RE: [gingery_machines] Re: new article: How Accurate is Your Micrometer?

 

Dave,

Both of these articles are very good. No reason to duplicate any of the
text. I just included the URLs in my article along with an additional
acknowledgment.

You say "stacking gage blocks to achieve an accurate dimension for testing
will also give incorrect results". I'm not sure what you mean by
"incorrect". The entire point of having gage blocks is so you can stack
them. I do understand that each block contributes an uncertainty to the
total. By knowing the total uncertainty, I can judge how much to trust the
testing result.

I was just playing around with my spacer blocks and my HF caliper. After
zeroing, I took out a 1.000" spacer and the caliper read 1.000". I then took
out a 0.5000" spacer and the caliper read 0.5000". I know that the caliper
only reads 0 or 1/2 thou in the right most digit. So I conclude that within
the displayed value on the caliper, it is damn good at 0.5000" and 1.000". I
won't venture a guess as to the accuracy at any other values.

These calipers don't have a threaded rod and threaded sleeve but they do
have a pattern on the body and a pattern on the pick up so I expect have
similar error sources.

Rick

-----Original Message-----
From: gingery_machines@yahoogroups.com
[mailto:gingery_machines@yahoogroups.com] On Behalf Of Dave
Sent: Monday, January 24, 2011 4:50 PM
To: gingery_machines@yahoogroups.com
Subject: [gingery_machines] Re: new article: How Accurate is Your
Micrometer?

Rick this might help on your article
http://www.starrett.com/download/222_p1_5.pdf
http://www.angrave.com/catalog/GageBlocks.html
but testing the accuracy of any measuring tool in an uncontrolled area will
give you incorrect results. stacking gage blocks to achive an accurate
dimension for testing will also give incorrect results. Gage blocks have a
+/- tolerance, although small will effect the measurment in an uncontrolled
enviroment.
For the average hobbist +/- .001 is close enough, and doesn't need to worry
about the accuracy of the tool , just the repeatability.

Dave

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