On 21 Aug 2003 20:07:34 GMT, a (Dave Baker) wrote:

Subject: Early surface plates: How were they made?
From: (Chris Lindquist)
Date: 21/08/03 20:43 GMT Daylight Time
Message-id:

I've been trying to find out exactly what process was used for
originating a surface plate in the good old days. I expect it involved
careful hands and a large amount of scraping, but what provided a
reference for "flat"? And how flat was flat around the turn of the
century?

I'm not planning to try this at home, of course. My Chinese granite
plate is plenty flat enough, thanks. But I've been going through my
books looking for an answer to this chicken-and-egg question without
finding a solution.

Can anyone help?

By lapping 3 plates against each other with grinding paste until all three are
flat. The same way as reference plates are made now. The ancients could make a
plate as flat as we can now. The technique requires no special technology.

Yes, in fact a quartz (?) sphere (12" diameter) was hand made by the
chinese I believe over 1000 years ago and is very nearly perfect.
It's in the Smithsoanian. Very interesting to imagine how the did it.

John

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