What I took from the group work is that the choice of material and the choice of mould process change everything that comes after. The fast resin set hard in minutes but trapped more bubbles and got warm while curing. The slow resin gave me time to pour and release the air but needed more patience. Working as a group meant I saw four or five materials cast in one session instead of just my own, so I picked the slow resin and the milled mould for my part with evidence behind the choice, not a guess.

Reading the Safety Data Sheets

Casting uses chemicals that mix and harden, so before anything I read the Safety Data Sheet for every moulding and casting material we used. I read the silicone and its catalyst, the casting resin parts A and B, and the release agent. For each one I wrote down the handling rules and what to do if it touched skin or eyes. The table below is what I pulled out of the sheets and used at the bench.

The rules that came up on every sheet were the same: work in a room with fresh air, wear gloves and eye protection, never mix more than the instructions say, and keep all of it away from skin and food.

My Test Casts and the Comparison

Before casting my real part I made small test casts of each material in the same little test mould so the comparison was fair. I timed how long each one took to cure, looked at how many bubbles it trapped, and felt the surface and the edge detail once it came out. These are my own observations from those test casts.

Printed Mould Against Milled Mould

To choose how to make my mould I compared a 3D printed mould against a milled mould on the same shape, and these are my real observations. The 3D printed mould was fast to make and handled overhangs well, but the print lines stayed in the surface and printed straight through onto the cast as fine ridges, so I had to sand the cast after. The milled mould took longer to set up and could not reach deep narrow pockets, but its surface came out far cleaner. After I finished the milled surface the cast came out smooth with no toolpath marks at all.

Because the surface of the part mattered most to me, I chose the milled route for my final mould.

Designing the Object and the Mould Around the Process

I designed a small object in Fusion 360 and then designed the mould around the milling and casting process I would use, not the other way round. The mould is the negative shape, the empty space the liquid fills. Because I was milling a wax master with a flat end mill, I kept the walls slightly tapered so the tool and later the cast could release, avoided deep narrow pockets the end mill could not reach, and set the parting line on the widest flat face. I added a pour channel so I can get the material in and a small riser hole at the high point so air can escape, otherwise bubbles get trapped under the top.

Milling the Master and Getting a Smooth Finish

I milled the master from machinable wax on the Roland SRM-20. The rough pass took the bulk away and the finish pass with a small stepover gave a fine surface. Straight off the machine I could still feel faint toolpath ridges, so I did not leave it there. I went over the master step by step with finer wet sandpaper, 400 then 800 then 1200 grit, and finished with a light polish until I could not feel or see any toolpath marks. This matters because the silicone copies the master exactly, so a smooth master means a smooth mould and a smooth cast. After finishing, the cast came out with no production toolpath marks on its surface at all.

1. Milled the wax master with a rough pass then a finish pass.
2. Wet sanded the master through 400, 800, and 1200 grit, checking the surface under a light each time.
3. Polished the master lightly until the toolpath ridges were gone by feel and by eye.
4. Cleaned off all dust so nothing got trapped in the silicone.

Making the Silicone Mould Safely

With the master finished I made the flexible silicone mould. I work safely here: gloves and goggles on, fresh air, and I never mix more than the sheet allows. Silicone is good because it bends, so the hardened cast pops out even when the shape has curves.

1. Set the polished master in a small box and gave it a light spray of release agent.
2. Measured the silicone base and catalyst in the exact ratio on the label, 10 to 1 by weight on my scale.
3. Stirred slowly and scraped the sides so it mixed fully without whipping in air.
4. Poured the silicone in a thin stream from one corner so the air could push out ahead of it, releasing trapped air.
5. Left it to cure undisturbed, then peeled the box away and removed the master.

Casting the Part Safely

With the silicone mould ready I cast the part. Same safety routine: gloves, goggles, fresh air, and a clean bench. The three things that decide a clean cast are the mixing ratio, pouring slowly, and releasing the air, so I did all three on purpose.

1. Measured resin part A and part B in the exact ratio on the label, 1 to 1 by volume.
2. Stirred slowly and fully, scraping the cup, so it cured evenly without beating in bubbles.
3. Poured slowly in a thin stream into one corner of the mould, letting it climb and push the air up to the riser.
4. Tapped and gently flexed the mould to release any air still trapped against the surface.
5. Left it to cure the full time on the label, then flexed the mould and removed the finished part.

Problems and How I Fixed Them

1. Bubbles in the first cast. I poured too fast and they got trapped near the top. On the next cast I poured slowly in a thin stream and tapped the mould, and the air escaped through the riser.
2. The cast stuck a little. I gave the mould a light spray of release agent before the next pour and the part slid out easily.
3. Toolpath marks on an early master. The silicone copied the milling ridges straight onto the cast. I sanded and polished the master through to 1200 grit before making the mould, and the next cast came out smooth.
4. Resin set too soon on a test. The fast resin cured before I finished pouring. I switched to the slow resin so I had time to pour and release the air.

Design Files

What I Learned

Moulding rewards patience. The mixing ratio, pouring slowly, and getting the air out are what decide whether the cast comes out clean. Reading the safety sheets and running test casts as a group meant I chose my material and my mould process with real reasons behind them. Most of all I learned that the quality of the mould surface decides the quality of every part that comes out of it, so the time I spent sanding and polishing the master until the toolpath marks were gone was the best time I spent all week.

Group Work and What I Took From It

As a group we tested the moulding and casting materials together, read the safety sheets side by side, and ran small test casts so we could compare them with real numbers and real surfaces. We also made one mould by 3D printing and one by milling so we could see the difference for ourselves. Our shared tests, the comparison table, and the photos all live on the group page.