Other Dimensions: Single Source Calibration
“Reduce the supplier base” thinking is one variation on the theme that is finding its way into the quality department and the purchasing of calibration services in particular. A reduced vendor list may lower costs in the accounting department but can create problems in the quality department that cost many times more than the anticipated savings.
Applying this sort of process means one has to assume all laboratories are equal, something that experience shows is not the case.
Most laboratories have one area of metrology they are best known for, where their greatest expertise lies. When they begin expanding into other areas they may have staff that are generally knowledgeable-or not-but they may not have all the hardware or the environment that different branches of metrology require.
To make up for such deficiencies, work gets subcontracted to facilities that specialize in that area, which means higher costs to the end user of the service. Sometimes laboratories that specialize in a single branch of metrology are not that well equipped either, and they have to subcontract significant portions of the work received.
The calibration of thread gages is an example. There are many labs out there calibrating them, but when it comes to thread ring gages, many do not have, nor will they buy, the full suite of setting plugs to calibrate them. And, of course, when special thread rings are involved, few labs beyond those who make such gages will have the setting plugs.
We frequently run into situations where the labs involved have problems calibrating thread plug gages. Many accept the markings on the gage handle as the base criteria and are not able to confirm what the pitch diameters should be. Others use software that is technically correct-but doesn’t agree with published standards that take precedence over computer-generated numbers at this time.
Some folks calibrating thread gages don’t have any means of measuring the thread form, and despite this lack of basic hardware, can be accredited to measure pitch diameter while ignoring the thread form. If thread gage calibration is a sideline compared to the other items a lab calibrates, they cannot justify buying the right equipment to correctly do the job. So the customer ends up getting gages that are only partially calibrated.
Very few independent laboratories of any stripe have equipment to measure linear pitch on a thread gage with any reasonable level of uncertainty.
Some folks think calibration is a simple matter of reading some instruments and that no other knowledge is needed beyond what is in the instrument’s user manual. They don’t realize there’s something called expertise involved-until they need someone to explain why a gage is rejecting their parts when direct measurement indicates they are within limits, and the gage has been calibrated and also found to be within limits. If you are facing the possibility of thousands of parts being rejected or legal action because of part failure causing injury, you can’t afford to deal with a laboratory that lacks expertise.
Expertise includes experience that can provide answers quickly because your problem may not be the first time it has been encountered. In addition, expertise requires technical knowledge of the way gages and instruments are made and what situations arise as a result of those processes. In addition, the core principles of metrology must be understood by the technician to ensure adequate calibration is provided.
Of course, none of this means anything to the folks in accounting because they don’t have to deal with any fallout that results from their edicts on cost reduction. They understand dollars, not metrology, so when they ask you to single-source your calibration, ask if their department will cover the costs when things go wrong. They won’t gamble with their money but will have no problem risking your budget.