I love this kind of making!! This week assignment is great and this is an easy way to fabricate new fabulous parts. I used to use Smooth on Material to do these kinds of making
As starting, I designed a simple object (Coin) using Onshape to print it out and then make the mold after printing to make another copies by casting the mold
You can get STL file by clicking here
Then, as I planned, I open the file after exporting stl version from Onshape website, I opened the file using Cura to make the settings and get the g code ready to print