This is a quick 3D printed ring that I made with my son. The skull part is made of 2 parts (box and lid) so that you can store little items in the skull for fun (or maybe stick an LED in there with a small coin cell battery for a glowing cool effect). All objects were 3D printed on my Printrbot Simple Metal. I will share my settings, but your settings may vary depending on your machine and filament type.
Step 1: 3D Printing
The Skull Box
I skull box can be found at http://www.thingiverse.com/thing:121972. It prints in 2 parts (lid and box) and snaps together to make a little hidden compartment. I used a raft for printing support on mine, just so that the small part would be less likely to curl and warp (since the 2 pieces have to fit snugly together, the less warping the better). I scaled mine down to 30mm on the x axis (that is for both pieces though, so basically cut that in half for each part of the box). I printed at the highest resolution that my machine would print (100 microns) and went slow (20 mm/second) to help maintain detail and fill density at 100%. I used white translucent PLA filament, and it seems to extrude at 195 celsius nicely.
The model for the ring can be found at http://www.thingiverse.com/thing:167081. I scaled the ring down to 17mm on the x axis since this was going to be for my sons pinky finger. This can be sized to whatever will fit you best though, and the skull can be sized up or down accordingly. You'll notice that I added a brim support on the ring (just to make sure it didn't topple over during printing, it probably would have been ok without it though). I kept the other settings from the skull the same (fill density at 100%, speed to 20 mm/second, layer height to 100 microns etc...). I did have to rotate the ring so that the flat side was facing down on the build plate as it will print better in that orientation, but other than that I didn't have to do anything to that model.
Step 2: Finishing the Ring
To finish the ring, I hit the real rough spots with a dremel sanding drum (not too much, the high speed of the drum tends to melt the PLA), and then I finished it off with some 180 grit hand sanding to smooth everything out. Once I had the finish as smooth as desired, I just put a drop of super glue on the flat oval portion of the ring, and stuck the box portion of the skull on the ring (it cures quick, so make sure you place it where you want it right away, not much time to move it around). Then you can snap the skull face onto the box and you're ready to go.
Step 3: Finished Ring
This was a quick fun project, I let my son pick the design and we worked together to put it together. My son was very excited to enter this into the ring contest, so if you like it, vote for us!