Metrology Best Practices
Metrology Best Practices
(OP)
In my years as a metrologist, it has been my practice to report dimensions to 1 place further than the specs given on the print that I'm working with. I know that I have seen this practice in writing as a "best" practice. My boss, who does not understand metrology, wants me to start reporting to the number of decimal places shown on the print. Can anybody provide a link to, or a direct quote from a source specifying this "best" practice?





RE: Metrology Best Practices
I am not aware of a procedure that defines all of this. If it were me inspecting, I would report the number of decimals I had confidence in.
If you are doing metric drawings to ASME Y14.5M-1994, the trailing zeros are supposed to be deleted from the drawing dimensions, making your problem moot.
JHG
RE: Metrology Best Practices
Thanks.
RE: Metrology Best Practices
KENAT, probably the least qualified checker you'll ever meet...
RE: Metrology Best Practices
However, that is not a hard rule. What you really need to concentrate on is the reporting of SIGNIFICANT digits per ASTM E 29 – 02. This means that you would "Round-up" data that is over 5 in the following decade. SUch as 2.3505 would be rounded-up to 2.351.
RE: Metrology Best Practices
Not sure if you use it but extra digits beyond what is specified are key to the whole process.
E.G. 2.3505 then 2.3504 then 2.3503 might indicate wear in a drill bit.
EG. # 2 – a set of solid 2.3505's would be good. If you see 2.3505, 2.3504.2.3506 it might indicate collet wear.
Tom
Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com
Good engineering starts with a Grainger Catalog.
RE: Metrology Best Practices
RE: Metrology Best Practices
I too used to use the rule of "10".
But have recently been told that a "rule of 4" ( four times more accurate ) can be applied to CMM results. Although this could lead to the measuring tool uncertainty actually using up 25% of your tolerance.
RE: Metrology Best Practices
the quote is from the thread "According to ANSI Y14.5M-1994 (and 1982), Paragraph 2.4 on page 25
"All limits are absolute. Dimensional limits, regardless of the number of decimal places, are used as if they were continued with zeros.
Examples:
12.2 means 12.20...0
12.0 means 12.00...0
12.01 means 12.010...0
To determine conformance within limits, the measured value is compared directly with the specified value and any deviation outside the specified limiting value signifies nonconformance with the limits."
"