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Date:         Wed, 15 Dec 1999 21:25:00 -0800
Reply-To:     Austin <austins@IX.NETCOM.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Austin <austins@IX.NETCOM.COM>
Subject:      Re: metric vs. English
In-Reply-To:  <4.2.2.19991215205622.070b9390@127.0.0.1>
Content-Type: text/plain; charset="us-ascii"

At 08:59 PM 12/15/1999 -0500, you wrote: >At 19:03 12/14/99 , t obrien wrote: >>>The silliest thing of all is that the US still does not use metric. >>Excusse meee.... >>We do use metric... > >It's been pointed out that .001 inch is about the limit of machining >accuracy, and .0001 inch is about the limit of grinding accuracy -- this >makes inches a very convenient unit in the machinist's world. Millimeters >are much less convenient in this instance. > >David Beierl - Providence, RI

Most CNC machine tools are built as metric machines, w/ inches & required algorithms thrown into the software, & the smallest increment that is programmable is .0001 inches (one tenth of one thousandth of an inch): however the machines will accept .001 mm as a metric least increment, which works out to ~.00004 inches, or 4 tenths of 1 tenth of a thousandth of an inch!! i.e., in metric mode the tools are more than twice as accurate!

FWIW: a human hair measures ~.003" in diameter - 3 one-thousandths of an inch. There exists a penultimate unit of measure that made it's way down from NACA in the old days known as RCH - ostensibly the finest unit of measure ever detected, but which I can't divulge in a public/family forum (let yer polluted imaginations run wild, & the context is that in the old Apollo days it was definitely a man's world, that going into space business!).

Austin


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