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Not flat but similar idea https://www.cmog.org/article/hale-reflecting-telescope-palomar https://www.cmog.org/article/hale-reflecting-telescope-palom... Imagi

Not flat but similar idea https://www.cmog.org/article/hale-reflecting-telescope-palomar https://www.cmog.org/article/hale-reflecting-telescope-palom... Imagine hand grinding telescope lenses https://www.youtube.com/watch?v=MjUcBWYVF9s https://www.youtube.com/watch?v=MjUcBWYVF9s

hinkley 7y ago
From what I understand, hand-grinding small mirrors is down to process as much as skill. Solid grinding compounds, once they start to wear, end up wearing themselves too. If you keep the pieces moving just so, you can eyeball a rough radius with the grinding material, and it will smooth itself out while smoothing the glass until they mate up. Basically once you have a wheel with a high precision axle, you can make lots of curves or straight lines.
HeyLaughingBoy 7y ago
Thanks for the reminder. About 25? years ago I bought the book How to make a Telescope and two six-inch blanks and grinding materials and set off to grind my own mirror. I never finished (it was super boring and really humid in the basement of my rented apartment) and I have no idea where the "blanks" are anymore but now I live in an area well outside of town where I can see the Milky Way with the naked eye if my neighbors turn their lights off so it might not be a bad project to restart. Bonus: I have the room to build a grinding machine so I don't have to do it all by hand.
CliffStoll 7y ago
Today, large telescope mirrors are finished using ion figuring: neutral atoms are shot at the surface of the mirror blank, for a precision ablation of a few angstroms. This works especially well for hexagonal mirror segments, because you can control the surface shape right to the edge of the mirror. Mechanical figuring (using ceramic or glass blanks) has troubles near the edge.
Sharlin 7y ago
Hand grinding telescope lenses (well, usually mirrors) is a fairly accessible hobby; you need patience more than anything else. It’s amazing how little technology you need to attain sub-micrometer precision.
- DanBC 7y ago
  I like this video from John Dobson about handmade telescopes, where he builds a complete telescope including hand grinding the mirrors. https://www.youtube.com/watch?v=snz7JJlSZvw https://www.youtube.com/watch?v=snz7JJlSZvw

hinkley 7y ago

From what I understand, hand-grinding small mirrors is down to process as much as skill. Solid grinding compounds, once they start to wear, end up wearing themselves too. If you keep the pieces moving just so, you can eyeball a rough radius with the grinding material, and it will smooth itself out while smoothing the glass until they mate up. Basically once you have a wheel with a high precision axle, you can make lots of curves or straight lines.

HeyLaughingBoy 7y ago

Thanks for the reminder. About 25? years ago I bought the book How to make a Telescope and two six-inch blanks and grinding materials and set off to grind my own mirror. I never finished (it was super boring and really humid in the basement of my rented apartment) and I have no idea where the "blanks" are anymore but now I live in an area well outside of town where I can see the Milky Way with the naked eye if my neighbors turn their lights off so it might not be a bad project to restart. Bonus: I have the room to build a grinding machine so I don't have to do it all by hand.

CliffStoll 7y ago

Today, large telescope mirrors are finished using ion figuring: neutral atoms are shot at the surface of the mirror blank, for a precision ablation of a few angstroms. This works especially well for hexagonal mirror segments, because you can control the surface shape right to the edge of the mirror. Mechanical figuring (using ceramic or glass blanks) has troubles near the edge.

Sharlin 7y ago

Hand grinding telescope lenses (well, usually mirrors) is a fairly accessible hobby; you need patience more than anything else. It’s amazing how little technology you need to attain sub-micrometer precision.

DanBC 7y ago
I like this video from John Dobson about handmade telescopes, where he builds a complete telescope including hand grinding the mirrors. https://www.youtube.com/watch?v=snz7JJlSZvw https://www.youtube.com/watch?v=snz7JJlSZvw