Hi Rusty2
Thinking about your problems and understand your reasoning in regards to finding the mechanical axis of your SCT in hope of collimating the telescope, there are issues with regards to this. Laser out of alignment (can happen), visual back (focuser) not being square to the optical axis can lead to the belief that the mechanical axis is out of alignment and therefore collimation. What we should be looking at is the optical axis. It is true to say that the factory does align the mechanics along the mechanical axis and then collimate the telescope but collimation does not last due to rough shipping and other factors. Plus people who sell these telescopes must up their sales pitch with explanation about how to collimate and maintain these instruments.
So, anyway looking at the image of the correct plate in your first post, all the cork shims are in place and the telescope index is aligned correctly (white out paint on the corrector and tube). Important if you plan to remove the corrector ensure it is returned to the index mark, this was set in the factory.
Not knowing the history of the telescope e.g. new or second hand, this a good indication that the telescope is still in original factory condition other the then any tinkering with the collimation screws. I can assure you that the optic are correct so you are good there.
Been brushing up on my understanding of SCT optic but couldn’t find any info in layman terms to best describe them so I will let that hang for another time.
So collimation of an SCT is about aligning the optical axis with the centre of FOV. So for example if you are just going to do visual work then the collimation would include everything in the optical train e.g. focuser, star diagonal. Astrophotographer would be straight through.
As we want to align the optical axis we don’t need to worry about anything else, only need to ensure the star in the centre of FOV and the diffraction pattern is concentric. Keep this in mind collimation should be conducted on a star for best results. In my previous post I tried to explain this but I found that Celestron gives a good example on the support page including pictures, see link
https://www.celestron.com/blogs/know...limation-guide
If you can, perform this task during the day with and artificial star, it will give you time to examine your work and ensure you are on track and also zero out any frustration. When you are spot on and have a nice Airy Disk with the artificial star, then finalise your collimation on a real star, about 4th mag.
Once you have collimation and still want to use a laser to check. Place the laser in the back of the scope and mark the return beam with a dot. Only work if you have a 45degree opening on the laser.
Any real feel your pain and I hope the information I provided will help get you telescope into tip top shape.
Hang in there, Cheers
Anthony.