Mirror in a 130m

[Ed the Fox]

Hi folks. Just asking for your help and advice on a skywatcher 130m I just purchased off ebay. 

I want to remove the primary mirror to place a center spot on it to make it easier to collimate. Having read some of the posts in here it would seem that taking the whole assembly out using the screws surrounding the tube is a no go, so I was wondering how removing the 3 retaining screws at the back of the tube then removes the mirror, seems that that will not work either (image 1).

The other thing is that the mirrors edge seems blemished in some way. I Have read that this is of no concern at the moment but could get worse (image 2)

Some answers please. 

Ed

[johninderby]

Just remove the screws around the bottom of the tube and remove.the whole mirror and cell. Thats the best way to remove the mirror.

From a bigger scope but the principle is the same.

 

Edited August 22, 2021 by johninderby

[AstroMuni]

On 22/08/2021 at 16:19, Ed the Fox said:

I want to remove the primary mirror to place a center spot on it to make it easier to collimate. Having read some of the posts in here it would seem that taking the whole assembly out using the screws surrounding the tube is a no go, so I was wondering how removing the 3 retaining screws at the back of the tube then removes the mirror, seems that that will not work either (image 1).

Take care that you dont loosen the wrong screws. One set helps align the mirror. Also make a note of the orientation of the mirror. I put a piece of tape on both back of the cell and the OTA to tell me which way the mirror was originally oriented.

[Gonariu]

Of course, the photograph of the mirror does not make us think well, is the instrument new or used? I have never bought anything from ebay, is there a possibility to make a return? Otherwise, if you keep it, I'm thinking that the mirror lighting needs to be redone. Here I leave the floor to the others.

Edited August 25, 2021 by Gonariu

[Alan64]

Your Sky-Watcher 130mm f/7 Newtonian, and with a spherical primary-mirror, has the exact same front cowling and rear primary-cell as my Celestron 127mm f/8 "Bird Jones"...

The primary-cell of our reflectors is quite and rather convoluted.  It's not as simply constructed as others.  If you remove these screws on the side round, the nuts on the inner side will fall off within the interior of the tube...

You'd have a very difficult time getting those nuts back in place.  Do not remove those.  Our reflectors are built like tanks, and are actually, seemingly constructed like one in addition.

You have no other option but to do this...

...and to remove three of the six screws, the ones screwed all the way down, and indicated in green within the following image.  You don't have to remove the locking screws which stand out a bit...

It just so happens that the three to be removed are the ones that are used to adjust the collimation, unfortunately.  They pass through the black, rubber grommets, indicated in red, which poorly act as springs, for tensioning.   You should remove only the mirror's staging platform, not the mirror-cell's frame, in that.

Whilst you have it apart, you can replace those black, rubber grommets with metal-springs.  The springs would make collimation O so much easier, you've no idea...

Within this thread, I have described and illustrated the aforementioned, and more besides, much more...

 

Edited August 25, 2021 by Alan64

[Ed the Fox]

Thanks for the replys guys, very informative. 

I would like to know where you get those springs from. 

[Alan64]

5 hours ago, Ed the Fox said:

Thanks for the replys guys, very informative. 

I would like to know where you get those springs from. 

I got my own from a local big-box hardware-lumber store, and out of this assortment pack...

I used the three of the four of stainless-steel from the pack...

I then cut them to length, to that deemed appropriate, with a Dremel rotary-tool and a diamond-encrusted wheel...

After that, I formed the cut ends to match the squared, uncut ends as much as possible, with pliers or other...

There are those ready-made, however those are for larger Newtonian-Dobsons.  They might work, depending on the scale.  They could be too strong for a 5" cell and mirror.  But I got that pack of springs for only US$5, and did it myself...

Edited August 26, 2021 by Alan64