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Celestron 127 SLT Mak mirror fell forward

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#1 daniel_h

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Posted 01 November 2014 - 09:50 PM

got a 127 off a guy -somehow i think he was thinking of upgrading to electric focuser , but somehow the focus knob fell off & allowed the primary mirror to slide right to the front 1/3 of the tube [see pic1]

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Edited by daniel_h, 01 November 2014 - 09:51 PM.


#2 daniel_h

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Posted 01 November 2014 - 09:55 PM

i go the back off & after much pulling [the primary baffle was stuck to the back of the corrector] i managed to slide the primary back down into place & secure the focus know in place

 

nothing apart from the focuser knob appears to hold the primary mirror to the back of the OTA

 

pics show the baffle etc..there is some thick black goo on the baffle, which now sits on the back of the corrector..does anybody know how to get the corrector off, there apears to be no screws so m guessing the whole assembly screws off -i just cant get it to budge?

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Edited by daniel_h, 01 November 2014 - 09:59 PM.


#3 daniel_h

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Posted 01 November 2014 - 09:56 PM

lastly a shot with mirror towards back of OTA

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#4 daniel_h

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Posted 01 November 2014 - 09:58 PM

oops forget the inside back panel pic

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#5 hardwarezone

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Posted 01 November 2014 - 11:46 PM

here is a youtube video that details how to take off the front corrector.

 

http://www.youtube.c...h?v=JjFAzQZUR9Y

 

I took mine off once with bare hands but I did it on the floor and bed. Don't like high flying stunts. Get somebody to help you hold the tube.

Part of the threads had black paint on it making it hard to twist. Lots of squeeky sound.

When you screw it back on, note the thread count it must be 3 top 3 bottom to avoid cross-threading.


Edited by hardwarezone, 01 November 2014 - 11:48 PM.


#6 daniel_h

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Posted 02 November 2014 - 12:52 AM

great tip -i have one of the oil filter wrenches the guy uses, ill give it a try



#7 daniel_h

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Posted 02 November 2014 - 01:35 AM

the oil filter wrench did the trick, here are some pics showing the baffle tube felt/glue & after most of it has been cleaning with zeiss wipes [i need to hit the last bit of glue with some acetone tomorrow]

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#8 hardwarezone

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Posted 02 November 2014 - 03:24 AM

Thanks for posting photos of your experiments, I thought about removing the secondary baffle to reduce the central obstruction by 7% but the residue looks unacceptable for me.

#9 daniel_h

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Posted 02 November 2014 - 04:28 AM

normally the secondary baffle wouldnt contact the secondary, in this case the mirror fell forward--im not sure why celestron have used so much goo/grease on the baffle tube--it seems unnecessary tome unless im missing something



#10 Asbytec

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Posted 02 November 2014 - 05:11 AM

Daniel, yea, that looks like a lot of residue. I am sure it will come clean, it'll just take some careful cleaning.

 

When I removed my baffle, the foam ring came up easy by getting something gently into it and peeling it away. It peeled fairly cleanly, and the remaining residue cleaned up completely.

 

Thanks for the tip for removing the meniscus. I was trying to clean an ETX and had the same problem. Never did figure out how to get it off without breaking it.



#11 Eric63

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Posted 02 November 2014 - 10:11 AM

Daniel, I'm looking forward to your first light report with the removed baffle.  After reading what Norme did to his scope and how others have flocked their tubes, I keep thinking of opening the front end and being adventurous myself :grin:

 

Eric



#12 dweller25

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Posted 02 November 2014 - 10:56 AM

Hello Daniel,

 

Don't know if you have seen this thread.......

 

http://www.cloudynig...v/#entry4717586

 

But if not it will help you to collimate the back end when you rebuild it.



#13 Ed D

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Posted 02 November 2014 - 11:29 AM

Daniel, thanks for posting what I find to be very useful info on these OTAs.  I'm also looking forward to your report after the baffle removal.  I removed my front corrector assembly on mine, which was also extremely tight.  (I plead the Fifth on how I did it.)  On reassembly I coated the threads VERY SPARINGLY with light grease.  I carefully aligned the threads and screwed the corrector assembly until it just made contact with the tube, very lightly snug.  Alignment of the Meniscus is now perfect and stays that way, no ill effects from lightly snugging it down after extended use.  Star testing shows perfect alignment in spite of having removed and reinstalled the assembly many times.  I'm sure the extreme tightening was stressing the meniscus assembly and/or tube in my scope.

 

Here is a link to a post I made that gives dimensions for working aperture, central obstruction, etc.  LINK  These not so little scopes are awesome performers.

 

Ed D



#14 gene 4181

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Posted 02 November 2014 - 12:06 PM

kudos to ed Holland, what a thorough thread on the disassembly of the 127 mak.



#15 ChristianG

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Posted 02 November 2014 - 08:03 PM

Hi.

 

I may have missed this, but why actually did you remove the secondary baffle? Was it knocked out of alignment/damaged by the primary? In those telescopes, the secondary baffle serves a purpose. You will need a dew/light shield that is at least 12" long (as I measured on mine) if there is no secondary baffle.

 

--Christian



#16 Ed Holland

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Posted 02 November 2014 - 09:51 PM

Interesting thread.

 

Daniel - I'm glad to see that you are getting the scope back into shape. Do you intend to replace the secondary mirror baffle or leave it off?

 

It's probably worth, as you've noted, removing some of the excess grease from the system. It is not neccesary and can end up in places where it is not welcome.

 

When you replace the focuser knob, it is important to ensure there is no in-out play, as this translates to slop in the primary mirror position. On my scope, someone had rempved and replaced the knob without checking this, and at first I coudn't work out why the scope wouldn't focus properly or hold focus.

 

Fortunately these telescopes are robust and easy to work on once one knows their quirks. If you get things right now, you'll probably never have to touch it again!

 

Cheers,

Ed



#17 daniel_h

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Posted 03 November 2014 - 12:59 AM

ah thanks ed i do have some focuser play -how did you fix this..

 

i intend to leave the baffle in place for now, my main reason for taking the ota apart was to remove the felt/glue from the secondary mirror which had originated form the baffle tube, & i think i will remove most of the goo -& lightly grease the baffle tube which the primary rests uon



#18 Ed Holland

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Posted 04 November 2014 - 12:11 PM

I was a bit confused when first looking at your pictures of the back of the telescope, but now I realize what you did.

 

The normal procedure for disassembly is to unscrew the whole rear cell assembly from the main tube. You removed the collimation screws, which allowed the outer part to come free, but not the inner plate that is threaded into the tube.

 

To assemble the focus knob correctly, you'll need both parts of the rear cell free, and reassembled. No fine tuning is necessary, or possible at this point. Bring the mirror back so that the focus spindle comes through the backplate, and fit the knob whilst maintaining pressure to squeeze everything together. The o ring on the brass spindle allows for a little compliance in this assembly, and for a nice smooth feel to the focus action, but needs to be pre-loaded as you replace the knob. Firm finger pressure is all that is required, not a death grip :). This is what will eliminate fore-aft play, except perhaps for what remains in the threads of the focus mechanism. I fitted a spring between the backplate and mirror bracket to help with this, and it has been reasonably effective, but that is a minor consideration.

 

After this you'll want to re thread the whole back assembly into the tube again. Clean both sets of threads  - they tend to gall a bit and make lots of metal dust which can rattle around in the tube ever-after. Apply a sparing film of grease. This aids in assembly - the re-threading can be a bit awkward - and should prevent galling & generation of more debris, or at least trap it so it doesn't plague the optics. Please refer to my other notes here http://www.cloudynig...v/#entry4717586 for a tried and trusted reassembly and setup procedure.

 

Good luck and well done for saving another of the classic 127 Maks

 

Cheers

 

Ed



#19 daniel_h

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Posted 04 November 2014 - 04:09 PM

thanks Ed, ill take it apart again


Edited by daniel_h, 04 November 2014 - 04:11 PM.


#20 labmand

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Posted 04 November 2014 - 06:25 PM

Thanks Ed for your posts, good stuff, have a Desert scopes 100mm f14 mak, think maybe same as

The Apex just rebranded, but not sure, anyway when I got it I was not happy with the image shift, removed

The back cover but the back plate would not budge so put it back togeather, tried again, bought a helical

Focuser but didn't really work that well so put it back in the box, but after reading your posts I gave it another

Shot, ends up the baffle tube was a little loose so the primary mirror had some play, tightened it up, cleaned and

Relubed, put back togeather, daytime testing shows zero shifting of a very smooth focus, outstanding, you guys

Are great, thanks so much for asking the questions and thanks to the guys in the know that are kind enough to

Share with us out here.

 

Update... outside, star and moon testing shows 0 image shift now and collimation

Stil looks good after all that was done, anyone know if this mak is a clone of the

Nexstar or Apex brands?


Edited by labmand, 04 November 2014 - 09:53 PM.


#21 hardwarezone

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Posted 04 November 2014 - 10:48 PM

Nexstar or Apex brands?

e, anyone know if this mak is a clone of the

No, it is not made by Synta.



#22 daniel_h

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Posted 05 November 2014 - 04:32 PM

i didnt pul the ota apart yet but did briefly check out the moon the view seemed fine, i just had a quik look -went to just over 100x



#23 labmand

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Posted 22 November 2014 - 02:44 PM

Norme said  "a lot of residue. I am sure it will come clean, it'll just take some careful cleaning."

If this residue/sticky glue gets on the main mirror, how would it be removed or should it be left

In place to avoid making a mess of the primary? Anybody? Thanks



#24 daniel_h

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Posted 22 November 2014 - 10:55 PM

if the glue was on the man mirror i would clean the same way -i usually start with something like zeiss lens wipes -then proceed to EtOH, finally acetone..then wipe wih water to finish. i wouldnt leave it in place  -it can't be good for the mirror coating & im not scared about cleaning optics 



#25 Asbytec

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Posted 23 November 2014 - 06:18 AM

Norme said  "a lot of residue. I am sure it will come clean, it'll just take some careful cleaning."

If this residue/sticky glue gets on the main mirror, how would it be removed or should it be left

In place to avoid making a mess of the primary? Anybody? Thanks

 

Mine came clean with a lot of soapy water and some acetone. Acetone first, then cleaning with soapy water to clear the residue left by the impure acetone. If I remember correctly, that's normally how I clean it anyway. I didn't have that much, but there was some left after peeling away the foam ring. 




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