Calibration: Doing Your Own Thing
Before Doing Your Own Calibration, Consider these Costs.
From time to time we received requests to quote on the calibration of a large variety of items and then never heard from that potential customer again. Initially, we assumed our prices, delivery or both were not good enough and a competitor scooped the order out from under us. After looking into these situations, we found this was not always the case.
Often, the ‘competitor’ turned out to be the inspection department of the customer making the request. They wanted our prices to justify doing the work themselves. Using our prices they could go to management and say: “Look at what it’s going to cost if we send this work outside to what’s-his-face! We can do it cheaper in house.” And they had the numbers there to prove it—ours—discounted.
They may even quote some individual examples that show they can do a particular job in a hour, for instance, and their inspector would only cost $20 (plus benefits) compared to that outside lab’s price of $40. Of course, they usually forget to add the overhead cost per hour that could see their cost go to $50 or more.
I know the gentle souls who read this column would never stoop to such unfair comparisons, but if you’re thinking of doing your own calibration, there are some other costs to consider. They include:
Upgraded or new equipment to obtain the precision needed for the work
Calibration costs of your equipment whether you do it or have an outside facility do it
While your quality auditor may accept you calibrating your own tools, he or she may not be too excited about you doing your calibration equipment.
Better quality masters such as gage blocks, setting rods, plugs, etc., plus their calibration costs whether you are doing the work or using an outside laboratory
Upgrades to the work area if you don’t have a temperature controlled facility now
Staff training or upgrading
Quality systems. Many of your customers may be happy that you are registered to a ISO 9000 series standard but those who are serious about it will not be. Nuclear, aerospace, military and medical people may not be so enamored and expect accreditation to ISO 17025 as a minimum requirement since it refers specifically to calibration and/or testing laboratories and is a much tougher standard to meet.
There are other costs but crunching values for those listed will get you close to the actual cost of doing the work yourself. There are other considerations to take into account, the most important being the knowledge and skill of the people who will be doing the work.
If you don’t have someone on staff who has experience calibrating instruments and gages, you could find yourself in never-ending battles over measurements with suppliers or even other departments within your company.
Appearances aside, verifying the diameter of a plug gage requires more smarts and skill than doing the same thing on a machined part. Some inspectors seem to have a natural ability in this regard but most do not and will require a lot of practice to achieve it. Finding that high reading over a diameter when you’re dealing with millions of an inch or parts of a micron can be quite frustrating.
It would be advisable to test inspectors you expect to do your calibration to see just how suited they will be for the work—before you attempt to make a case to management for doing so. Such tests would include the quality and repeatability of gage block stacks they have wrung together. Get them to calibrate some instruments you would expect them to do in house. And get them to repeat it a couple of times over a period of time.
If you do functional tests such as these you’ll need some sort of objective score card to use for evaluating the results. And you’ll need to take measurement uncertainty into account when doing this.
If you’re not certain about that measurement uncertainty part of it all, you will have to get some training since it will become an element of your measurements that has to be dealt with.
If you’re thinking of doing your own calibration you have to know what you’ve got going into it all and what you’re likely to get at the end of it.