Week 14 - Molding and casting

Group assignment for this week is on the Chaihuo Week 14 group assignment page. The rest of this page is my individual work.

Individual assignment

I cast a small Brainfog nameplate for my final project. The workflow is a two-step mold: 3D-print a rigid master, pour silicone inside it to get a flexible negative, then pour clear epoxy resin into that silicone to get the finished part.

Assessment item	Where it is covered
Design a mold around your process and cast parts	CadQuery master design, 3D-printed cup master, silicone negative, resin cast.
Smooth surface finish without visible toolpath	0.2 mm layer height on the logo face; silicone hides most print texture on the cast face.
Document mold design and machine settings	Design workflow, Bambu Studio settings table, step photos below.
Safe mold making and casting	Scale weighing, gloves, ventilation, release agent, bubble removal with tweezers.
Problems and fixes	Problems table at the end of this section.
Design files and hero shot	STL download; demold photo with master, silicone, and cast together.

What I wanted to make

The part is a 48 mm circular badge with raised "Brainfog" text. I tied it to the final project branding instead of making a random test shape. The geometry is simple on purpose: one open cup, no side undercuts, so the silicone pad can peel out without a multi-piece mold.

Master design

I modeled the master in CadQuery: a flat block with a recessed circular basin and mirrored text cut into the floor. The text is mirrored on X so the silicone copy, and later the resin copy, read forward. I exported brainfog.stl and sliced it in Bambu Studio on the lab X1C.

Brainfog master model in Bambu Studio — CadQuery export opened in Bambu Studio before slicing.

Setting	Value
Printer	Bambu Lab X1C
Plate	Textured PEI
Profile	0.20 mm Standard @BBL X1C
Material	PLA
Nozzle	0.4 mm

3D printed Brainfog master on the build plate — Printed master straight off the plate. Layer lines show on the outer wall; the logo floor is the surface that matters for molding.

Silicone negative mold

I used food-grade addition silicone (Shore 20, parts A and B). The label calls for a 1:1 weight ratio. I weighed both parts on a digital scale, mixed in one direction with a wooden stick, and kept the working time short once A and B touched.

Material	Mix ratio (by weight)	Notes
Silicone A + B	1 : 1	Match weights on the scale; do not guess by volume.

Silicone A and B bottles and scale — Silicone A/B, scale, and release agent ready on the bench.

Applying Vaseline release agent to the printed master — Vaseline brushed on the printed master so cured silicone releases cleanly.

Weighing silicone part A — Weighing part A before adding part B.

Weighing silicone part B to match part A — Part B weighed to match part A at 1:1.

Stirring mixed silicone — Stirring until the colour and texture look uniform.

Pouring silicone into the 3D printed master — Pouring mixed silicone into the printed cup master.

Cured silicone in the master mold with bubbles being removed — After cure: picking surface bubbles with tweezers before demolding.

Silicone negative mold next to the printed master — Hero shot: flexible silicone negative beside the rigid PLA master. The text reads mirrored in the rubber, which is what I expect from a negative.

Resin cast

For the final part I used two-part crystal epoxy (hard glue A/B). The bottle label specifies 3:1 by weight (A : B). I poured 120 g of A and 40 g of B in one run so the ratio stayed exact, stirred until the streaks disappeared, then poured slowly into the silicone mold.

Material	Mix ratio (by weight)	Example batch
Epoxy A : B	3 : 1	120 g A + 40 g B

Epoxy resin A and B bottles and scale — Epoxy A/B and scale. Label shows 3:1 weight ratio and 2.5:1 volume ratio; I used weight.

Weighing 120 grams of epoxy part A — Part A: 120.0 g on the scale.

Weighing 40 grams of epoxy part B — Part B: 40.0 g added for a 3:1 batch.

Stirring mixed epoxy resin — Mixing until the swirl marks are gone.

Pouring resin into the silicone mold — Pouring into the silicone negative. Tweezers again for surface bubbles.

Cured clear resin cast in the silicone mold — Cured clear cast still in the silicone mold. "Brainfog" reads correctly on the part.

Demolded resin cast

After the epoxy fully cured, I peeled the flexible silicone negative off the part. The text came out readable on the resin disc, and the silicone mold stayed intact for another pour if I need one.

Clear resin Brainfog disc beside the silicone mold after demolding — Fresh demold: clear resin disc beside the silicone negative. The mold still shows reversed lettering inside.

Finished clear resin Brainfog badge top view — Finished cast on the bench. Raised "Brainfog" text reads forward after demolding.

What I learned from group work

The group silicone comparison (HongDa vs ShinBon) and the AB-resin safety review changed how I ran my individual pour. I weighed both silicone and resin instead of guessing, kept gloves on for the whole mix-and-pour window, and did a small test mindset even on a single badge: check ratio, mix time, then pour. Viscosity differences between silicone brands would have changed bubble retention; I picked the food-grade A/B pair we had tested in group and stuck to the labelled ratios.

Problems and fixes

Problem	What I did
Small bubbles on the silicone surface after pour	Waited until the mix was slightly thicker, then popped bubbles with tweezers before full cure.
Layer lines on the PLA cup wall	Accepted on the non-cosmetic outer wall; the logo floor is the mating surface and copied cleanly into silicone.
Silicone sticking to PLA	Brushed Vaseline on the master before the first pour.
Resin bubbles in the final cast	Slow pour, same tweezers pass on the surface, full 3:1 weight mix before pouring.

Design files

Download brainfog.stl