Whether you’re a small machine shop or a large multimillion-dollar manufacturing giant, there’s no doubt you use dimensional gauges to maintain the standards for quality in your production.

The accuracy of these dimensional measuring instruments must be periodically checked to ensure that they’re correctly performing the job for which they’re intended. And whether you’re a small shop or a large one, more requirements are being set to document this performance and ensure that all gauging is under control.

In fact, accepted standards call for all manufacturing operations to calibrate regularly or prior to use all inspection, measuring, and test equipment and devices that can affect product quality. They must calibrate their equipment against certified equipment that has a known valid relationship to nationally recognized standards. If there are no predetermined standards, then the basis used for calibration must be documented.

Maintaining and checking the performance of hundreds or thousands of gauges can be a costly proposition, whether you buy the calibration equipment and hire people to do the verifying in-house or send the gauges to an outside calibration service to perform the checking for you. For smaller machine shops, the most economical approach is usually to hire a calibration service to do this verification.

But where’s the break point that determines when to document gauging performance internally or have it sent out to a calibration service? Is there a hybrid option? Can you use internal resources for some of the more basic instruments while using an external service for other, perhaps high-performance items?

What do you have on hand now?

If you already have a quality control department that’s responsible for checking parts, there’s the potential for doing the internal checking and calibration of some of your own basic measuring tools—such as calipers, micrometers, and dial and test indicators. You may already have the standards and equipment, such as a set of gauge blocks, to do much of this calibration work.

Being universal, gauge blocks could be used for all of these items, though they would be a bit cumbersome for checking the dial, test, and digital indicators. This is because of the number of data points needed and the handling of all the gauge blocks.

However, for about the same price as a good set of gauge blocks, the investment in a dial indicator calibrator would cover the calibration of all the basic hand tools in your operation. With your set of blocks and the calibrator, you’d have all the tools needed to consider doing the work in-house. It’s a decision to think about with all the time and handling associated with sending your tools out.

But as the standards point out, the items under test must be verified using certified equipment that has a traceable relationship to a nationally recognized standard. So in this case, the gauge block set might be the only item that would need to be sent out for periodic calibration to ensure the blocks are at their prescribed accuracy. Thus, your gauge block sets become the traceable standards needed to meet the requirements for documenting the performance of all your gauging instruments.

Besides having the traceable standard to do the work internally, you must have, and show that you have, procedures in place that are followed when calibrating the instruments. This is where the real work comes in, at least initially. You must be able to document that you have the traceable tools, trained operators, and procedures to do your own instrument verification.

There’s also work in establishing your sources of error in the measurement process. No small task for sure, but you probably have procedures in place now for part inspections and other processes. So you already know how to comply with these types of requirements.

With the proper standards, instruments, people, environment, and documentation, you have all the tools necessary to get your dimensional measuring instruments periodically checked for their performance and ensure they’re accurately performing the job. That helps you fulfill the goal of meeting production requirements in the most cost-effective way.

Published on the Mahr website.