"Anthony" wrote in message
...
"Harold and Susan Vordos" wrote in
. net:

While it may be a bit of a stretch for you to come to terms with what
I'm about to say, when I was grinding I could measure with a tenths
mic and hit the size, *reliably*, within .000050". We had a
Sheffield shadowgraph at our disposal, which verified our readings.
Probably not very impressive in today's world, but a Sheffield was
cutting edge when I was in the shop.

While it _can_ be done, I fail to agree that it can be done reliably over
the long haul. You may be able to do it repeatably, but the day you are
out on vacation, Bob your coworker most likely won't be able to repeat
your success.

As I've already stated, that's what separates those that can from those that
think they can. Those of us that were successful kept our jobs. Not all
did.


By today's quality standards, a gauge must have a resolution a minimum of
10x finer than the tolerance you are measuring. It _must_ long-form R & R
(Range & Repeatability) at less than 20% of your tolerance for general
work, and most all precision component customers require R & R of 10% or
less.
All of our work falls into the latter 10% category.

I'm not convinced anything has changed where any of that is concerned. It
was common knowledge that tools had to be built with 1/10 tolerance as
compared to the parts for which they were created.


A long form R & R requires the range and repeatability of the gauge to be
measured, including the human factor, cumulatively all the way back to
the NIST standard.

Univac was certified accordingly. While it was not my area of expertise, I
rubbed shoulders with them on a regular basis. It was required that all
measuring instruments in the plant (including personal tools) be certified
monthly. They banded each tool with a given color, designating the last
certification.


It's a fairly easy task for a +/-0.001" tolerance, it's an entirely
different story for +/-0.00005" tolerance.

I thought I said that! :-)

As an operator of grinding equipment, all it took to get on my bad side was
to walk up to the machine and lean on it. That was strictly forbidden, but
few understood the ramifications. I'm sure you must enforce similar, if
not identical, restrictions.

Harold