Week 14 — Molding and casting
Week 14 follows the official Moulding and Casting module. I used a silicone block mold (negative) taken from a 3D-printed master of a small “sprite” figure for my final project theme, then cast a rigid two-part epoxy copy. The individual assignment is the full mold-and-cast log; the group assignment summarizes our Chaihuo material and safety comparison.
Individual assignment
Off the assignment brief I focused on what I could finish at home: two AB systems (addition-cure silicone for the mold, epoxy “crystal” resin for the part), a disposable cup as a containment shell, and a printed positive I could sacrifice inside the first pour. This matches the nueval FAQ path for a negative mold, as long as the cast releases without destroying the silicone.
1) Task and design choice
My final project circles a set of three spirit-like characters. For Week 14 I wanted one tangible resin replica, both as practice and as a physical prop. I downloaded a suitable sprite-like mesh from a community 3D-printing platform, printed it in PLA as the master, and planned a single-volume pour of printed positive inside a plastic cup. Cutting the cured block open for a parting line beat designing a two-part printed mold with the time and silicone I had at home.
2) Learning (from datasheets, the group page, and trial)
Before mixing anything I read the bottle labels and supplier notes for mix ratios, pot life, and cure time, and I kept the same mindset as in our group assignment: ventilation, gloves, and not rushing the stir. The group comparison already stressed that viscosity and cure profile change bubble behavior; my own extra question was whether uncured silicone would attack the PLA master—I ran a small contact check before committing the full pour (photo below).
3) Plan
- Print master → mount / center in cup → Vaseline as release on the PLA only.
- Weigh silicone A/B, mix, pour, cure (~one day at room temperature).
- Cut a parting path, drill vent ports, demold and clean the cavity.
- Weigh epoxy A/B at the manufacturer ratio, mix until uniform, pour, cure (several days).
- Open silicone and photograph the epoxy cast (“hero shot”).
4) Process log (with photos)
5) Problems, fixes, and how this links to the group write-up
The epoxy photos document the biggest near-miss: under-mixing looks innocent but causes soft spots or sticky regions after cure. I restarted the stir until the streaks disappeared, then accepted some entrained bubbles rather than whipping air in blindly. Same lesson as the group AB-glue notes: weigh, mix until streak-free, then pour. On silicone, the curved parting cut took a while but kept the two halves aligned when I opened the block.
Compared to the official reminder about smooth mold walls without FDM toolpaths, my mold is silicone (no layer lines), but the cast surface still echoes the FDM master. Next iteration I would sand/fill the PLA or switch the master to a finer process before molding if I need a toy-like finish.
6) Files and checklist (nueval alignment)
- Design file: the printable mesh came from the community platform I used for the master; I can zip the exact STL/3MF here once I mirror it into the repo for permalinking.
- Hero imagery: silicone cavity shots + final epoxy figure (above).
- Group link & reflection: aligned with Chaihuo Week 14 group page on materials and PPE.
- MSDS/TDS: key ratios, cure windows, and ventilation notes are logged from the product sheets that shipped with the four bottles; I will attach PDF links when I mirror them next to the design files.
Group assignment
Guangzhou (Chaihuo) — group documentation: comparing molding and casting materials, safety practices, and process workflows.
Chaihuo’s Week 14 group page compares silicone brands, PPE habits, and AB epoxy mixing. I pulled their photos below (shared lab material, not shots from my kitchen bench) and wrote down what I actually changed after reading the same notes before my solo pour.
1) Silicone comparison: pick by pour behavior, not sticker price
HongDa vs ShinBon differed in viscosity and cure speed enough that bubble traps and demold effort changed on the same cup geometry. We agreed on a small test slug before any “hero” mold; the cheaper bottle was not cheaper once I counted rework on a detailed sprite shape.
2) Safety practice: gloves and ventilation before the scale
The group “bad habits” slide is blunt on purpose: skin contact and poor airflow with addition-cure silicone or AB resin is not a last-minute fix. We listed PPE, vent location, and waste cup placement in the same checklist as mix ratio so nobody treats safety as optional when the pour is already mixed.
3) AB glue casting: ratio and stir time dominate the result
Sticky or soft patches showed up when ratio drifted or mixing stopped while streaks remained. That matches what I saw on my epoxy pour (see individual section): brand name mattered less than weighing both parts and folding until the flecks disappeared.
4) What I kept for later weeks
Before mixing I now write down geometry (flex vs rigid), target finish, and the failure I expect first (bubbles, soft cure, stuck master). That checklist came straight from the group comparison and saved me from skipping the PLA/silicone spot test on my own mold.
- Pilot cast on scrap geometry before the real master.
- Pick silicone by viscosity/cure for the shape, not catalog price alone.
- PPE + ventilation on the same checklist as A:B weights.
- Log grams, ambient temp, and cure time for the next pour.
Source
Group template and media source: Week 14 — Group Assignment: Molding and Casting.