"Peter H." wrote:

Diamond cutting has been used far before the "early 1970s", more particularly
in the production of precision rotating magnetic media, used in what are now
called hard disk drives, but were originally called direct access storage
devices (DASD).

It is "prior art" ... by several decades.

Ex-Cello Corp made the diamond cutting machines which IBM used since the 1950s
for this purpose.

Peter,

It may be worth noting here that the diamond cutting referred to, is
more like the flashy cuts applied to jewellery, rather than cutting
"with" diamond or diamonds.

Cheers
Trevor Jones