To simplify the process of creating a CNC guitar body, we created a mold for making epoxy poured guitar stocks that combine epoxy resin with other materials like wood and other found objects. Silicone can be measured (carefully) and mixed so it can poured into a mold that we designed in Fusion 360 to be milled out of foam insulation.

After several revisions to the milled foam form, we poured the two-part silicone into our mold to create the silicone mold shown here. Considerations included the thickness of the finished silicone, the depth of desired guitar stock, and the thickness of the insulation. We ended up gluing two pieces of 2" thick insulation together so we could use more than a single 2" piece to create the mold.

One challenge was mixing the correct proportion of silicone to hardener. The instructions recommend a ratio of 10:1 based on weight (not volume). We used Fusion 360 to calculate the volume of silicone needed to fill the mold and then did some calculations including using the specific gravity of the silicone to convert that volume to a total weight of silicone in grams. The next challenge was weighing that much epoxy. The triple beam balances we have on hand could only measure about 600 grams at a time and we needed closer to 3 Kg. Furthermore, the silicone was incredibly viscous, so much of it stuck to the measuring cup each time we poured and measured around 600 grams. We developed a procedure to measure the weight of each cup to around 600 grams. Then we poured the cup into a larger mixing bucket and finally reweighed the cup to determine how much the cup and residual silicone was in the cup so we subtract that amount from the amount poured. You can check out more about our calculations here.