Designing for 3D printing is a blast because occasionally you get these really groovy neat ideas that you can't wait to try out, and then you try it out, and sometimes it works, and sometimes it doesn't.
This is the story of a time it didn't work.
See, those coins I made last time I though would look better if the two sides had something distinctive about both sides. So I decided to cut little 0.1mm lines in a pattern in both sides. 0.2mm is the minimum distance you want to make things if you want them to separate. Of course separating wasn't my goal. I just wanted the slicer to have to trace lines in an otherwise solid surface. So I built some lines, used the solidify modifier to thicken them up, fought with the normals, fought some more with the boolean operator, and eventually had some coins that I thought would look pretty neat.
So I'm going to go back to flat, unpaterned prints. Less cool, but better looking.
However, I've got an idea that might fix that bridging on the bottom side...