Foundry - Polygons in Bronze: Part 4
I realized that I needed some sort of lip so that I could let the silicone mold wrap around the bottom of the cat for an attempt at a hollow wax shell.
I kept struggling with deformation along the flat base. I was successfully able to mitigate this by adding a thin wall along the outside edges of the entire base and printing "flat" on the buildplate.
I also increased the height of the lower wall for mold-making purposes.
The final print - I used a resin that had anecdotal success with silicone molding. (Apparently a sulfurous chemical in most UV resins inhibits the curing of Platinum-Cure silicone.)
Drain holes filled with sulfur-free clay.
Rebound 25, a platinum-cure silicone from Smooth-On. (Yes, I made this mold in my shower...)
The finished and trimmed silicone mold jacket.
Apparently some of these 3D printer manufacturers make in-chamber heaters... I bought one and it works amazingly well. It is small, about 2x2x4" and fits right in the back of the 3D printer's acrylic chamber. It has a built-in thermometer that makes sure to keep the temperature right around 25C.
After one print with this heater, I knew it was the perfect solution. The print was free of layer shifts and all other temp-related issues. However, it still had some soft/rounded corners caused by a lack of supports along the flat plane that makes up the base of the sculpture. To fix this, I just added a super thin wall along the outer edge of the base. I also added a wall that lifts the cat into the air so that I can make my silicone mold wrap around the bottom and facilitate the making of a hollow mold for wax casting.
The light grey resin that I was using previously, like most UV printing resins, has some polymers in it that will inhibit the curing of platinum cure silicone. The darker navy-grey resin has had anecdotal reports online of being less likely to cause cure inhibition as long as one uses high-quality silicone, such as the Rebound 25 that I am using for this project.
Silicone types: the two main silicones used for mold-making are tin-cure and platinum-cure. Platinum cure silicone is usually a bit more expensive by volume, and is more temperamental when it comes to cure-inhibition. However, it is more flexible, has less shrinkage, and is less prone to developing air-bubbles when not using a pressure pot to degass the silicone (a small chamber that uses a vacuum to suck the air out of silicone to remove air pockets and bubbles introduced by mixing the two parts that cure into stable silicone). By using platinum-cure silicone, I can have a thin silicone mold that saves me money at the cost of time. Rather than pouring a block of silicone around my sculpture, I used a method known as brush-up mold making. With this method, I mixed individual layers of silicone and brushed them onto the master layer-by-layer allowing them to partially cure between layers. To create the entire mold, it took me the better part of a day.
Once the silicone mold was completed and cured, I trimmed the edges and many sharp peaks and waves along the surface. Then, I created a "mother mold" or "mold shell" (same thing, used interchangeably) out of plaster bandages and thickened it up with plaster of paris. The plaster took much too long to harden and dry. It also crumbled all over. This led to my first wax cast being a bit of a disaster...
