Grinding a 12.5-inch telescope mirror with 120 grit

Early stage of grinding a 12.5-inch telescope mirror blank with an 11.5-inch tool. The tool consists of ceramic tiles arranged on a convex surface that matches the curve of the mirror (roughly f/4 focal ratio). The abrasive is the very coarse 120-grit Silicon Carbide powder, which looks like black sand. Grinding this blank with the much finer Aluminium Oxide can be seen in my later video. Progress on this project is documented at http://astroscopy.wordpress.com Many thanks to the telescope workshop of the Santa Barbara Astronomical Union for making this project possible!

Category:

Science & Technology

Tags:

• astronomy
• telescope
• optics
• mirror-making
• telescope-making
• ATM

[balzerbarn]

Very nice pyrex disc, Im sure you put it to a nice shape.

[iutubeus]

@balzerbarn Thank you! Slowly getting there. Just got finished with grinding.

[zi6film]

Thats one thick mirror, i use 19mm glass for anything up to 16 inch

[iutubeus]

@zi6film You are saying my blank can be half as thick. Interestingly, according to an old classic -- "How to Make a Telescope" by Jean Texereau -- my blank should be twice as thick! (3 inches for a 12.5-inch mirror.) So I thought I was taking the middle road. :-)

[iutubeus]

@jamieball Must be. (I am still getting there myself.) What is neat is that -- given enough patience -- the result you can achieve by hand will be as good as any mirror you can buy.

[MiCompre]

You ought to do this indoors in a dust-controlled area. if your mirror gets scratches on it, you'll know it's because it got contaminated by airborne grit and stuff! I had blisters for weeks after \i made my 6" mirror in the 1960s.

Still have the polished blank somewhere! Good Luck.Enjoy your scope and its making.

MC

[foreilly1958]

@iutubeus How did your mirror come out?

[foreilly1958]

@zi6film You mut be in Europe. In the States we have substrates available to 1:6 thickness to diameter. It makes fo a more stable mirror and reduces mounting problems.

[jamieball]

Interesting, I hope one day to grind my own mirror.. it must be satisfying to achieve good viewing with a telescope mirror that you grinded yourself..

[zi6film]

@jamieball about 40 hours by hand to grind and polish a 12 inch mirror