Re: [ATM] 12.5 inches BVC mirror polishing and figuring difficulties

["Mel Bartels" <mbartels@bbastrodesigns.com>]

> Please take a look at my BVC 12.5 in. F/4.8 mirror : 
> http://www.axeinformatique.com/temp/Mirror/BVC_Mirror.html
> and please advise me if I should :
> 1- Sell the thing to a more experienced polisher, and buy a completed 
> mirror (It's my first mirror).
> 2- Persevere and do what ? How much energy still needed ?

The figure looks quite fine - at least smooth enough to attempt 
parabolization from.  Sure, there's a little turned edge and a center 
problem, but those are very minor, compared to the amount of parabolization 
that the mirror requires.

Certainly you must keep in mind that, if you do the same strokes et al, then 
you will get the same results.  So the fact that the profile is not changing 
is actually a good sign that you are consistent.

The difference in the lap color in the center of the lap is concerning 
though.  You definitely do not want pitch of a different melting point and 
viscosity in the center vs edge of the lap.

So, is the mirror fully polished out?  If so, are you ready 
(psychologically) to begin parabolization?

If so, then you will likely need to deform your lap, or make a smaller 6 
inch (15cm) lap, or use extremely aggressive wide long strokes.

Mel Bartels 

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