12" GSO mirror removal and re-mounting
Posted 18 November 2012 - 07:33 AM
After it's out, how do I re-mount it? In silicone again or is there a better way. Is there any sort of aligning it in the mount?
Posted 18 November 2012 - 09:09 AM
We used cork on the mirror of the club's 16" Lightbridge when we re-installed it. On the bottom with some also on the sides for a snug - not tight fit. We allowed for a bit of expansion between the mirror and the clips.
Posted 18 November 2012 - 09:53 PM
Posted 23 November 2012 - 02:14 PM
Posted 23 November 2012 - 06:43 PM
While your mirror is away, why not modify your cell to use edge clips and side supports that are guaranteed to avoid the problems mentioned above? Maybe your cell already has these and GSO just added glue for good measure? If you show us a picture we can better suggest how to proceed.
Posted 23 November 2012 - 07:01 PM
Posted 23 November 2012 - 07:36 PM
Posted 23 November 2012 - 07:45 PM
Please forgive all the questions as this is all new to me.
Posted 23 November 2012 - 08:12 PM
If your clips squeeze down on the mirror this is not a good thing at all. It can cause warping and astigmatism. Maybe you could add spacers between the two parts of each clip to allow tightening without squeezing?
Posted 23 November 2012 - 08:33 PM
Posted 24 November 2012 - 08:21 AM
Note that the page also mentions the ability to glue mirrors that are full thickness up to about 15". Full thickness in your case would be ~2" thick, and I'm pretty sure that the GSO mirrors are somewhat less than this. A floating support is really best.
Another way to make the edge supports is to drill and tap holes for nylon bolts. This approach provides some tightness adjustment, and is useful for mirrors that are mounted equatorially. However, in your case the edge supports doing all the work will be at 7:30 and 4:30. You can simply glue a couple shims at those positions--just be sure you use something the right thickness to maintain proper mirror centering. There will not be any pressure on the other two supports while using the cell in a dobsonian mount.
One last point--Make sure that the pads used on the triangles are not sticky or uneven. You might want to replace them with new felt furniture pads if they are.
Posted 24 November 2012 - 09:57 AM
Sorry for all the question but this is all new to me.
Posted 24 November 2012 - 10:03 AM
Posted 24 November 2012 - 12:08 PM
If I want to go with the tapping and screws, would a 1/4" screw be enough? Just one NYLON screw per position? Is exact positioning important or is close enough good.
I do appreciate all this info. I feel I'm now in the position to do any mods needed while my mirror is out to Majestic.
Posted 24 November 2012 - 12:26 PM
The bolts (one at each position) should be placed at the mirror edge center of gravity, which is very close the midpoint of the edge--just a tiny bit shifted towards the rear. The edge calculator gives you the numbers. For a mirror as thick as yours the tolerances are not very tight.
Looking again at your cell, it does not appear that there is a lot of clearance between the mirror and the inside rim. Your bolts will only protrude a short distance. You still need to be sure that the mirror clips will prevent the mirror from falling out.
Posted 24 November 2012 - 02:01 PM
Posted 24 November 2012 - 03:27 PM
I have been using this method for three years now with great success. It holds the mirror gently, and still allows expansion & contraction when necessary.
Posted 25 November 2012 - 01:43 PM
Posted 25 November 2012 - 03:35 PM
Posted 29 November 2012 - 09:55 PM
Speaking of my Mirrors, I talked to Jeff at "Majestic Coatings" today. I can't believe my mirrors arrived Monday and were shipped back out on Wednesday!!!! I"ve heard nothing but good about him and now I can attest to it myself!!!
When it gets here, I have the center mark to install (Catseye). Again, Kudos to another vendor, Jim Fly at Catseye talked to me and explained his opinion on what I needed and didn't treat me like the idiot I felt like. Even after I ordered and changed my mind, he went out of his way to accommodate me.
Anyways, I'll post up a couple of pics as I finish up my project and hope I'm not being a pain but I've never really worked on anything like this. I know I couldn't be doing this without everyone here's input.
Posted 30 November 2012 - 08:54 AM
Posted 01 December 2012 - 04:26 AM