Re: [ATM] processing techniques for soft optical glass?

[Mark Cowan <toolontop@yahoo.com>]

Sounds reasonable to me, certainly not using water for overly soluble glasses
is a good idea.  Polishing those will be challenging though.  Salem
Distributing has some info in their grit/polish catalogs about exotics, IIRC. 
There are non-ceria materials intended for polishing plastics and the like.

Best,
Mark


--- David Weinshenker <daze39@earthlink.net> wrote:

> So I've been poking around in glass catalogs and running
> a few computer searches for good pairs and triplets
> (in terms of accurate "curve match" across the spectrum)...
> and it turns out that the glasses that tend to show up
> in the most desirable pairs - e.g., the interesting
> "fluoride" crowns and many of the "special dispersion"
> flints - seem to be rather soft, soluble glasses with
> low resistance to abrasion, moisture, and chemical
> attack.
> 
> ("Is that glass, or rock-salt?")
> 
> It occurs to me that trying to "hog out" the curve on
> a small lens (e.g. 2" diameter) of such glass (against
> a corresponding glass tool which was to be generated
> to the matching shape in the process) might work badly -
> too much of the soft lens glass might be ground away
> by the time the tool (of hardener "ordinary" glass)
> had the desired radius.
> 
> An alternative method that occurs to me would be to
> use two "plain" glass tools, oversize relative to the
> lens - say 4" diameter "boro" or "soda" glass disks
> for a 2" lens - the process would be to grind them
> against each other (with a suitable combination of
> the usual sort of radius-generating and smoothing
> strokes), progressively working them toward the
> target radius while alternately grinding the lens
> glass against the appropriate tool of the pair.
> 
> Each tool+tool grinding session would deepen the radius a bit
> and bring the tools to good spherical contact at that radius,
> and then the ssmaller lens would be ground against the tool
> (with a stroke designed to  equalize wear over the surface
> of the larger tool) until it was in full contact at the new
> radius.
> 
> Does this sound like it could work well? Would there be
> any virtue in using a fluid other than water for suspending
> the abrasive grains (perhaps a light mineral or fluorocarbon
> oil) which would have less of a solvent action on the glass?
> 
> -dave w
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