Re: [ATM] Conical mirror for Newtonian

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

andrewstuartallen@andrewallenweb.com wrote:
> I'm considering making a 12.5" f/6 mirror for a Newtonian using one
> of the conical cross-section blanks available from Newport Glass
> (see http://www.newportglass.com/angwcat.htm).  The Royce Optics
> web site (http://www.rfroyce.com/conical/) advocates conical
> mirrors for Newtonians, but I wonder whether there are issues with
> supporting those thin edges while working on the mirror, or
> possibly other things to watch out for?
> 
> Can anyone relate experiences or give advice on this? Thanks!

I haven't worked one, but a carpet-lined support made of plaster or 
something else that sort of matches the shape of the back of the 
mirror might be good enough.  That should definitely get you through 
fine grinding.

If you polish and figure mirror-on-top with a full-size lap, then the 
problem disappears.  You shouldn't need a subdiameter lap for a 12.5" 
F/6 anyway.

I suspect if the support is of only decent quality you would have no 
problems working tool-on-top since those blanks won't flex that much. 
  (Remember, the mirror cell is just a post!)  But you will lose 
polishing slurry through the hole in the middle working TOT, so MOT 
may be more convenient.

	Mike Lockwood

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