Mirror making.

[Sfarndell]

Hi Graham

I just came across your post on a search for something else. If you have the determination, don't give up!

Having a 10" dob and a 12" SCT in my stable of instruments, I punted large with my 1st (and only!!) mirror and went straight into an 18", 1" F4.5 (yup!) mirror. I hand ground and polished, and finished off with a perfect sphere (no astigmatism). Since I was a complete noob, I had the shape and astigmatism checked by experienced mirror makers at my local club. The mirror is currently about 50% parabolised with no astigmatism and I hope to finish it in the next year or so once other DIY projects are done.

It's a lot of work though: I kept a detailed log and so far it's taken over 90 hours of grinding and polishing to reach my current stage. If I get the figuring right it's still another 10-20 hours to go excluding cool-down and testing times, lap making/shaping, etc.

Good luck, and please post progress on the forum!

[Beulah]

I punted large with my 1st (and only!!) mirror and went straight into an 18", 1" F4.5 (yup!) mirror. I hand ground and polished, and finished off with a perfect sphere (no astigmatism).

Goodness me!! :eek: :eek:

Well done!

[Ericgraham]

18" is much too large for a first mirror! I'm glad you're proving the experts wrong. Keep on posting

Eric

[fwm891]

On testing: I've used two for 'testing' Foucault and a wire test. for general surface shape I used Ronchi. I could never feel comfortable with the ronchi test as a quantitive, data gathering test. The wire test for me was the most sensitive.

[woodbob123]

As someone who took the glass in one hand and hope in the other!!!! polishing a 24" x 1" thick blank aiming for f5. my first one and so far spent 3 years on and off getting this far. almost ready to clean out worrkshop and do final polish and begin testing so have been reading this topic with interest Used a machine to do the work one of the things I did was use a sheet of tufnel as a fine grinding tool and it seemes to have done a good job! should have a fouchart tester ready in the next week so you can then expect a loud cry of help what do I do next coming from SE Wales.

Spent my working life in industry fixing anything and everything so have the manual skills but no experiance of working to these tolerances but do enjoy a challange it's amazing what a bad case of apature fever/envy will do to a person

[Astrobits]

Interesting to see how this performs when you finish it. A mirror of that size, f ratio and thickness will loose 7.5mm so the centre of the mirror will be only 17.5mm thick, maximum! That's if you haven't ground out a bit more to get the curve right. You might well have big problems supporting the mirror while figuring it. Good luck.

Nigel