Removing primary mirror from 130M

[soldave]

So I'm thinking I should centre dot the primary mirror of my 130M to make collimation with a cap easier. I've seen a few guides such as the one at https://garyseronik.com/centre-dotting-your-scopes-primary-mirror/ once the primary is off the scope, but I've got to get it off to start with. Now there are some screws around the side, but these go into inside the scope, and looking down it that's going to be a pain to say the very least. Now the base of the primary mirror has 6 screws; three adjusters and three locking screws. Would I be right in thinking that if I remove all locking screws then the primary mirror and base would just come off the back of the scope? The plastic base could very well be in two parts from what I can see so I think it's possible, but wanted to get thoughts from people as it must have been done by othes.

The alternative would be to just get a Cheshire, as I don't believe I'd need a centre dot for that.

[Cornelius Varley]

10 hours ago, soldave said:

Would I be right in thinking that if I remove all locking screws then the primary mirror and base would just come off the back of the scope?

No, you wouldn't be right. The collimation and locking screws should not be removed. The screws you need to remove are the ones around the side of the tubes. These are usually self-tapping screws or have captive nuts. Once these are removed the rear will come off.

[soldave]

I think the issue is that, looking at other people's experiences, the nuts aren't captive. Meaning you need a combination of gorilla-like arms and long needle-nosed pliers to hold them in place whilst you try to tighten the screws, neither of which I posess!

Source: 

 

[wookie1965]

Use insulation tape to reorientate the mirror cell with the tube. I. E put insulation tape on the tube and the cell at the same place. 

 

Edited February 23, 2020 by wookie1965

[soldave]

15 minutes ago, wookie1965 said:

Use insulation tape to reorientate the mirror cell with the tube. I. E put insulation tape on the tube and the cell at the same place. 

 

The alignment I don't think I have an issue with, and have seen that mentioned before. The issue is with the non-captive nuts on the inside of the tube, their positioning in relation to the primary platform, and how I'd get it all back together once removed. This is assuming the nuts are not captive, which is what I've heard from the 130M. May be incorrect, but I can't get a good enough eye on them from the other end of the tube.

[DaveL59]

the orientation of the mirror cell relative to the tube is important, since if you replace it in a different orientation you will find the collimation is out, possibly by a fair margin. If you replace it in the original orientation you may need to a slight tweak but not much more.

I don't have the 130M but the older 130EQ2 long tube, had no issue removing the mirror cell, but for sure work with the tube on its side just in case. At least if any nut does come loose and drop it'll not land on the mirror.

[soldave]

1 minute ago, DaveL59 said:

the orientation of the mirror cell relative to the tube is important, since if you replace it in a different orientation you will find the collimation is out, possibly by a fair margin. If you replace it in the original orientation you may need to a slight tweak but not much more.

I don't have the 130M but the older 130EQ2 long tube, had no issue removing the mirror cell, but for sure work with the tube on its side just in case. At least if any nut does come loose and drop it'll not land on the mirror.

On yours, were the nuts in the tube captive?

[DaveL59]

believe so, tis a bit of a long tube to see clearly without removing the mirror cell but the ones further up are so I assume same for those. Just don't overtighten when you refit so you don't risk breaking them away.

[John]

Here is a web page describing some other modifications to the Skywatcher 130m which has some photos and diagrams of the primary mirror cell including the attachment to the tube. These suggest non-captive nuts on the screws that hold the cell to the tube:

http://astrobeano.blogspot.com/2013/04/moving-mirror-on-skywatcher-130m.html

Also here is a thread from a while ago on someone wanting to remove the primary mirror for the same reason that you do. Skywatcher have not made it an easy task !:

 

[DaveL59]

oh, that doesn't sound like fun then  

[soldave]

3 minutes ago, John said:

Here is a web page describing some other modifications to the Skywatcher 130m which has some photos and diagrams of the primary mirror cell including the attachment ot the tube. These suggest non-captive nuts on the screws that hold the cell to the tube:

http://astrobeano.blogspot.com/2013/04/moving-mirror-on-skywatcher-130m.html

Also here is a thread from a while ago on someone wanting to remove the primary mirror for the same reason that you do. Skywatcher have not made it an easy task !:

 

Thanks. That second link was the thread I read was what got me worried initially about the nuts. Looks a right pain so I'm thinking maybe a Cheshire would be the way to go.