I am aware of some of the nice things that could be done IF the internal and
external jaws were exactly the same.
But the original task was "measure the bore so piston rings can be ordered"
and I still believe that "find something to set a known zero datum and then
have at it" was a reasonable procedure for that task and did not require that
the jaws be exactly the same.
By the way, what are you using for you "standard" for inside measurements? I
can see how gage blocks would be used for determining the accuracy of outside
and depth measuring tools but do not see a way to use them for testing the
accuracy of inside measuring tools. Several kludges come to mind but I though
I would as someone with more experience than I.
Arvid
----- Original Message -----
From: David Scheidt
To: Arvid Jedlicka
Cc: shop-talk
Sent: Monday, November 02, 2009 12:26 PM
Subject: Re: [Shop-talk] Micrometers
On Mon, Nov 2, 2009 at 9:49 AM, Arvid Jedlicka <arvidj@visi.com> wrote:
We will agree to disagree on the "is junk" part.
And I believe I did think about it. I came to the "accurate measurements
party" pretty late and therefore everything I have is digital. A mechanical
vernier caliper may not have any way to set the zero datum but all of my
digital ones do. So I have naively set the zero as needed and gone about the
business of getting what appear to be accurate measurements - i.e. things fit
together when I am done - without any problems.
One of the things that I use calipers for is to transfer a measurement from
one part to another. I'll measure the size of a hole, and then use the
external jaws to mark a piece. I'd throw away any caliper that required me to
read the measurement, close the jaws, set the zero point, and then reopen the
jaws and set them to a particular measurement, which I'd've forgotten by this
point. The guy who taught me to do this (and also how to read a vernier
caliper) was a tool maker for decades; it's standard practice when making
things where absolute measures aren't important, just that things are the same
size.
--
David Scheidt
dmscheidt@gmail.com
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