"Stylin" With Your Caliper


 George Schuetz, Mahr Federal Inc.


Convenience is one of the reasons the caliper is often the tool of choice for length/diameter measurements. The basic caliper provides direct size information quickly, has relatively high resolution, and is easily adaptable to many different measurement applications. Beyond the basics, there are all sorts of caliper styles, which extend these advantages to many special measurement applications.


A caliper consists of two opposing surfaces, a stationary anvil/jaw and a moveable slide. On most calipers, these are hardened steel, but they can be purchased with optional carbide-tipped or ceramic contact surfaces. However, calipers can also be equipped with built-in contact tips with unique forms for measuring special part characteristics, or even jaws with replaceable and configurable contact points.




If walls could talk. When measuring or exploring the wall thickness on cylindrical parts, the two flat surfaces of a standard caliper will cause measurement errors since one jaw will measure a chord rather than a line contact. To do this measurement properly, one of the jaws needs to be cylindrical in shape. This allows for a line measurement on both the ID and OD of the part for true wall thickness.



In the groove. Measuring the outside or inside diameter, or the width of a machined groove calls for still another type of caliper contact blade. Often these grooves can be so narrow that neither a standard nor reduced face caliper will fit completely into the groove. Pointed blade contacts, as the name implies, are very slender and flat. They nest readily into narrow-bottomed grooves. Other versions have a configuration that funnels down into a very narrow point for getting into deep groves. These very narrow tipped jaws fit into very small grooves and tracks, making many previously difficult ID and OD measurements far easier. Excessive pressure on these narrow blades—e.g., while the tool is being rocked to find the true diameter—can result in premature wear.



Even more grooves. But wait—not all grooves are created the same. There are grooves or recessed IDs and ODs that a typical caliper cannot get onto. For these applications two other special jaw configurations are available, one series for IDs and the other for ODs. The point jaw is ideal for measuring wall thickness, grooves and recesses, while the flat jaw type is designed for measuring grooves and recesses primarily on ODs.



Getting to the center of things. Calipers with tapered jaw tips are especially designed to measure center-to-center distances on holes. Often one of the jaws is adjustable in height to allow for measuring holes on offset planes.



Speaking of offset planes. Often, parts are not nice and square but have obstructions that need to be measured around. Usually the standard reference jaw on a caliper can also be adjustable on its height. This allows the main scale jaw to slide up and down to facilitate measurements of stepped sections on the part. Now these hard-to-get dimensions become a piece of cake.



Reaching for it. Knife edge jaws with extra-long reach are designed for those parts that are deeper than the reach of a typical caliper. By being over 50% longer than a standard caliper they allow for those deep hole applications.


Even the best and most basic hand measuring tool can be made better by adapting it to special application requirements. By choosing the most appropriate style for the application, you will achieve a faster and more accurate measurement. Each style, however, has its own unique requirements for care and use. If you are going to measure with style, make sure you know how to do it properly.