What is air gaging?

Air gages were first developed in France before World War II by a carburetor company that was looking for a more reliable method of measuring its carburetor jets.

Air gaging is based on the law of physics regarding flow and pressure. They are directly proportionate to the clearance and will react opposite to each other. In other words, if there is more clearance there will be more flow but less pressure and with less clearance there will be more pressure and less flow.

In order to measure this, you must have regulated air pressure that flows through a restriction, and then through the nozzle in the air tool. As the clearance due to the workpiece is smaller, air flow is reduced, and the back pressure is increased.

In order to calibrate the gage for the task at hand, a known artifact (MEAN) or artifacts (MIN and MAX) are used to set the display on scale and report accurate and highly repeatable diameter sizes. These artifacts are certified master rings and/or plugs and are typically set at the Nominal or the MIN and MAX ranges of your tolerance. Different manufacturers use different methods of calibration.

Who uses air gaging?

Typically, air gaging is used at manufacturing companies that mass produce tight tolerance parts. It is also used to measure complex parts such as tapers even when not in a high production environment because of the ease and speed of which parts can be measured. This technology is used in automotive, aerospace, and medical applications.

Why use air gaging?

Air gaging is a very fast, efficient and reliable method of measuring. It is designed to be used on workpieces with tolerances of 0.005” or smaller. The resolution and repeatability of the measurement can be in the millionths of an inch. Because air gaging is a noncontact method, it is useful for measuring soft, highly polished, thin walled and other materials susceptible to marking. Air gaging is extremely easy to use and requires no special skills for the operator. Multiple operators will achieve the same or nearly the same measuring results when measuring the same part, thus taking operator technique out of the measurement results. This is a problem when you are using a contact gage such as a micrometer or dial bore gage.

Air gaging can be used to measure complex geometric tolerances such as diameter, taper, parallelism, squareness, flatness and matching of components in a very fast and efficient method.

Many of today’s columns and/or measuring computers can become an integral part of the manufacturing cell with communication to robotic loaders and the ability to send offset values to the machine, which allows for around the clock manufacturing with 100 percent inspection of workpieces.

Air gaging systems operate at air pressures that can remove contaminates such as abrasive particles and coolant, which will eliminate the need for a separate cleaning in most applications. The air tooling has no moving parts and therefore has a very long and dependable service life.

10 benefits of using air gaging:

1. Fast. The measurement is extremely fast. Great for 100 percent inspection of high-volume parts. Measurement takes only seconds and can be done inline, in many operations.
2. High precision measuring results. Air gaging can repeat measurements in the sub-micron range (millionths of an inch range) with a very high degree of accuracy.
3. No special training. Multiple operators will achieve similar results in measurements without special training. Ideal for the busy shop where everybody multi-tasks nowadays.
4. Easy to use. Goes hand in hand with no special training, as air gaging requires just a few quick steps.
5. Noncontact. Air gaging is noncontact and will not damage your parts. Sensitive components and delicate webbed structures can be measured without risk of damage.
6. Self-cleaning. Because the air is blowing across the surface being measured, any dust or coolant will be cleaned from the part. This saves considerable prep time and related costs for the shop.
7. No moving parts. This provides for longevity of the gaging system. If the air supply is consistent and clean, air gages can last for many years.
8. Small diameters. Air gaging can be used to measure extremely small diameters. Less than .6mm on an inside diameter is possible.
9. Taper measurements. Air is a quick and accurate way to measure tapers. Can display in degrees, minutes, seconds, taper per foot and many more.
10. Small lands or thin-walled parts. Will not distort the part on thin walls.

Where to use air gaging?

Air gages can be implemented on a work bench on the shop floor for quick first piece or 100% inspection depending on volume. It can also be incorporated into the measurement process with robotic loading for lights out production. They also are commonly used in the gaging lab for verification of parts from the shop floor.

This article is intended to give a basic understanding of when to use air gaging and how it might be of benefit in your shop. Even though it is an old technology, it is still one of the fastest and most accurate ways to measure. Air gaging technology is continually improving as computer technology continues to evolve. These systems can range from simple desktop readouts to full SPC computers with contour scanning capabilities. As manufacturing requirements continue to become more complex, air gaging technology evolves to meet the demand. For these reasons, air gaging will remain a viable measuring solution for generations to come.