Assignment #15
moulding and casting

The fifteenth Fab Academy assignment is about making a mould and casting a shape. I usually try to connect assignments to my final project, but this technique does not seem necessary for it. Instead, I decided to design a button that could be cast in silicone or another material. Perhaps it will be useful one day!

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1 – 3D modelling the mould

The first thing I did was to use FreeCAD to model my button. This was done just by using pads and pockets. Then I used some boolean operations to generate the moulds.

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2 – Preparing the G-code

Once I was happy with the models, I switched to BlenderCAM, a Blender add-on that generates a wide range of milling paths, including finishing paths that were not yet available in FreeCAD’s Path workbench at the time. The version I used runs on Blender 2.76, which is available in Blender’s archive. I used a 3 mm flat end mill for this job. I imported my 3D model in OBJ format, adjusted the settings until I was happy with the paths, and exported the G-code using the LinuxCNC post-processor. My machine could read it without problems.

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3 – Milling the molds

Next, I milled the parts. I used hot glue to attach the wax block to the machine bed, imported the G-code into UCCNC, and started the job. The machine cut through the wax like butter, and it was satisfying to watch. When it finished, I brushed the remaining wax flakes off the moulds.

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4 – Pouring the silicone

Once the wax mould was clean, I used a two-component casting material to make the flexible mould. After mixing, the components gradually set.
The material I bought is called “Raytech Magic Gel”. It is generally used to seal outdoor electrical installations. The datasheet is available Here
I wore gloves and worked in a well-ventilated area. The instructions called for mixing the components for two minutes and indicated a setting time of five minutes. I mixed the components in a cup and poured the mixture into the moulds. To help release the flexible mould from the wax, I coated the wax with a mixture of dish soap and alcohol. I used a bolt to create a pouring channel. I waited 15–30 minutes before removing the flexible mould. I really liked its texture and softness.

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5 – Making the button

To save money, I had bought only a small quantity of casting material and was afraid there would not be enough left to make a button. Instead, I melted some of the wax flakes left over from milling to cast the final object. Wax is probably not ideal for a long-lasting object, but it worked well for this test. Since the mould was transparent, I could watch the wax change from a clear liquid to a white solid.

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Source files

Here are all the source files for the moulding and casting assignment:
1 - mould A
2 - mould B
3 - FreeCAD file