Re: [ATM] Epoxy mirrors (again)

["Wayne Young" <atm@ganimede.demon.co.uk>]

> A mix of my names: "Shanti."  Interesting, but please call me Shane.  ;-)

Shane !  I am so sorry. My only excuse was that it was late at night (more 
like early morning) and I must have had a sleep-deprivation induced 
brain-fart.

> Have you been able to accurately measure the thickness from one attempt to 
> another?

Yes - sort of. So far, I've been wrapping tape around the edge of a flat 
substrate leaving a 1 mm "lip" and then pouring the resin into the shallow 
dish thus formed. When I remove the tape, you can see the layer of resin 
sitting on top of the substrate and I think I've got a pretty consistent 
layer thickness. I go to great pains to get the substrate absolutely level 
before I pour the resin. Just visually looking at the layer, I'd say I'm 
getting less than 100 um variation from one side to the other just due to 
the "slope" of the substrate.

In the future, I want to make the lip part of the actual substate. Wrapping 
tape is not very controllable !

> A convex meniscus will allow the low viscosity resin you are using to flow 
> right off the edge of your mandrel, wouldn't it?  How would you keep it on 
> there and consistent in thickness across the entire surface?

Yes - that is a concern. I was thinking of maybe coating the dam / lip at 
the edge of the substrate with a substance the epoxy doesn't like - a 
"resin-phobic" substance. I haven't the first clue what that might be though 
....

BTW - are attachements allowed on this list ? I could send some pictures of 
the ripples, if anyone's interested.

Wayne



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