In the production environment, where tight tolerances are a way of life, it’s critical to think about gaging requirements before putting instruments out there and possibly having them not meet expectations.
Mechanical bearings, including ball, roller, taper roller, needle, spherical and cylindrical, to mention a few, have been in use for hundreds of years, with countless designs, applications and sizes, and just as many measurement requirements that need to be defined and verified.
Measuring calipers have been around for nearly 150 years. In that time they have evolved into full-featured digital measuring systems. But it is a testament to the simplicity and versatility of the original design that the evolution has been so slow and that so few changes have been required to produce the instruments we are familiar with today.
Conceptually, the dimensional measurement process is quite simple. You get a drawing for a part-an electronic computer-aided design (CAD) file, blueprint, napkin doodle or whatever-which indicates certain critical part dimensions and tolerances: a particular diameter, for instance, must be 2.2370 inches ±0.0002 inch. All the manufacturer needs to do is to machine the parts to that dimension, then measure them to document that they are within the specified tolerance. What could be easier than that?
There are many ways to measure an outside diameter (OD), including scales, micrometers, calipers, coordinate measuring machines (CMMs), optical beams and vision systems. The choice depends on many factors including tolerance, run size, operator skill, part size and, of course, budget. An easy, fast, accurate and economical way of making such measurements is with an adjustable snap gage.