Re: [ATM] Fringe testing Dall Kirkham secondary

["Rod Brackenridge" <rjbr@lycos.com>]

> 2.5 waves is not a lot to polish off of a small mirror (but it's 2.5 
> waves at the edge, so this will take longer than if it were that much 
> too high in the center).
> 
> How large is the secondary?
> 
> If the curve changes very slowly, you may need to use a more 
> aggressive polishing stroke.  Be careful not to turn the edge.  Press 
> often, or the pitch may resist the change in curvature, depending on 
> the hardness.  Hard pitch will likely not work so well here.
> 
> Pressing in a petal lap is another option.  Once it is close, press 
> the petals away and spherize and tweak.
> 
> Good luck.
> 
> 	Mike Lockwood


The secondary is 100mm diameter, although the design requires only about 84mm - which I guess negates my fear about turning the edge.  I intend to mount a short cylendrical front baffle about the same diameter as the blank.

You and Bob have convinced me to try the longer strokes.  If that does not work, I'll try a softer lap.  The one I am using is quite hard.

Thanks again,

Rod.
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