Can't remove Skywatcher 200PDS primary mirror ... help needed

[andymw]

I need to remove the primary mirror from my Skywatcher 200PDS as it appears that one of the mirror clamps is pinching the mirror.  Try as I might though, the mirror is totally stuck in the tube (I have used plenty of force, but it just won't budge at all).

Has anyone else had this issue and , if so, how did you overcome it?

[alacant]

Assuming you have removed all the cross-head screws retaining the mirror cell (!), then probably because you still have the tube rings attached. These distort the tube.

HTH
 

[malc-c]

From memory, all I did was undo the (6 if I recall) screws around the base of the tube that holds the mirror cell in place and the whole assembly came out

 

[Spile]

I didn’t come across any issues when I took my mirror apart as per https://astro.catshill.com/mirror-cleaning/ I

 

[NGC 1502]

18 hours ago, andymw said:

Try as I might though, the mirror is totally stuck in the tube (I have used plenty of force, but it just won't budge at all).

I’m not nit picking here-  When you say you’re trying to remove the mirror do you mean the mirror cell complete with mirror as a single unit?

To remove the mirror cell complete with mirror you need to take out all of the screws that attach the mirror cell to the tube. The screws on the back surface of the cell are collimation screws and lock screws, leave those in place.

When the cell finally pulls away from the tube it may come free suddenly, so be prepared for that.

As mentioned above it’s possible that tube rings have distorted the tube enough to hinder what you’re trying to achieve.

Hope you sort it, Ed.

[andymw]

Just for clarity:

* I have had the tube rings removed whenever I have attempted the mirror cell assembly removal

* Yes, of course, I have removed the six retaining screws, but thanks for checking

* I am talking about removing the entire mirror cell assembly from the tube

* I have turned blue in the face trying to pull/twist the assembly free, but it hasn't budged even half a millimetre

[Paul M]

Make me think it's been bonded in for some reason.

As noted already, once those retaining screws are removed gravity will do the rest if care isn't taken.

My 250PDS mirror cell takes zero effort to remove and needs holding in place when the last screw is removed.

As an aside. When I removed my mirror  from its cell for cleaning some of the clip screws sheared as they were thread locked. And on reassembly i had a pinched mirror even when the clips were so loose I got mirror flop. I ended up binning the clips and bonding the mirror to the cell with silicone sealant.  Been great since!

[CraigT82]

On my old 200p the first time I took the mirror cell out I had to use a large flat bladed screwdriver as a drift and tap it out with a mallet as it was really stuck in there.   There was just enough of a lip where the cell meets the tube to get the screwdriver onto.  After that first time it got easier. 

[astronymonkey]

Hmm, I'm thinking this may need  a hairdryer on the outside tube to warm it up and expand it a little. It sounds like a bit of bonding so the expansion may help.

Cheers

[pipnina]

Hmm. Usually I find getting the cell back IN to be the hard part!

As an apprentice mechanic I can agree with Craig that tapping something against the outside lip of the cell might help to persuade it to move.

[Spile]

I used a thin screwdriver and carefully inserted it between the white tube and mirror mount. I then turned the screwdriver to prise the mount out. It certainly did not come out due to gravity. 

[malc-c]

13 hours ago, Spile said:

I used a thin screwdriver and carefully inserted it between the white tube and mirror mount. I then turned the screwdriver to prise the mount out. It certainly did not come out due to gravity. 

Is this a SW Explorer 200P on a EQ mount or a Dob version.  I ask that because Skywatcher have not produced the Explorer in a white tube for several years which might explain the reluctance for the mirror cell to detach itself from the tube 

[Spile]

Skywatcher 200P. Images on the link I posted.