Micrometer and Vernier Caliper simple calibration process

Cats Clause

Starting to get Involved
#1
Hi all

My client, (a small UK engineering company manufacturing turned, not ground, components) are calibrating themselves their external micrometers (0-25mm) and vernier / digital calipers (0-150mm). To do this they are using a gauge block set which is calibrated externally to international standards by an approved laboratory.

My question is regarding observed permissible error on the types of equipment. At the moment the calibration work instruction states:

"Verniers are used to measure to an accuracy of 0.015”. Vernier calipers must be accurate to one hundredth of this figure i.e. 0.000150” (There is currently no stated figures for micrometers or digital calipers in the work instruction.)

This is a small company and not a high precision environment, so I am looking for a simple calibration procedure and most importantly realistic observable error figures permitted, when calibrating the three types of equipment please.

Thank you in advance.
 
Elsmar Forum Sponsor

Jim Wynne

Staff member
Admin
#2
The general expectation is 10:1, not 100:1. Perhaps descriptions are different in the UK than in the US, but this is a vernier caliper:

5146u8xU0NL._SX522_.jpg


You're probably using dial calipers (in addition to digital calipers).
 

Ron Rompen

Trusted Information Resource
#3
I agree with Jim. And I don't believe that there is a vernier caliper available that has a resolution of .00015". A more appropriate target would be ± 0.0015"

As for the micrometers, they are inherently more accurate, and I generally set my system up to ± 0.0005"
 

Cats Clause

Starting to get Involved
#4
Thank you Jim and Ron. Just to clarify:
I am aware of the difference between the digital and vernier calipers, they have both on site.
Ref the resolution of 0.000150", totally agree, hence the question.

This was picked up during an audit on measuring systems on the shop floor. During the audit I determined that VERNIER 0-6" calipers and MANUAL 0-1" micrometers, were both actually being checked to 0.015". I believe this is overly generous however and 0.0015" for verniers and 0.0005 for mic's more realistic?
 

Ron Rompen

Trusted Information Resource
#5
The resolution and calibration of your measuring instrument needs to be driven by the tolerance of the measurement. If you are measuring something with a tolerance of ±0.005" (total of 0.010") then your resolution needs to be better than .001", and your calibration also needs to be better than .001" (1:10 rule).
 

Mike S.

Happy to be Alive
Trusted Information Resource
#6
If you are measuring something with a tolerance of ±0.005" (total of 0.010") then your resolution needs to be better than .001", and your calibration also needs to be better than .001" (1:10 rule).
Ahhhh, the old "accuracy rules". They have caused a lot of problems and misunderstandings in their day and are rarely clearly defined as to exactly what they mean or intend to say, IMO.

And its not always a "10:1 rule" -- sometimes that is not even possible at the state of the art, and it is often not practical or necessary. Sometimes it is a 4:1 "rule" set by the customer.

ARP9013 states: "It is recommended that measurement capability meets or exceeds a 4:1 ratio between the product tolerance and the certified accuracy of the measurement device to ensure identification of nonconforming product consistent with the quality parameters."

But in any event +/- .015" for calipers or micrometers is way too loose, IMO. I always saw a maximum of +/- .0015" for calipers and +/- .00015" for micrometers.
 

Ron Rompen

Trusted Information Resource
#7
Yes Mike, you are correct; there are times when 1:10 is not feasible, or when the customer has mandated some other ratio.

calibration of a micrometer to ± .00015" is, in my experience, not realistic. Very few micrometers have a resolution to 5 decimal places, and the infintesimal difference in the half of a tenth of a thousandth of an inch is so reliant on operator bias and handling that, (again in my opinion) to even attempt it is futile. If I need to be measuring something THAT accurately, then I want something better than a micrometer :)
 

Mike S.

Happy to be Alive
Trusted Information Resource
#9
Yes Mike, you are correct; there are times when 1:10 is not feasible, or when the customer has mandated some other ratio.

calibration of a micrometer to ± .00015" is, in my experience, not realistic. Very few micrometers have a resolution to 5 decimal places, and the infintesimal difference in the half of a tenth of a thousandth of an inch is so reliant on operator bias and handling that, (again in my opinion) to even attempt it is futile. If I need to be measuring something THAT accurately, then I want something better than a micrometer :)
I'm not a metrologist. But our Metrologist at a former company lived and breathed metrology, it was his hobby as much as profession. He had lasers and all sorts of top notch standards in his lab. He was a metrology ambassador with some professional society, etc. He knew his stuff. He considered our Mitutoyo digital mics calibrated if they read within +/- .0001" or .00015" (I can't remember which) of the standard. I think .0001". We would use them for tolerances of +/- .0004 or higher.
 
Thread starter Similar threads Forum Replies Date
R Need of working standard for vernier and micrometer calipers General Measurement Device and Calibration Topics 2
C Work Instructions for Vernier & Micrometer General Measurement Device and Calibration Topics 9
A Micrometer anvil chipped General Measurement Device and Calibration Topics 19
G From an ISO 17025 auditor perspective must micrometer calibration check anvil flatness? General Measurement Device and Calibration Topics 4
G How to compute or estimate a micrometer or caliper flatness using optical flat General Measurement Device and Calibration Topics 2
G Procedure Creation specifically for dimensional (caliper, micrometer, dti) Document Control Systems, Procedures, Forms and Templates 8
W Standard for Micrometer Anvil Flatness Oil and Gas Industry Standards and Regulations 5
G Uncertainty Budget Examples for Caliper, Micrometer and Dial Gauge Measurement Uncertainty (MU) 3
G Caliper or Micrometer's Dimensional Flatness General Measurement Device and Calibration Topics 5
G Manual Procedure with Uncertainty Budgeting for either a Caliper or Micrometer General Measurement Device and Calibration Topics 6
M Uncertainty Budget for a Micrometer Measurement Uncertainty (MU) 5
M Laser Micrometer Suggestion (if any) for diameters that are +/-.0001 inch General Measurement Device and Calibration Topics 1
T A question on Calibration on In-line Laser Micrometer General Measurement Device and Calibration Topics 1
M Micrometer Anvil Placement to measure the diameter of Steel Wires Measurement Uncertainty (MU) 6
C One Inch Micrometer Calibration Method General Measurement Device and Calibration Topics 2
W Micrometer Storage while not in use General Measurement Device and Calibration Topics 4
D Can anyone share a completed Gage R & R on a Micrometer? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 10
W Thread Micrometer Standard Tolerances General Measurement Device and Calibration Topics 4
S Micrometer Calibration Using a CMM Calibration and Metrology Software and Hardware 12
5 Reasonable GRR result for a 0-1" micrometer with a total tolerance of .002" Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 16
M Calibration of a Micrometer used as a Standard General Measurement Device and Calibration Topics 5
S Laboratory to Calibrate Objective Micrometer needed General Measurement Device and Calibration Topics 4
W First Draft Micrometer Calibration Procedure ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 19
D Procedure on How to Calibrate a External Micrometer General Measurement Device and Calibration Topics 1
C Micrometer Parallelism and Flatness Calibration Requirements and Specs General Measurement Device and Calibration Topics 10
J Air Micrometer Basics - What are the internal parts and how do they work Manufacturing and Related Processes 7
M Trigonometric Calculation (V-Anvil Micrometer). I'm not getting it. General Measurement Device and Calibration Topics 6
J Calibration of Micrometer Reading up to Three Decimals General Measurement Device and Calibration Topics 3
K Calibration Procedure for ID Micrometer Calibration & Extension Rods General Measurement Device and Calibration Topics 5
4 Federal Specification GGG-C-105C - Caliper, Micrometer, Gage, Depth Micrometer General Measurement Device and Calibration Topics 7
D Determining Instrument Purchase based on Accuracy (Micrometer) General Measurement Device and Calibration Topics 3
A Generic or Specific Gauge R&R on Standard Equipment (ie.: Micrometer) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
P Micrometer Calibration Methods Calibration Frequency (Interval) 11
D What is the correct Working Standard for Digital Micrometer? General Measurement Device and Calibration Topics 21
D Laboratory where we can have parts checked for Thickness with a Laser Micrometer General Measurement Device and Calibration Topics 6
K Micrometer Calibration - Resolution, Accuracy and Range General Measurement Device and Calibration Topics 16
D Laser Micrometer for checking Thickness of Steel - Any Recommendations or Comments General Measurement Device and Calibration Topics 3
P How to Calibrate Laser Micrometer when no Calibration Company in the Country? General Measurement Device and Calibration Topics 3
M How to Fix the Standard Bar of a Screw Thread Micrometer General Measurement Device and Calibration Topics 9
D Results of a GR&R study done on a 0-1" Digital Micrometer Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
V Calibration Procedure for Thread Pitch Micrometer General Measurement Device and Calibration Topics 3
G Dispute - Checking a thin walled, round, hollow part with micrometer Inspection, Prints (Drawings), Testing, Sampling and Related Topics 25
C Seeking a holder/jig to calibrate large OD micrometer calipers (up to 23") General Measurement Device and Calibration Topics 8
T In-House Calibration - Digital Micrometer found Out of Calibration General Measurement Device and Calibration Topics 10
D GRR (Gage R&R) procedure for Mitutoyo Digital Micrometer wanted Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
P Micrometer Gage R&R study - Interpreting the data and suggestions Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
M Choosing a Laser Micrometer - Your recommendations? General Measurement Device and Calibration Topics 8
D Calibrating Lufkin ID Micrometer ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 6
B Using & Calibrating Ultrasonic Micrometer General Measurement Device and Calibration Topics 4
C Pin Gauge Calibration using a Micrometer - Accuracy & Calibration Level Question General Measurement Device and Calibration Topics 10

Similar threads

Top Bottom