These are the design files to house a thermal printer. The printer is this model sold by adafruit.
Adafruit has already posted a laser-cut enclosure here, but wouldn't you rather print one off on your 3d printer??
This whole thing is part of a tiny piece of art which can learn more about here:http://maxlupo.com/the-thermal-printer-doorbell/
I am not ther person you want to try and write instuctions, and I do apologize about that. BUT this link will give you the source code for the arduino sketch which powers the project, as well as a circuit diagram so that you can try and build your own.
As a sidenote:
This started out as my first arduino and 3d printer project, and it kind of shows...anyway, for those of you with a smaller printer I have included the stl files as a set of 2 halves, which would need to be glued togther. If oyu have a large enough printer, I have included an 'un-divided' set.