Re: [ATM] 20" FS update and what size grinding tool

[Ric Rokosz <radicell2@yahoo.com>]

6 Thanks for the procedure Richard!
> 
> So, what size grinding tool to make?
> 
> I am in general an advocate of full size tools for
> ginding mirrors, but, when you are dealing with a
> 20"
> mirror, the thought of having to hump around a full
> size tool, causes me some concerns. 
> 
> The question is, how hard will it be to keep an
> uniformly spherical surface with a smaller tool.
> 
> 12" would be nice, but effective?
> 16" I would hope I could keep spherical with it, and
> not have to go to a 20" tool.
> 
> Then there is the question of how thick to make the
> grinding tool.


Dental stone and hydrastone are really stiff materials
when dried slowly.Have done a 24 incher f/3.3 with a
full diameter hydrastone tool only 3/4 inch thick at
the edge with small tiles fiberglassed onto the
surface.The lighter weight allowed manual use of the
tool - the only heavy part is moving the tool on/off
the mirror.Once wet with grit the too moved easily.

Ric


       
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