Thread by @GregDavill

Time to cast some polyurethane resin parts! (Thread)

These could probably be made with a 3d printer.. but that's a lazy way. 😅

The blue silicone molds were created ages ago from these ren-shape masters

Renshape is free machining plastic (maybe polyurethane?). Easy to machine, and captures alot of detail. I carved these out on my cheap desktop milling machine.

Unfortunately I broke these during release.

The silicone I used for the molds is this QM262 blend, it's very low shrinkage high shore hardness Platinum cure silicone. It's a silicone recommended in this guide, which I highly recommend reading through: lcamtuf.coredump.cx/gcnc/

I still have this polyurethane resin. It's now a few years old, so we'll see how it performs...

J-wax is a spray on waxy release agent that you can spray on the silicone to prolong it's usable life.

Polyurethane Part-A is typically reactive to air, so and liquid that spills under the cap during pouring ends up hardening and sealing the entire bottle shut.

vice-grips to the rescue!

Degassing trapped air bubbles from mixing.

I thought the working time for this resin was ~15m, but it's still very much a liquid.

Also my quick mold assembly also spung a leak, whoops. -_-

I've put this into the oven to bake at 60°C . Heating polyurethane can speed up cure time, at the expense of some shrinkage.

My initial fears have been diffused.
I'd feared the polyurethane would not set since it's quite old.

But after 5m in the oven it looks like it is indeed curing. This particular resin changes from a yellow liquid to a cream coloured solid.

Reasonably successful but not quite 100%.

This mold design has very in-efficient sprues, which relies on the vacuum chamber to pull these bubbles out and replace with resin.

Take 2

Take 3

Number 3 was rich in Part B, by ~20% the part is still a little soft, I'll see if it's okay after 24hrs.

Parts are looking good! Most have some small bubbles that formed in a specific area of the mould.

One way to remove these would be to place the mould into a pressure pot to cure, this will shrink any bubbles down.
Unfortunately I do not own something capable of that just yet :(

If anyone was wondering, these parts fit inside the GPS dataloggers, and act as a PCB wedge, light pipe, and button.

I've painted the lightpipes black to reduce light bleed.