Skywatcher 200PDS .. can't remove primary mirror - Forums

Topic starter

Aug 2, 2022 · Edited: Aug 2, 2022

I'm struggling to remove my primary mirror from my 200PDS Newtonian. I've removed all the screws that attach it to the tube, however it feels totally jammed. Any suggestions?

Reasons for doing this:

* Inspect the mirror and clean if necessary (although I don't think I need to)
* Maybe add a ring to it to prevent diffraction of stars caused by the mount clips
* Maybe flock the tube
* Maybe add baffles

I'll be careful to do only the minimum changes for now, but if I can't get it off I can't do any of them.

Well Written Engaging

Marc-Antonio Fischer

Aug 2, 2022

Andy Wray:
I'm struggling to remove my primary mirror from my 200PDS Newtonian. I've removed all the screws that attach it to the tube, however it feels totally jammed. Any suggestions?

I was scared at first too. You removed the 6 screws right? (tiny black ones around the tubus) try to twist and pull it. Sometimes its really hard. Make sure to do it on a planket or a soft ground, because you maybe need a lot of force.

Concise Supportive

Gerhard Rehak

Aug 2, 2022

The mirror sits very tight - pull gently but hard is the only advice. As mentioned above, use a blanket for protecting everything.

Mike Dobres

Aug 2, 2022

Andy

I'd recommend cleaning in place - I have a 14 " Dobson - I dont dare remove the mirror!. I choose a hot summers day, and place the tube horizonta- slight pointing down to drainl. I use a 5 liter pump sprayer, to first spray DI water with a drop-of detergent. Then rinse thoroughly with DI water using the same, sprayer. I use a hair dryer on cold, to chase the stubborn to chase droplets to the edge of the mirror. Much safer, and you don't have to worry about putting the mirror back correctly!

As for clips - you dont need to remove the mirror to add a ring - you can just place it placed against the mirror - or over the aperture. I just made one yesterday - was pretty easy to install and remove. Here's a few ideas on how to do it. Mine was just cut from cardboard and placed snug against the mirror - secured to the tube with 4 pieces of masking tape.

https://www.cloudynights.com/topic/656915-cleaner-stars-how-to-install-an-aperture-mask-on-your-newtonian/

CS

Mike

Helpful Supportive

Marten Amschler

Aug 9, 2022

Andy Wray:
I'm struggling to remove my primary mirror from my 200PDS Newtonian. I've removed all the screws that attach it to the tube, however it feels totally jammed. Any suggestions?

Reasons for doing this:

* Inspect the mirror and clean if necessary (although I don't think I need to)
* Maybe add a ring to it to prevent diffraction of stars caused by the mount clips
* Maybe flock the tube
* Maybe add baffles

I'll be careful to do only the minimum changes for now, but if I can't get it off I can't do any of them.

I had the same struggle during my first cleaning. The mirror cell fits very tight. Try rotating it and wiggle it around. You can actually apply quite some force. The white metal of the mirror cell is rigid and the mirror does not have direct contact to the Tubus walls.
it's a good thing to mark the position of the mirror cell and the Tubus. In that way you don't need to adjust too much during your next collimation.

Helpful Supportive

Andy Wray

Topic starter

Sep 2, 2022

Help! Try as I might I have been unable to get my primary mirror holder to move even one millimetre, let alone extract it from the tube.

Has anyone else had this problem and found a technique that works? I have applied as much force as I am physically able to and not a hint of movement.

Well Written Engaging

andrea tasselli

Frequent contributor

Sep 2, 2022

Possibly it is seized on the inner tube wall? Try to heat the tube up and turn the mirror cell around when the tube is hot.

Andy Wray

Topic starter

Sep 2, 2022 · Edited: Sep 2, 2022

andrea tasselli:
Possibly it is seized on the inner tube wall? Try to heat the tube up and turn the mirror cell around when the tube is hot.

I will try, but fear it is a lost cause ... it really IS that tight!!

That said, I think I can improve my secondary mirror alignment to minimise the issue. I still don't have the three mirror clips perfectly aligned with my focus tube.

Pixinsight reports my FWHM Eccentricity as 0.38 which is actually pretty good. Maybe getting my alignment improved as well as my tracking might get me somewhere close to where I need to be.