How big can a conical mirror be?

[Moon (James)]

How big can a conical mirror be before it starts to deform under its own weight and you need to move to some type of floatation cell?

Mr. Royce offers them up to 16" - is that the limit?

Does anyone know how to do the maths or got some practial experience perhaps?

James

[David Fitz-Henr]

Hello James,
I asked Mark Suchting a similar question when I picked up my 12.5" conical mirror from him.

From memory there were a couple of issues to consider with conicals:
- The shape of the conical itself, in that you can design conicals with different edge thicknesses which affects their flexure. I believe that earlier conical mirrors may have had thicker edges, but of course that means heavier mirrors and is probably why they have trimmed them down.
- The difficulty of figuring a conical mirror due to flexure. Again from memory, I think that a 16" is near the limit of what can be achieved with current conical blanks (with some difficulty). I think that this may have been more the determining factor rather than the flexure in the actual mounting and use of the conical mirror in a telescope.

Mark, please jump in if I have gotten anything wroing here ...