Re: [ATM] Dog biscuit ripple -Bad?

[Ken Hunter <atm_ken_hunter@yahoo.com>]

It's a start but nowhere near finished. If I had that
surface, I'd start over by going back to a sphere and
use slower more managed strokes, less weight and sneak
up on the parabolic curve. It's better to not force
the glass, you have to "finesse" it.

Ken Hunter

--- dave g <omegacent@yahoo.com> wrote:

> G'day Everybody,
>  
> I'm making a 10inch f6 and I have just about got the
> paraboloid correction right as the numbers
> repeatedly come out very good but I'm little worried
> about the dog biscuit ripple.   Please look at the
> image at this link...
>
http://users.tpg.com.au/users/daveg/10inchf6_050626.jpg
> 
> Now, there appears to be some wide and shallow
> grooves running from 1 to 7 o'clock and 11 to 5
> o'clock but these don't rotate with the mirror so I
> guess they are an artifact of the camera (wife's's
> digicam) or something.  Also there is another effect
> at 9 o'clock that is due to a nearby wall.
> 
> I'm considering remaking my pitch tool and going
> back to a sphere and reparaboloize but before I
> destroy the current figure, I'd appreciate comments
> from you Learned Gentlemen and Ladies on the
> severity or otherwise of the mottled dog biscuit
> surface.
>  
> TIA
>  
> Regards
> Dave
> AUSTRALIA
> 
> 
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