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My grinding tool is making cool patterns!
You’re looking at water trapped under my 12" meniscus mirroe, and flowing between the channels in the home depot porcelain tiles on my grinding tool. Those tiles will grind flat eventually.
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I got a table for $5 at a yard sale. It looks perfect for a mirror grinding setup after putting some weights on the bottom rack.
Now that I’ve completed my 8" mirror polishing, it’s time to try my bigger telescope mirror project. Just making this blank took a lot of effort - now, to grind it.
12" meniscus mirror: Grinding start!
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Taken using my 4.5" telescope and phone! Both Mars and Jupiter fit into telescope view!
Very annoying observing session. Tried to take photos of the ring nebula but missed; planet conjunction was extremely slightly out of focus and I didn’t see until morning, and I looked for but still couldn’t see M33. Couldn’t see any detail on mars by eye either; that should change as we get closer to opposition.
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Someone brought an extremely accurate “double pass autocollimator” tester to an amateur telescope maker meetup… and it showed an uniform shade of gray across the whole mirror, meaning no defects (ignore the circular reflections from the test stand). That means my mirror is an extremely smooth parabola! I’m done mirror grinding!
🎉 First mirror: complete! 🎉 That’s so cool! I thought I was slightly overparabolized based on my Foucalt testing.
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Unable to find image 7164387-8-mirror-actually-image.png Unable to find image 7164387-8-mirror-actually-image2.png Someone brought an extremely accurate “double pass autocollimator” tester to an amateur telescope maker meetup… and it showed an uniform shade of gray across the whole mirror, meaning no defects (ignore the circular reflections from the test stand). That means my mirror is an extremely smooth parabola! I’m done mirror grinding!
🎉 First mirror: complete! 🎉 That’s so cool! I thought I was slightly overparabolized based on my Foucalt testing.
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8" mount v1 complete!
After several days of designing, 3D printing, and experiencing the joys of my favorite telescope related activity, hacksawing through metal, I managed to assemble a complete mount! Design-wise, I had to replace 0.5" screws with 0.75" screws in a few places because the redesigned EMT tubes were too close together. The telescope uses only 0.5" screws, so it would have been nice to match, but it’s fine for an one-off.
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I did a tiny bit more parabolizing, then re-measured my mirror. Last time, my spreadsheet and measurements told me my outer zone needed to focus tiny bit farther and my lower zone needed to be a tiny bit closer. To dig the inner zone out, I did some W strokes with lots of mirror movement on the tool edge, and then used long center over center strokes with a tiny offset to dig everywhere but a tiny strip of outside.
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Unable to find image image2_1.jpeg Unable to find image image2_1.jpeg I did a tiny bit more parabolizing, then re-measured my mirror. Last time, my spreadsheet and measurements told me my outer zone needed to focus tiny bit farther and my lower zone needed to be a tiny bit closer. To dig the inner zone out, I did some W strokes with lots of mirror movement on the tool edge, and then used long center over center strokes with a tiny offset to dig everywhere but a tiny strip of outside.
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I got the news from my local glass studio in an all-caps email that said nothing but “IT WORKED!”
Look at this! My glass is now clearly curved, around 1/4" taller at the sides than at the center! That’s very close to f/4, my goal! SLUMPING DRAPING: SUCCESS
Weirdly, even though the mirror is the right shape, the cement form seems to have warped. The top face is now flat, and the bottom is now curved - which is weird because originally the bottom was flat and the top was curved.
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