Help Wanted with C8 - Loose Nut

[moondog]

I've just bought a Rigel red dot finder to fit to the C8

I wanted to fit it to the tube by removing an existing screw at the back of the C8 tube and replacing it. I thought I could use a screw hole on the opposite side of the tube to the standard finder.

Problem is, when I turned the screw ony a couple of turns I heard the dreaded 'clink' - yes, there's now a small nut resting inside the tube!

I obviously chose the wrong screw hole!

Any advice on how to rectify the problem would be welcome

MD

[Kai]

If you very carefully take the corrector plate off (after marking its position) , wind back the primary mirror and tilt the scope you should be able get to the loose nut and reattach the nut and bolt.

HTH

[Jeff RV]

If you are brave enough to attempt this.. be extremely careful, as i was reading a post on Cloudy Nights the other day, were all didn't go quite to plan for some poor chap.

The end result was a broken corrector plate (expensive), he evidently forgot to lock the dec axis or something, momentary turned his back and wallop.

Jeff.

[Psychobilly]

I am sure this has come up before and a drinkign straws thread and small magnet solution suggested....

Thats if you can see the nut in there....

Peter....

[Daz1969]

Hi there, The same thing happened to me a few yrs ago !

I got hold of a fairly big magnet and slowly moved to the back of the scope where i got it out of the rear cell(Very slowly and carefully)worked for me !

Good luck

Daz:icon_salut:

[moondog]

Thanks for the quick response guys.

I'll give it a go - ensuring the Dec axis is locked first!

I need to clean the corrector plate (carefully!) anyway.

Daz - it's not just getting the nut out that's the only problem it's fitting it back!

MD

[Jeff RV]

Thanks for the quick response guys.

I'll give it a go - ensuring the Dec axis is locked first!

I need to clean the corrector plate (carefully!) anyway.

Daz - it's not just getting the nut out that's the only problem it's fitting it back!

MD

Then it may be better remove the ota from the mount and work with it on your bed just in case, i know i would.

Just a thought!!.

Jeff.

[Psychobilly]

watch the shims when you take the corrector plate out they need to go back in the same place... and also get a feel for how tight the screws holding the plate in are done up.. you wouldn't want to over tighten them when it comes to putting them back...a and undo and do them back up in a cross pattern like wheel nuts...

Peter...

[moondog]

Thanks for the comments. Since I've never done this before I Google'd it to see if I could find any detailed instructions and pics on taking a C8 to pieces. Found this link:-

Astromart Articles - Disassembly of an SCT: Child's Play

MD

[Psychobilly]

Like most of these things if you prepare the work area.. and use a methodical approach then they are ok....

Peter....

[moondog]

JOB DONE!!

Corrector plate removed, nut caught and fitted.Corrector plate cleaned both sides.

Refitted - no bits left over!

Scope tested outside and shows no obvious visual defects.

Will have to check collimation when I get a decent night.

Only slight problem was getting the corrector plate 'unstuck' from the sticky black tape holding it in place. Took the shims out first and the corrector then came easily away.

Thanks for the help.

MD

[Psychobilly]

Nice one

[Jarndyce]

Well done MD!

Sweaty palms or wot!

Couple of questions, if I may...

What did you use to clean the corrector plate?

Any chance of a pic showing which screw you removed? As a warning to others...

[moondog]

Yes - a few sweaty moments!

The Orion Optical Cleaning Kit. Just used the cleaning fluid and the optical tissues from the kit.

Small amount of fluid on one tissue. Clean from centre to edge in approx. 45 deg sectors. Wipe with another dry tissue. Replace with new tissues. And so on round the corrector plate. I used almost a full swatch of tissues in the process.

Looking inside the OTA I would say don't try to remove any screws from a C8, or you could have the same problem!

In the end I used the supplied double sided tape to fix the Rigel Quickfinder - which is incidentally excellent and gives you a 'bull's eye' red target instead of the usual red dot.

MD

[moondog]

When I'd finished putting the scope back together, I did an initial collimation in daylight using the 'Bob's Knobs' method.

Then last night I collimated the scope on a Mag 2 star @ 220x and it looked OK.

Will have to check it against a Mag 3 star @ 400x with the web cam if I can get a good sky. I know it's going to need a few more small tweeks to get it spot on.

MD