In the ‘40s, air gaging might have been considered the greatest thing since sliced bread. While sliced bread was busy becoming mainstream, air gaging brought just as exciting a breakthrough to the shop floor. You see, at this time—long before electronic probes and amplifiers—it was very difficult to achieve a 50u”/1um resolution on the shop floor. The most common readout used at the time was dial indicators or dial comparators. However, being mechanical, they had issues when used at the point of manufacture, including wear, repeatability, contamination, lack of robustness, etc.
When air gaging was introduced, it provided the first high-performance 50u”/1um or better gaging on the shop floor. In fact, air gaging provided two breakthroughs for dimensional measurement. The one most of us are familiar with today is the use of small orifices or jets built into tooling and used for dimensional comparison. The other and often forgotten technology was the air probe—a contact probe very similar to the LVDT probes common today—but functioned by the contact tip of the probe opening and closing a tapered valve in its body. About 30 years ago, this technology began to be replaced by LVDTs/digital probes/digital indicators that were becoming more robust and economical.