Please Help - What Caliper Calibration Range is Acceptable for 1mm Measurements?

A set of calipers is calibrated from 8 – 150mm and yet the manufacturing line is checking parts under 1mm. How do I explain to the personnel that this is not acceptable? Is it not acceptable? Is this not the appropriate equipment? Or is it OK to calibrate the calipers outside the acceptable range? Is this range or precision or which term?

I'm not familiar enough with the vocabulary to know if I'm using the correct terms, so please by all means correct me with the more appropriate ones.

Please help!

Izoyd said:

A set of calipers is calibrated from 8 – 150mm and yet the manufacturing line is checking parts under 1mm. How do I explain to the personnel that this is not acceptable? Is it not acceptable? Is this not the appropriate equipment? Or is it OK to calibrate the calipers outside the acceptable range? Is this range or precision or which term?

I'm not familiar enough with the vocabulary to know if I'm using the correct terms, so please by all means correct me with the more appropriate ones.

Please help!

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It's kind of weird that the range is 8-150mm since the range usually starts from zero. Are they special in some way that they start from 8?

ScottK said:

It's kind of weird that the range is 8-150mm since the range usually starts from zero. Are they special in some way that they start from 8?

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are they inside groove calipers? They can start at 8mm.... if that's the case then the operator should only ever be using them for inside measurements. If they are improvising a zero point then using the jaws to measure an outside dimension of something they are not being used correctly.

ScottK said:

are they inside groove calipers? They can start at 8mm.... if that's the case then the operator should only ever be using them for inside measurements. If they are improvising a zero point then using the jaws to measure an outside dimension of something they are not being used correctly.

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Does he mean the Calipers themselves are verified between 8mm-150mm? I assume they're 0-150mm but when verified no value between 0-8mm is actually checked

Dazzur said:

Does he mean the Calipers themselves are verified between 8mm-150mm? I assume they're 0-150mm but when verified no value between 0-8mm is actually checked

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I've used inside calipers that start at something other than zero. You usually set them the with a ring gauge. like so:


When the jaws are closed the blades should be at 8mm. But the jaws overlap, they don't close together so you can't use them like regular calipers.

They are used for measurements under 1mm, but when they are calibrated, the smallest verification is at 8mm. I hope this better explains?

Dazzur said:

Does he mean the Calipers themselves are verified between 8mm-150mm? I assume they're 0-150mm but when verified no value between 0-8mm is actually checked

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They are used for measurements under 1mm, but when they're calibrated, the smallest verification is at 8mm. I think you understood what I was saying....should they be using these calipers for measurements under 1mm if that's the case? Thx

Izoyd said:

They are used for measurements under 1mm, but when they are calibrated, the smallest verification is at 8mm. I hope this better explains?

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I thought so. I can't give you an answer in terms of metrology.

Interesting question, ISO 9001 Clause 8.5.1 b) says the following:

b) the availability and use of suitable monitoring and measuring resources;

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Key word here being suitable, if you're measuring under 1mm I assume your Vernier has a resolution of at least 0.01mm, however you have no evidence of the accuracy of readings under 8mm.

I'm not sure on an exact answer to your question, but I'd defintley consider the way you internally verify or externally calibrate these. Is there not simply a way for you to verify these between 0-8mm? Do you have access to a single slip gauge / Jo-block? Buying them individually is extremely cheap.

I'm in the UK, but here's an example
(broken link removed)

I really appreciate Dazzur's help; however, can someone give me additional metrology assistance?

Most calibration procedures that I have seen recommend performing the calibration at 3 - 5 locations throughout the working range of the caliper. Some leave it open as to where those points are located, but some do specify that 3 locations should be spaced at the minimum, midrange and maximum of the range. For 5 locations, the additional two should be at 25% and 75% of the range. Doing this and using the results in a Linearity study should address your concerns.