quality part - one that can be used in a production unit.

Over the next few weeks, we’ll be making molds and casting the largest parts of the guitar - the guitar body front and back, and the neck front and back.

So what does this mean in terms of when we’ll manufacture and ship your guitar? At the moment, we're still thinking we’ll be able to start shipping units in Summer 2018.

Many of you have been asking for a more specific timeline one when we’ll fulfill your orders and when you’ll receive your guitars. Before we can answer that question with a greater degree of certainty, we still need to figure out how to best scale up production - how many production lines / sets of molds we can have working in parallel, how big of a facility we’ll have to rent, how many workers we’ll have to hire and train to cast the parts. And that also partly depends on how much capital we can raise over the next few months.

More on this in future updates.

Thanks to everyone for your continued support. As always, please let us know if you have any questions, concerns or comments.

Brian Fan
CEO, Magic Instruments




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