We’ve built a cardboard box around the clay that will enclose the liquid silicone and enable it to cure (harden).
Next, we mix the two parts of the silicone (the silicone and the catalyst) and start pouring the liquid silicone into the box:
We then put the silicone under vacuum to draw out any trapped or suspended air bubbles. We let the silicone cure for around 48 hours, remove the cardboard box, and turn it upside down to extract the front body from the clay:
We then rebuilt the box and poured liquid silicone on top of the front face to form the top half of the mold:
After degassing the mold in the vacuum chamber and waiting another 48 hours for the second half of the mold to cure, we got our chance to see whether the mold had formed properly. We separated the two halves of the mold:
And a big sigh of relief, the mold formed well. The front face of the guitar front body looks smooth, with no air bubbles or voids in the silicone:
Here it is again, along with the master part:
We demolded the master part to examine the bottom half of the mold:
and… voila, the bottom half of the mold also looks good!
All the ribs and screw bosses looked to have formed nicely.
Here is another look at both halves of the front body mold:
OK, let’s try to cast some guitar bodies!
First, we had to create end plates for the mold so we could keep the two halves pressed together, to avoid any bulging from the polyurethane resin as it is injected into the mold:
We mixed up the polyurethane resin and the catalyst:
We injected the polyurethane into the mold and put it under vacuum to evacuate the air bubbles:
We waited for the resin to cure, and we opened the mold:
And then we demolded the part fully:
And the first thing we did was turn the part over to check whether the internal features had formed properly:
All the structural ribs and screw bosses formed properly and accurately. There were a couple of tiny voids, nothing that we are concerned about.
However, some of the curves of the body didn’t fill in properly, especially around the bridge. The mute bar also had a major missing void.
You can see the unfilled areas when we hold the part up in the sunlight:
Over the next few days, we modified the mold by cutting small channels to enable the polyurethane to flow more easily to the affected areas.
And we tried casting the part again:
The second attempt at the part was a definite improvement over the first attempt. Although some voids are still present, they are much smaller:
The interior looks pretty good:
But, still not at the level of quality that we’d like for this part.
So, back to improving the mold and casting the part a third time:
The voids around the bridge and mute bar are yet even smaller:
So this is where we are currently. I think one or two more attempts at modifying the mold and casting this part should get us to the right quality level.
If that doesn’t work, we always have the option of putting this mold into a pressure pot to pressurize all the trapped air bubbles away, although that would require a capital investment of around $20,000 in a large pressure vessel and an industrial air compressor. We’re trying our best to not have to incur that expense.
After the front body comes the back body, then the neck (front and back). (All the remaining parts after these are small and nowhere as challenging as the guitar body.)
Overall, we’re continuing to make steady progress. We wish we were going faster, of course, but with limited resources we’re doing our best.
Regarding schedule, we’re still on track for initial shipments this summer, although it’s looking increasingly like late summer. We’re continuing our efforts to raise funding, and if we’re successful, we’ll be able to accelerate with additional resources. (We’re currently applying to a couple of programs that provide funding to hardware startups manufacturing in Southern California. We’ll let you know if we have good news on that front.)
Thanks again for your continued patience and support! As always, we welcome your comments, questions, concerns and criticism.
Best wishes to everyone for a good Easter, Passover and Spring!