My Quattro mirror clean fiasco.

[focaldepth]

I started my Astro journey in 2010 but due to no clear skies for over a year (clear skies being inversely proportional to my distance from a telescope), my observatory has been idle for quite some time.

Anyway, the BBC was predicting 4 clear nights in a row and I decided to have another go at imaging M81. Observatory de-cobwebbed. Sleeping Queen Wasp relocated. Floor vacuumed. Coffee cup bio-hazard sanitised.

The 1st night and following day was lost chasing a loose power cable and getting confused between a licensed and an unlicensed version of Nebulosity.

Anyway I collected some reasonable data despite a full moon and more light pollution than I remember.

The data had a lot of dust doughnuts so I decided that the mirrors must be due for a clean.

I read several guides on here and on the web and chose to remove the mirrors.

After removing the mirror cell from the 10" Quattro, I started removing the 12 clamping screws. Now the fun starts. 4 were very loose. 2 were very tight.

6 sheared off under very little torque.

I've lived long enough to know this is the point where panic is appropriate but have learnt that life goes on even if we stay calm. So Off to the mini mill.

After gently clamping the capsule on the bed with wood blocks to protect the alloy,

I centre drilled then drilled 2mm, then 2.5mm then 3.2mm holes in the old screws.

I then ran a couple of 3mm taps down the holes to clear out debris and went to get some screws from my fixings stash.

I had every size except 4mm. So off to Ebay for some 3mm x 35mm Allen button head screws.

After spraying the new screw heads a stylish matt black, the cell was reassembled.

Now that all 12 screws are a loose fit I am concerned that they will work loose.

This is a problem for another day.

Next I reassembled and collimated the telescope. It only took a few minutes to collimate, the last time I tried it took me ages to align the mirrors.

Now I wonder how many years until I see a clear sky again.

[ChrisLX200]

I'm sorry to have to tell you but... dust bunnies don't originate from the main optics, they are way out of focus. They are always associated with dust motes on the camera/filters etc.

ChrisH

[focaldepth]

Yes thanks,  ChrisH, I did clean the camera as well but that was another story.

I guess the point of the story was to warn of non removable screws in this model of scope.

[focaldepth]

Yes thanks,  ChrisH, I did clean the camera and filters as well but that was another story.

I guess the point of the story was to warn of non removable screws in this model of scope.

Living in high light polution I chase every bit of contrast I can. I also wanted to give the Flats less work to do in processing.

[Scott]

glad it's all sorted. maybe some lock tight on the screws will stop them from coming loose?

[Steve Ward]

Better to use some lock washers , Loctite caused the original problem.

[Scott]

ahh, I see...I was assuming (probably wrongly) they were "cold welded". sorry for the bad advice.

[focaldepth]

Lock washers wont really work because they will need to be screwed down on to the rubber mirror supports.

I think that lock tight may work now I have stainless bolts and not chineese chese ones. I will experiment on some scrap metal some time.

[focaldepth]

Oh and thanks agan to ChrisH.

Something you said made me realise that I need flats for each coloured filter. (I have always taken a short cut and used RED before I start imaging). The original problem I had was dust spots on one filter not being calibrated out by the flats on another filter.

I could not figure it out till now.

[Steve Ward]

A little dab of silicon will stop them working loose , Loctite could well be a problem in the future as stainless screws tend to be weaker than standard ones in my experience.

[focaldepth]

I did not mention that the original screws were a very tight fit, in most holes. The new bolts were a very tight fit also. I felt that the threaded holes where undersized and tapered.

 

I don't know if this is normal or a production error. After running the taps through it feels like an M4 thread should.

 

The removed original screws had very chewed up threads for the last 1cm of the screw. My feeling was that they were not supposed to come out. They were also very brittle and weak some of the screws had obviously started to shear on assembly and only needed a little encouragement to fall apart.

There is also a long length of screw outside the thread which will allow twist outside the threaded hole.

 

[sex joke alert]

 

They say it takes an engineer to appreciate a really good screw.

 

[End Joke]

 

These were not good screws.

[Stu_2011]

A little dab of silicon will stop them working loose , Loctite could well be a problem in the future as stainless screws tend to be weaker than standard ones in my experience.

Indeed, it's a bit of a common misconception that "if it's stainless it must be good". Most stainless screws in consumer stuff out of China are based on the grade 304 or 301 and this grade is not very strong at all. A good high tensile steel bolt is much stronger and far better if loctite is around.

Stu

Sent from my iPad using Tapatalk

[Singlin]

I had exactly the same problem with my Quattro when removing the main mirror.

I sheared 7 screws and managed to unscrew them with pliers after heating the base plate.

I then replaced the screws with European grade ones.

[focaldepth]

The only reason I did not buy high tensile steel was most of them do not have threads along the full length.

 

I agree high tensile steel is stronger than stainless and plain steel is more flexible. However in this case all we need is a gentle pressure on the rubber mirror supports.

So the suggestion of a dab of silicon sounds good to me. I'll try it when I clean the mirror next year.

 

Working in the steel industry I soon learned that you should never use steel bolts in aluminium. Funny how all cars do, and telescopes and.... Stainless lasts much longer in aluminium. Not that there should be much corrosion inside a telescope. And this did not appear to be the problem here.

 

[iksobarg]

Thanks and sorry. I'm not having such a bad day anymore.

[russ.will]

Rather than loctite, I would advise copaslip on each screw, to stop the corrosion that binds a ferous to non ferous metal. I can't see why screws would work loose and the lack of tightness of some of them, was more likely down to SW assembly tollerances.

Russell

[uhb1966]

Oh boy... what an epic story... and i got me a quattro, too

...glad you could sort it out... i wouldnt know how to solve that