"Mike Firth" wrote in message ...
There was a thread on here a while back on this topic after someone asked
about the same question and flat for that person turned out to be
EXTRAORDINARILY flat - like quite an area flat to 0.00001" or some such.
If you are talking about several square inches and flatness measured with
Newton rings - basically you use very fine grit with stuff that is basically
flat to start with and reverse the techniques of mirror grinding - instead
of using force on the edge revolved around to make the basic spherical
shape - you apply even force and use one pretty flat surface to take the
high points off another pretty flat surface.
Float glass is rather flat for the purposes of people who want to grind a
flat surface on steel cutting tools.

My experience with float glass is that it is noticeably wavy although
amazingly smooth.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit45.htm Latest notes
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"Allan Adler" wrote in message
...

I've only seen the skill of grinding glass discussed in the context
of grinding lenses. In particular, the glass is supposed to acquire
a curved surface as a result of one's efforts.

What if you want to grind a piece of glass so that it is instead perfectly
flat? Does this involve essentially different techniques, both in grinding
and in testing, or do they belong to a common context?

I realize nothing is perfect, so it is also necessary to ask how flat one
can expect hand ground glass to be?

There are lots of books on grinding lenses for telescopes. Where can one
read about how to hand grind glass perfectly flat?

Ignorantly,
Allan Adler



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