How do I calculate Correction to Caliper Calibration Data

[bearvn]

Hi all,
My caliper have been calibrated and the results as following:

Reference value: 10,00mm -> error:-0.01mm
Reference value: 25,00mm -> error: 0 mm
Reference value: 50,00mm -> error: 0 mm
Reference value: 75,00mm -> error:-0.01mm
Reference value: 120,00mm -> error:-0.01mm
Reference value: 170,00mm -> error:-0.01mm
Reference value: 270,00mm -> error:-0.01mm
​

I use this caliper to measure dimension of an object, for e.g reading value is 35.01mm, does this reading need correction? If so, how do I calculate this correction because the reading is not the same as value shown in Calibration Certificate? I'm looking forward to your advice.

 

[Ninja]

Need some more info, bearvn.
You give accuracy data, but not perspective.

How accurate does the tool need to be in the application? Is your spec 35mm +/- 2mm? If so, don't worry wbout it (but keep a record of it). IF it's 35mm +/- 0.01mm, something must be done.

What about repeatability? Is the caliper consistently off by the same amplitude and the same direction?

A tool is just a tool...the question isn't just the error (though that is certainly included), it's how the error compares to the needs of the process.

 

[mdurivage]

I would have to ask if this is the correct measuring device for your application. .01mm is .0004". If you are worried about .0004" I would suggest that you use a micrometer.

 

[bearvn]

Need some more info, bearvn.
You give accuracy data, but not perspective.

How accurate does the tool need to be in the application? Is your spec 35mm +/- 2mm? If so, don't worry wbout it (but keep a record of it). IF it's 35mm +/- 0.01mm, something must be done.

What about repeatability? Is the caliper consistently off by the same amplitude and the same direction?

A tool is just a tool...the question isn't just the error (though that is certainly included), it's how the error compares to the needs of the process.

It's 35mm +/- 0.1mm. So, it doesn't need a correction, isn't it? Your reply is so much helpful. Thank you.

 

[Ninja]

Well now, your error is 10% of your specifications range. That's pretty significant, no?

I would tend to agree with mdurivage and wonder if you are using the right tool for the job. Calipers for measuring 35 +/- 0.1mm would make me a bit nervous, but then it is on the outside edge of my personal experience so take it as it is.

Either way, accepting a 10% error in the gage accuracy vs. the spec range is somewhat questionable.

Have you performed an Anova Gage R&R on your testing? Have you by this method shown that your caliper method is indeed a valid tool for measuring this part to this tolerance?

Just thinking out loud.