Pimary mirror attachment
Posted 01 February 2013 - 11:20 PM
Posted 02 February 2013 - 07:15 AM
Can you post a picture of the cell? Is the mirror thickness 1.5"?
Posted 02 February 2013 - 02:39 PM
For larger primaries, say 16" and up you want to keep the primary free and floating on the cell support locations.
Posted 02 February 2013 - 05:12 PM
Posted 02 February 2013 - 05:18 PM
Trying to figure out how to post a pic of the cell.
Posted 02 February 2013 - 07:23 PM
People often say "I used silicon and it words fine". This is what is known as anecdotal evidence. A properly designed floatation cell has the strength of numerical analysis to ensure that it does what we want it to do.
To post a photo first resize it to less than 200 Kb. Then choose "preview reply" beneath the text box at the bottom of the page. When you are in preview reply select "browse", which will give you an opportunity to attach the picture. Then click on Ok, submit.
Posted 03 February 2013 - 02:40 PM
I agree that for larger mirrors "gluing" the mirror down could restrain the mirror. It may not be to grow or contract freely in the radial direction when needed because of small thermal expansion coefficient differences between it and the cell supports. I was not suggesting “gluing” large mirror down.
I would be interested in learning more about the effects of in-plane loadings on small mirrors and the resulting deflections. Is there a way to account for typical lateral supports used to restrain a mirror from sliding around in its cell? Are there papers or programs out there to analyze supports like straps, side bumpers, etc?
To-date my experience and that of those who helped me become an ATMer is that the very small differences in lateral expansion/contraction of “small” mirrors just get absorbed by the flexibility of the silicon blobs and other parts of the cell that just “give” a little.
I agree that this practice is not based on the “strength” of numbers, as you put it.
Surely the number of successful telescopes in use today that included a blob of silicon here or there to support a small primary or secondary mirror counts for something?
Posted 03 February 2013 - 03:13 PM
There is an excellent resource for comparing mirror edge supports that also talks about mirror gluing:
Mirror edge support calculator
Posted 03 February 2013 - 04:00 PM
Posted 04 February 2013 - 07:36 AM
Posted 04 February 2013 - 12:48 PM
Posted 04 February 2013 - 08:31 PM
I've used the Velcro strip on my 10" and that works well too. The velcro hangs on like grim death ( Industrial strength ) yet it can move that little bit to allow mirror expansion without any strain. I have edge brackets just in case, they don't touch the sides. My mirror has never moved.