[ATM] newbie question

[Nigel Weeks <nweeks@prism9.com>]

 I've had a bit of a search through the archives for this list, but
can't find any threads or comments, but I apologise if it's been asked
before.  
 What are the pros and cons with making a primary paraboloid mirror
purely out of aluminium?  

 I can see it's softness making it easy to machine, shape, scratch,
and repair.  

 I can see it's thermal conductivity enabling it to reach ambient
temperature very quickly, as well has heating from your hands when
shaping it, possibly causing errors during grinding and finishing,
requring a jug to prevent hand contact transferring heat.
 I can see it's light weight being beneficial to the portability of
scopes, especially if additional material is removed from the back of
the mirror prior to grinding and shaping, so the back of the mirror
has a honey-comb appearance.  

 Being an alloy, you could tap threads straight into the back for
mounting and adjustment if needed.  

 Aluminium is a popular optic  mirror coating, so all the
alloy
mirror needs is the protective coating after polishing  

 It's tendency to oxidise may be a drawback, but the protective
coating will handle this.  
 Over to the gurus! I'm about to go buy 2x 18"x2" chunks of alloy,
one for tool, one for mirror, and start grinding.  

 Someone talk me out of it...  
 Nige   
 Nigel Weeks  

 Software Engineering
 Prism9 Industries
 email: nweeks@prism9.com    
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