12" mirror making: take testing seriously
I’m around 10 hours into polishing, and it looks like I’m very close to polished out! I can see barely any tiny pits under a microscope. I think I’m done.
Next up, figuring. I can test a mirror’s shape easily. I have been doing that already despite not quite being done with polishing.
The problem with a thin mirror is that glass (and anything else) will happily bend a few hundred nanometers under its own weight. Leaning my glass mirror against a wall means all the weight is placed on one point, causing visible distortion. I need to remove that to isolate any real astigmatism. I need to build a structure that holds the mirror while resting its weight across many different points so it doesn’t flex, called a “mirror cell”.
Telescope mirror cells are usually made of metal and involve triangles on triangles that can move and turn. This is a solved problem for big telescopes, but usually involves metal parts. I haven’t worked with metal before; usually just 3D printing. Designing this will take some thought.