I tried to find a printable Solar Eclipse Viewer on Thingiverse, but I could not find one...so I made this one. Here are the steps to use it:

1. Print both parts
2. On the open-end of the "base" tube, wrap some aluminum foil tight, and place the "cap" piece over it to hold it together.
3. Poke a small hole in the tin foil with a needle, tooth pick, or paper clip.
4. Point the cap end toward the sun in an eclipse and you should see the outline on the solid side of the base, through the view hole.

Unfortunately, as of creating this, this Eclipse Viewer design is completely untested, but after testing on the upcoming eclipse, I'll make modifications if needed.