On 2010-08-07, Wes wrote:
"DoN. Nichols" wrote:

On 2010-08-04, Gunner Asch wrote:
http://inlandempire.craigslist.org/tls/1873615296.html

Hmm ... no mention of the standards, and the one opened box
shown does not have the standards present. For that price, I would
expect the standards, too.


What do you think your chances are of measuring something 17.75" to 0.0001"?

*With* standards -- and in a temperature controlled room with
good thermally insulating gloves for handling the micrometer and the
standard -- maybe.

Let's see -- steel is 11 to 13 E-6 per degree Celsius. So
17.75" would vary 0.000195" to 0.000231" (depending on alloy) per degree
C, or 0.000108" to 0.000128" per degree F, so the room would have to be
very well temperature controlled, and the parts, micrometer, and
standard allowed to "soak" at temperature for quite a while, given the
possible mas of a 17.75" part. I think that with that degree of
sensitivity, even the person performing the measurement would have to be
in a thermally insulated suit -- and perhaps to breathe through a hose
to the outside to minimize the effect of his/her breath on the
measurement.

No standards would indeed be a deal killer.

Certainly for me at that price. If the whole set were going for
say $200-$300 -- I might consider buying standards as I needed them, and
typically one standard for two adjacent size micrometers. (Hmm ...
probably a cheap Chinese set of gauge blocks or several (let's see, 6",
3", 2", 1" in the sets, that is 12" -- so two sets might do it.)

Enjoy,
DoN.

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