Filament Riveting Tool

For my last project (https://www.thingiverse.com/thing:2754147) I used a short piece of filament for the pins in the hinges. To keep them in, I used a hot air gun to heat up the blade of a knife. Then, I pressed the side of the blade to the end of the filament and melted it until the diameter was about 50% larger than the original O.D. This was functional, but I didn't like the flat end and the sharp edge that it made.

So, I decided to make a tool who's sole purpose is to form a button, or