After downloading the STL the next step is to 3D print the cup. This can be done with different end results in mind. In this explanation, we assume that you are using an FDM printer.
3D print for direct use:
To prepare for 3D printing use the slicer tool of your choice that is compatible with your 3D printer. Make sure you manually add at least two extra shell layers in the print settings. The first print we made was not waterproof, and adding extra shells solves this problem. Tweak a little bit for the best settings.
Choose your plastics wisely. The softening temperature of PLA is very low (60°C / 140°F) so boiling water makes it soft. ABS is better resistant but still the softening point (105°C / 220°F) is only slightly above the boiling temperature of water. Not so much is known (to us) about the chemicals that are released in these processes.
It is highly recommended to use food-safe plastics instead. Companies exist that produce such food-safe 3D printing plastics.
For more information about 3D printing and food safety check this post.
3D printing for clay casting:
When you want to use the cup to cast a plaster mould, you don’t need to add extra shells. More important is the print quality. To make the casting of the plaster mould somewhat easier we developed a mould-frame. You can find the 3D print files here. We made a couple of small adjustments to the cup for the clay casting. At first we raised the bottom part to make the bottom hollow and second we made a tiny hole for our wooden helper stick that keeps the cup in place while casting the plaster. See the page ‘Mould and clay casting’ for more info about making the mould.
3D printing using a Prusa I3 MK3.
Screenshot of a cup in 3D software. Create a hole to help in casting the plaster mold and raise the bottom part to make the bottom hollow.