New to Calibration - Four Questions



Hello all, and thanks for having me in the forum.

As the thread title suggests I am very new to calibration. I work in the QA department an automotive engineering company in the UK and my management has decided they want to try and bring gauge calibration in house. Historically all calibration has been done by sending gauges to external companies. I have been tasked with researching the calibration processes in order to move this project forward. After trawling through endless information on the internet on various sites my head is starting to spin :confused:

Initially we want the in house calibration to cover thread gauges for machined tapped holes (M6x1.0, M8x1.25, M10x1.5 etc), go-no go plug gauges for un-tapped machined holes and digital vernier calipers. The plan is to have a set of externally calibrated master equipment which will then be used to calibrate all other gauges in house.

My question is can someone please give advise on:
  • what aspects of each of the mentioned gauges would need to be checked in order to meet correct calibration requirements? ie for a thread gauge checks should include major/ minor dia, pitch dia, depth step (where applicable) etc
  • what equipment would be required to calibrate the above mentioned gauges?
  • what documentation/ logs/ procedures would be required?
  • any other advise you can give someone starting out in calibration
Apologies for the length of the post. Basically I need to set up the calibration of these gauges from scratch and any/ all advise is much appreciated

Thanks in advance



Quite Involved in Discussions
In regards to the documentation - you will want a document explaining the calibration process of the items along with the allowable tolerance.

For the calibration report - you will want it to include:
* Calibration Date
* Next Calibration Due Day
* Name of person conducting the calibration
* How the unit was found - Was it intolerance of the previous calibration when you conducted the calibration?
* If any adjustments were needed - what were they?
* The calibration status of the equipment used to conduct the calibration.

Hope this helps.

Ron Rompen

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Just based on my own previous experience, plug gauges (GO-NOGO) are fairly simple as long as you are allowing yourself sufficient tolerance - you need something an order of magnitude 'better' than the tolerance you are using (example - if you are allowing a tolerance of ±0.0005" on a plug gauge, you need something with an ACCURACY of greater than 0.00005").
As for thread gauges, I would strongly recommend continuing to outsource them. Besides the obvious evaluations (pitch diameter, etc) there are other things that a good calibration lab can verify for you that you would be unable to do without investing in a lot of equipment and training.


The very basic start with calibration of threaded ring and plug gages would be to purchase the specifications to which they are made. Usually these specification will provide temperature requirements for inspection, tread forms and tolerance info etc.

Equipment wise you’re looking at a super bench micrometer, master set plugs for ring gages, and other calibration standards for plug gages. Work environment will need to be clean, temperature regulated and, typically for super mics, no air movement that is detectible.

Based on your customer requirements your calibration system may need to comply with ISO 17025 or be certified to 17025. Look at your national standards for calibration labs and UK’s very own National Physical Laboratory at Teddinton, Middlesex for guidance documentation. If I remember correctly NPL at one time had information of calipers, micrometers etc. free to the public via their website.


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Welcome to the wonderful world of calibration!
First, having been both in the third party and internal lab calibration environments I would alert you to the pitfalls of bringing the calibrations in house. You will not only need to obtain the calibration equipment and a properly controlled environment, you will also need to create an entire calibration program. This will include setting up a calibration recall program, establishing a calibration history database, maintaining the calibration - and traceability - of your lab standards, producing and storing calibration records, training programs, a recall system for out of tolerance standards, etc. All the things that your current calibration providers are doing in the background. And you need to do this well enough to achieve whatever quality and program requirements that your products are committed to meet, especially to the point of being "audit proof". A good amount of time, effort and money will need to be dedicated not only to establish such a program, but also to maintain it.

A lot of this will depend on the volume of work involved, and available equipment. To calibrate the thread plugs and plug gauges you will need, at a minimum, a supermicrometer / horizontal measuring machine, a set of thread wires, and the accessories needed to make these measurements. If you need to purchase these you will require a large work volume to justify the high costs involved. These are also time consuming calibrations, the thread plugs requiring an advanced skill level. Plan on the labor costs involved as well. For the calipers you will need, at a minimum, a set of gage blocks that cover the length range of your calipers, a surface plate, ring(s) for the inside jaws, etc. All of this needs to be done in an adequately controlled environment.

In the end, the practicality of taking on the calibrations yourself will boil down to the work volume, equipment required, labor costs, and setting up a calibration program. I know that here in the States that mechanical calibrations tend to be inexpensive, so in most cases it is not economically feasible to do them yourself. But if it makes financial sense in your situation then got for it!


Hello all, and thank you for the replies. All good information to take on board. As mentioned I have no experience in calibration and am starting off from scratch so all information is welcome.

At the moment Im trying to put together the information to show the feasibility of launching such a project in house and my head is spinning with information regarding 10:1 rules, 3 wire methods, uncertainty etc

With regards to an environment, we have a large QA lab which houses our CMMs along with other equipment such as tensile/ hardness testers, profile projector, metal spectrometer, and is clean, temperature controlled etc. It needs to be to carry out the appropriate dimensional checks on our products. The plan is to dedicate an area within this lab to calibration equipment and carry out all calibration measurements there.

The big thing will obviously be the cost associated with getting the right equipment. As a large engineering company we have any amount of micrometers, but whether any of them are accurate enough to preform calibration is another thing :confused:
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