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Meade MTS SN6 - how to defork?

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#1 sunrag

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Posted 19 September 2020 - 01:36 PM

I picked up a nice Meade Schmidt Newt SN6 from an ad on Craigslist. It is in excellent condition. I don't have a photo but it is identical to the photo I got of the internet.

I can take the OTA+Fork apart from the base mount by unscrewing 4 screws at the base. Ideally I would like to separate the OTA from its fork, as I want to be able to put the OTA on my HEQ5.

Is the defork easy and reversible?

 

Thanks for reading!

 

meade-sn6.jpg


Edited by sunrag, 19 September 2020 - 01:36 PM.

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#2 AlMuz

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Posted 25 September 2020 - 06:43 PM

I got the same scope on CL 3 month ago and put some time to clean it up and restore RA drive (mine had AC clock drive).

To defork:

  • Mark orientation (with a sharpie) and remove the mirror cell unscrewing 3 bots at the back
  • Remove corrector lens with secondary assembly, try not to rotate secondary assembly in the corrector lens central whole.
  • Put all removed optics into a safe place
  • Using alen key unscrew fork side-beams from the fork base (two bolts at the bottom on each side)
  • Now unscrew knobs at the setting rings, so then the side beams can be taken off
  • The last thing left is to remove tube flanges which are mounted from inside of the tube using (as i remember Philips head screwdriver is what you will need here)

 

Keep attention to put the mirror and corrector back in the same orientations as they were mounted originally, some say that manufacturer during the assembly might have rotated corrector when placed in a tube against the matched primary mirror to compensate intolerances of each other (I hardly believe that).

Make sure you know how to collimate Schmidt-Newt optics after reassembly.


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#3 jgraham

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Posted 25 September 2020 - 08:01 PM

It’s a good idea to mark the corrector before you remove it. I also like to collimate my SN before removing the corrector. If you put it back where it came from it should still be reasonably collimated. If you are careful de-forking is easy and reversible. I’m in the process of reforking an 8” SCT right now.


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#4 sunrag

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Posted 26 September 2020 - 12:52 PM

Thanks for the tips. I have deforked the SN6 but i did not remove the optics. The collimation as received was quite good, so I don't want to mess with that.

 

Do you have any way to fine tune the DEC position? I read in the manual that there is an option #66A for SN6 and #66C for SN8 to add manual control to the DEC axis. It is going to be tough to find these options now, but I am thinking of finding a worm gear (from McMaster Carr) that fits on to the DEC shaft.



#5 AlMuz

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Posted 08 October 2020 - 11:30 AM

Do you have any way to fine tune the DEC position?

I sold my scope a week ago, but here is an older picutre I've found:

MT-SN6
 
You see that knob in lower right corner of the fork - it turns a lead screw which moves the end of the lever inside the fork arm. At the top end this lever has a collar which goes around the the DEC flange of the OTA. The collar grip can be adjusted with preload screw.

Basically it works in a way of creating spring loaded torque on a DEC flang, which is enough to move the scope by few arc.sec per turn. It really helps in visual observations if you have your polar aliment slightly off and have a DEC drift. Otherwise (if aligned well) - you may live without it.

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#6 sunrag

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Posted 08 October 2020 - 05:02 PM

 

I sold my scope a week ago, but here is an older picutre I've found:

 
 
You see that knob in lower right corner of the fork - it turns a lead screw which moves the end of the lever inside the fork arm. At the top end this lever has a collar which goes around the the DEC flange of the OTA. The collar grip can be adjusted with preload screw.

Basically it works in a way of creating spring loaded torque on a DEC flang, which is enough to move the scope by few arc.sec per turn. It really helps in visual observations if you have your polar aliment slightly off and have a DEC drift. Otherwise (if aligned well) - you may live without it.

 

Interesting..so that is what the hole in one of the Fork arms for.

I don't have that knob or the lead screw. So this must be the option #66A.




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