Inspec Insights

  • Considering Recalibrating Your Calibration Cycle

    Jun 26, 2018

    How often should your shop calibrate a measurement device? That is an often-asked question, but one, like many, that has no one right answer. If money weren’t an issue, if time weren’t a consideration and backup gages were plentiful, then a decision might be simple; calibrate before and after every inspection.

    But, in the real world, many factors including cost, lost availability and calibration expertise come into play; and because gages will be dropped, fork lifts will bump CMMs, sensors and cameras will drop pixels, and every measurement device will eventually drift out of spec, calibration may need to occur when least expected.

    A simple internet search, “When should I calibrate my …,” will return a boatload of results.

    The National Institute of Standards and Technology (NIST), for instance, does not require or recommend any set recalibration intervals for measuring instruments, devices or standards. Specific recalibration intervals, NIST espouses, depends on factors such as the accuracy requirements of customers, requirements found in a job contract or regulation, the stability of an instrument or device, and environmental factors that may affect stability.

    Manufacturers provide mixed messages as well, some recommend calibration before and after a project while some propose calibration only when the measurement is critical.   

    Calibration vendors suggest a minimum of once per year but also caution that moves and other events could require additional calibrations.  To further confuse the matter, a common industry practice is to reduce the calibration interval by one half if a tool is out of tolerance. However, if it is within spec, the calibration cycle can be extended.

    Extending the time gap between calibration cycles is not necessarily wrong. Delaying calibrations is a tactic that can save money, at least in the short run, and can keep a measuring tool on the floor. Small shops trying to manage quality on a budget might find this plan appealing.   However, going this route requires that the person making the decision has all of the facts including calibration history, current tool usage and conditions and interim check results.  Data such as this will help determine the calibration schedule. Without it, parts might start to go out of tolerance even as production pumps out bad parts, blissfully unaware that they are making scrap. Calibration cycles can catch such conditions beforehand.

    Think of regular calibration as an insurance policy, it’s estimated that a $1,000 in calibration can save $1 million in rejected products.

    Calibration can do more than just help ensure against scrapped parts; it can also help track tool quality. Calibration can help determine when a measuring device needs repair or adjustment and just might extend a tool’s life. Or, it might reveal that the device needs replacing.

    Recording and analyzing calibration data can be a challenge. Developing control charts and spreadsheets can help determine if the device is precise and accurate. But, some shops calibrate thousands of gages each year, generating mountains of paperwork that cram filing cabinets and fill up hard drives.

    One option to tackle this mound of calibration evidence is to use a gage tracking program such as Inspec’s InspecGAGE Management software.  When comparing software you want to look for features such as monitoring of scheduled and unscheduled calibrations, reporting for management analysis and of course compare cost.

    To aid in the calibration decision, talking to a calibration house such as Inspec provides a good resource. Inspec calibrates a variety of equipment from master gage blocks to hand tools such as micrometers and calipers, measurement instruments such as force and pressure gages, electronic devices such as oscilloscopes, and even fragile or large equipment such as surface plates and coordinate measuring machines as well as many others.  Call us today to maximize your tool’s efficiency and minimize your calibration headaches.

    Leave a comment