My wife is a Para-Professional who works in an 8th grade science classroom. To keep up with the kids, she does the classwork and homework like they do. (PS: I'm a former JH science teacher...)

Last night, she was drawing Bohr diagrams (they show the electron orbits and the number of electrons in each orbit) and she needed a template to draw the circles.

https://en.wikipedia.org/wiki/Bohr_model

I made her one. Now I'm making a set for the classroom.

Print flat, no raft, no supports. The template part is .75mm thick. Make sure that your shells will print that solid.