gabriel stacey-chartrand
gabriel stacey-chartrand
I originally wanted to try slip casting an enclosure for a product. The first problem to solve would have been figuring out how to slip cast holes into the enclosure (for ports, buttons, lights, silicone feet, etc.). From my research, this might work with wax, with mesas and wiping off slip when wet, or with drain plugs that are removed when the slip is wet. Could also use "fettling" by cutting out the holes during the leather stage, or by placing the holes at the top where I'm pouring the slip.
Some slip casting notes from research:
I came to the conclusion that I wouldn't have time for slip casting.
Decided to pursue casting in a two-part silicone mold instead.
Two-part silicone mold notes from research:
Candle holder / ashtray combo with silicone feet. I wanted this object to be multi-use. I also wanted to play with the light of a tealight in the center, using the bowl of the ashtray as a sort of reflector and the teeth as ways to cast interesting shadows.
Created a design that would be easy to cast in a two-part mold. Made sure to design draft angles on all surfaces. Realized too late that there were two surfaces I forgot to add draft angles to.
I redesigned the main (outer) cavity to be shallower. I also wanted the tealight candle portion to sit lower to create more interesting effects with the light reflection and shadows.
Ball shaped silicone feet would require a two-part mold, which is overkill for this part. I decided to redesign them as cylinders to use a one-part milled wax mold.
Initially I wanted to cast it out of pewter using Mold Max 60 or another heat resistant silicone. It was recommended to me that I start by casting with something that isn't metal, and due to the time constraint I wouldn't have time to also cast out of metal. Pewter was also hard to find locally and was very expensive.
I first considered using plaster, but the object wouldn't be functional as intended and would end up being purely decorative. That ruled out plaster for my design.
I then explored cement or cement-like options. I considered Portland cement and Portland cement mixed with sand. Due to the time constraints, I looked into fast-setting cement mixes, but the local options were limited and wouldn't give me the low viscosity needed to fill my two-part mold.
That led me to Jesmonite, a water-based acrylic resin that gives a stone/concrete-like finish, demolds in under 2 hours, and is much more controllable than bagged Portland cement for a tight timeline. Picked it up from FormX in Poble Nou (C/ Pujades 147), which is a Smooth-On distributor that also stocks Jesmonite and silicones. Resineco / Jesmonite Store in Montmeló is the more specialized option but was too far for my two-day window.
It addressed both of the issues that ruled out the others: it's water-based (so non-combustible, important for a candle holder), and it's specifically designed to be poured into molds rather than brushed or laminated. The stone finish also fits the aesthetic I wanted, and the under-2-hour demold time made it workable within the two days I had left.
To prepare the first print for creating a silicone mold, I went through a few steps:
Important technical specifications:
Ran into a serious problem with XTC-3D that ruined my print. The mix ratio was correct (100A:42B by weight), but the mix went exothermic in the cup and got super hot within a few minutes, hardening almost immediately and ruining the print underneath. The pot life is 10 min in mass vs. 15 min on a flat tray for a reason: leaving the mix concentrated in a cup lets the heat build up and trigger a runaway cure. Lesson learned, pour it onto a flat tray or palette right after mixing so the mass spreads thin, and work quickly.
Since I had to reprint the master model, I reworked the file to add draft angles to the two surfaces I had forgotten about.
First iteration had silicone feet on one half of the wax block and small domes to act as registration keys for the two-part silicone mold.
Modela kept crashing when I tried to export the file with both the registration keys and the silicone feet. Eventually we figured out that if the model was split in two, Modela didn't crash. For some reason it didn't like the two geometries together.
Ended up 3D printing the registration keys instead. Two types: pyramids and domes.
Remade the model file with only the silicone feet filling the whole block.
Tried to figure out the dye/pigment to use for intrinsic colouring, but didn't have suitable dyes on hand in the lab.
Poured a test run of clear silicone with no dye.
Type of silicone used: Feroca EASYPLAT MOLD-40.
Important technical specifications:
Amount used: 31g of each part. Mixed vigorously, then placed in the vacuum chamber to remove bubbles.
Noticed a problem area for bubble formation in the pin area at the bottom.
Accidentally melted a hole through the base using the Dremel wire brush to try to clean it more quickly.
Looked into options for filling the hole. Bondo (polyester body filler) was the ideal pick, fastest cure (5–15 min), very sandable, and a known-safe option with silicone mold making. Couldn't find Bondo locally, so I picked up a generic multi-use two-part epoxy putty instead.
The result was not great. The curing time is only 3 minutes and it's very difficult to fill the spaces smoothly. It hardened before I could finish getting the result I wanted.
To be continued...