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Old 18-09-2020, 06:44 AM
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PKay (Peter)
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Replacing Secondary Mirror Lightbridge 12inch

Hi All.

Advice needed.
I ordered and received a replacement secondary (CNScope) however we got the measurement wrong.
I needed 96mm measured the long way, but the mirror I have is 96mm the short way, in other words too big.

So can I cut it down?
I have a diamond water cooled glass grinder used for stained glass.
It might be a bit slow, but worth a try, I guess.

Thoughts?
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Old 18-09-2020, 06:55 AM
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mental4astro (Alexander)
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Only one answer here - buy a new mirror the correct size.

You will not be able to cut down the oversized murror you have without causing damage to the reflective surface. It is the quality of the finely worked surface and finish that we pay for.

Sorry for the bad news.

Oh, except if you are capable of refiguring the damaged surface to restore it to its original sub-wavelength condition and re-aluminize to the same finish, be it enhanced aluminium or protected aluminium. There are a couple of businesses that can do the re-aluminizing for you.

Alex.
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Old 18-09-2020, 07:07 AM
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multiweb (Marc)
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Cutting it yourself is a big no-no. Buy a smaller one if you must and sell this one to offset the cost. It's a 12" so your central obstruction although bigger might still be alright. Have you tried with this secondary first? Do you do visual or imaging?
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Old 18-09-2020, 07:51 AM
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mental4astro (Alexander)
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Good points, Marc
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Old 18-09-2020, 08:45 AM
Rainmaker (Matt)
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Quote:
Originally Posted by multiweb View Post
Cutting it yourself is a big no-no. Buy a smaller one if you must and sell this one to offset the cost. It's a 12" so your central obstruction although bigger might still be alright. Have you tried with this secondary first? Do you do visual or imaging?
Good advice
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Old 18-09-2020, 09:06 AM
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PKay (Peter)
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thanks chaps for replying.

I will purchase a new mirror the correct size.

In the mean time, bring out the angle grinder...

The scope is a highly modified lightbridge for imaging.

This project started a few years ago however then, I was using an EQ6 mount that didn't like it.

After recent purchase of an EQ8, the project is back on the bench.
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Old 18-09-2020, 11:02 AM
Saturnine (Jeff)
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Hi Peter
As the others have said, buying the correct minor axis sized diagonal is the best and only real option and the larger one that you purchased by mistake would probably be suitable for someone with an 16" F4.5 scope so you should be able to sell it to recover some funds.
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Old 18-09-2020, 12:00 PM
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multiweb (Marc)
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Quote:
Originally Posted by PKay View Post
In the mean time, bring out the angle grinder...
and don't forget the file for a nice finish.
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