Today, we are going to talk about how air gaging has played an important role in precision metrology for decades and how Mahr air gaging provides top of the line air gaging equipment. Since the 1940s, air gaging has been one of the most reliable high performance measurement systems available. Back in the mid-20th century, there simply were fewer electronic capabilities and optic tools available for precision measurement purposes. Air gaging served as the first way to complete measurements during manufacturing down to 50 millionths or one micron. From there, air gaging has remained one of the most valuable ways to complete tough measurements due to the specialized features that come with working with air.
Air gaging basics
Okay, let’s talk about what sets air gaging apart. As a fixed-variable gaging system, air gaging uses comparative measurement that provides variable data, making it a highly accurate method for taking dimensional measurements. During data collection, you can get actual deviations or learn about the process trends in order to diagnose any manufacturing issues and make necessary process improvements. The build of an air gage is specific to the dimension being measured. While this makes the tool more limited in terms of it measurement range, it also makes it incredibly good for measuring the specific size being assessed and therefore helps in decreasing operator influence. In fact, air gaging is one of the fastest and easiest measurement methods due to the operator applying the air tool only to the specific part that is being measured. Additionally, accuracy is built into each air gage through a single master system, which requires a single setting master to establish the initial zeroing. Up front, the cost of a Mahr air gage can be high, however, these tools will last for decades with regular system maintenance which evens out the cost and leads to improved measurement overall.
How air gaging works
The fundamentals of air gaging are very similar to the functioning of the average garden hose, with the replacement of air for water. If you were to hold a garden hose up against the side of a building, as the distance between the nozzle and the surface becomes smaller, the water flow restriction increases resulting in an increase of pressure. As you move the hose closer to and further away from the building, you can alter the pressure of the water. This same principle can be applied to air gaging when considering the intensity of the back pressure of air flow. This is known as the pressure distance curve and is central to understanding the air gage.
The pressure distance curve
The pressure distance curve is found when you put a restrictive force or surface in front of the air stream coming out of the air gage. Then, when you plot the points of distance versus the pressure of the air against the surface, you create a pressure distance curve. Within the resulting curve, there will be a linear portion that is used to measure the dimensions of interest. Air gaging is an easily repeatable process when you control for the different factors that may influence this curve. When using the Mahr air gage, you will want to control the air pressure being used, the position of the air jet or the hole the air is flowing through, and the manufacture of the air plug, and then calibrate them into a known pneumatic zero. In this way, you can easily repeat the pressure distance curve within multiple applications. The precision is manufactured right into the air tooling, the readout system, and the reference standard, making them all interchangeable allowing you to have a known performance within the air gaging system.
Application of air gaging
Air gaging is just like any other type of gaging that you may be utilizing for precise measurements. A snap gage, a bore gage, a plug gage, and an air gage all require the same information and similar application. You want to know the size you are trying to measure, the size tolerance at the location of the measurement, and the specific surface finish involved. One piece to emphasize with the application of an air gage is to know the specifications of the size and tolerance of the part being measured. Due to its specific design, an air gage is very well matched to the measurement being completed, which requires complete accuracy and understanding of the application it will be used in.
Surface finish in air gaging
Air tooling works because air flow is restricted through the hole it flows through, thus creating a back pressure. The orifice where the air flows has a diameter of about fifty thousandths that measures over a particular surface. Surfaces naturally come with specifications about their finish regarding degree of roughness. Due to the roughness, the air gage must accommodate for navigating the peaks and valleys as it creates back pressure. Whereas a contact measuring system would ride the peaks of a rough surface, an air gaging system fills in and averages the location of the peaks and valleys on the surface as it builds back pressure. Due to the influence of roughness on the finish on the part being measured, knowing the surface finish is important to the application of an air gage, particularly as the tolerance gets tighter.
Why to consider using air gaging
Air gaging is a specified comparative measurement system designed for a particular dimension of interest. The Mahr air gage is self-aligning, fast, and simple to use. Due to the specificity of the design of an air gage to the dimension being measured, there is practically no operator influence on the output, increasing the precision capabilities of this measurement method. Since the sensing mechanism of the air gage never touches the dimension, this tool is considered no contact. Additionally, the air used to sense in combination with the back pressure air flow helps to clear away any liquid contamination on the surface of the part. All of these qualities help to minimize potential accuracy confounders and increase precision at the point of manufacture.
When to consider using an air gage
Air gaging is particularly useful when working with tight tolerances. Over the past number of decades, tolerances have become tighter and tighter. Air gaging allows for taking an accurate look at tolerances despite this continued increase in tightness. Specifically, if the tolerance is tighter than a thousandth and a half (or 40 microns), the air gage is the perfect tool. Plus, when you are using the Mahr air gage, you can get a high resolution up to 5 micro inches or 0.1 microns. The Mahr air gage can be used to measure sizes ranging as low as 3 millimeters, up to more than 1000 millimeters. The variable data produced by air gaging allows for you to know by how much a particular part is aligned with where it should be or off the mark. These tools can be particularly helpful when you have a high volume of parts due to the minimal need for operator involvement and speed of measurement. When taking geometric measurements, such as when working with tapers, straightness, or diameter variation, the Mahr air gage is a great tool. Finally, when working in an environment that has a risk of liquid contamination, the air gage automatically eliminates any concern, because of how the air flow is applied.
What an air gage can measure
The concept of back pressure as the mechanism of measurement allows you to complete a number of measurement goals using an air gage. You are able to measure length or thickness of a part. You might also collect geometric data such as taper, squareness, straightness, or center distance of a part. You can also measure outer diameter either through an air ring by turning the air plug inside out, or by an air snap that can measure outer diameter when the part remains in the machine. You can also combine an air ring and an air snap in order to determine the distance of clearance between two mating parts. While the air plug is the best common way to find diameter, a number of additional form conditions can be determined using the air plug. By moving the air tool up and down, you can determine diameter size, by rotating the air plug you can assess orbitality, by exploring a bore you are able to find barrel taper and hourglass shaping, and you can even look at two-point or even loading conditions.
Parts of an air gaging system
The readout, the master, and the air tool are the three central parts of an air gaging system. The air tool may be the most critical part of an air gage because it is the air tool that sets the reference that the dimension is compared to during the measurement process. The air tool consists of a hardened steel cylinder within an air plug, through which air passes and exits through a pair of opposing air jets. The pressure builds when the jets are closed off and the airflow is throttled. Then the back pressure is created, which is used in order to create the pressure distance curve. The air gaging system then measures the back pressure in order to provide data on the size of the part.
Air plugs
The highest number of variations found within an air gaging system are found with air plugs. Depending on the body style, you can have thru holes for thru hole bores, blind or super blind holes for measuring the bottom of the bore, relieved or non-relieved longer body lengths for continuous diameter or a measuring diameter that is brought down to a clearance diameter, and stop collars in order to set the air jet at a particular depth or match it up with a small land on the bore. Air plugs are also customizable based on the number of jets you require. The two jet air plug is the most common choice for inner diameter and outer diameter measurements. The three jet air plug is best when the part has an odd number lobe form error. Having four jets allows you to average the diameter reading across two diameters that are 90 degrees from each other. Having six jets allows for an average of the two and three lobe roundness. Depending on your measurements needs, customizing the air plug in an air gaging system can be very helpful.
Air rings and air snaps
When finding the measurement of outer diameters, specifying the air ring and air snaps may become useful. Air rings can be configured for two or three jets and the jets may be located at various spots from the face if you are looking to target a specific part or a specific land on the part. Air rings can either be a bench or they can be in a portable device. Air snaps are used at the point of manufacture and can be made with single or multiple circuit configurations. Finally, a piece very similar to a stop collar can help to align an air snap to a particular location on the outside diameter or multiple circuits can be used to get a taper or taper checks on the outside diameter.
Display options on the Mahr air gaging system
Mahr air gages may be mounted on a bench, computerized, or portable. Each version comes with a range of display options to help you get the most functionality out of your tool. The Dimensionair display is an analog display system that provides a fast and rough output. Dimensionair can be built with smaller or larger dials, and is easy to adjust with a single zero setting. This popular product works well for bench mounted work stations. Alternatively, the micro Dimensionair unit, or µDimensionair, is a portable, handheld version of the display system that provides actual values and tolerances. As our lowest cost display option, the µDimensionair is perfect for machine inspection and can be configured in a number of different ways to maximize comfort. Mahr also sells bench mounted digital display options like the digital Dimensionair, which comes with a single or dual input. The digital Dimensionair is a full feature bench amplifier with actual values, tolerances, normal reverse polarity, data output, and more. You can also complete multiple dimension measurements with use of its side-by-side readout and large three color display. Finally, Mahr supplies computer-based system readouts, with the C 1700 PC with cockpit and N 1700 modules. The Mahr cockpit software is easy to use and comes with a variety of hardware modules including USB interface, LVDT’s, air tooling, and I/O’s. The Mahr cockpit software has user definable programming to customize the gage solution for taper applications, multiple diameter checks, and multiple stations.
What sets the Mahr air gaging system apart
At Mahr, they have the equipment to not only manufacture air gaging systems, but also to measure all results as compared to high level standards. All Mahr measurements are traceable to the United States standard, Mahr grand master primary standards, and NIST certification standards. The Mahr manufacturing set up includes a metrology lab that is ranked one of the highest in the world due to the ideal environmental control in place. The regulated temperature control, complex air filtration system, and independently supported 375 ton concrete slab all reduce vibration, temperature fluctuation, and air contamination from the environment. The entire Mahr precision measurement center is fully certified by NAV lab, ISO 9000, and NQA.
Conclusion
Mahr has been working in the field of air gaging since the 1940s. In this specialized form of metrology, Mahr excels at providing high quality standards and reliability, along with ongoing improvement and progress. Air gaging was one of the first reliable ways to engage in precision measurement. Using a fixed-variable system, air gaging provides variable data on dimensional measurements. In a process that is highly specific to the particular measurement needed, air gaging decreases operator influence, is simple to use, and provides fast data output. Through customization of the display, air plug, air snaps, and more, you can find the perfect Mahr air gaging system tool for your metrology needs. Mahr labs knows metrology, and they apply air gaging manufacturing under the highest quality commercial certifications available. Contact Mahr today to hear more about the particular air gaging features and options for your measurement workshop.
FREQUENTLY ASKED QUESTIONS
- Can you tell me more about the Millimar D-series Mahr air gages?
The Mahr Millimar D-series air gages include the Millimar D-4000, Millimar D-8000, Millimar D-32000, Millimar D-16000, Millimar D-5000, Millimar D-2500, Millimar D-10000, and Millimar D-1250. These air gage tooling systems are operated with regular workshop compressed air. With an internal regulator, the Millimar D air gages keep the air pressure within the tool within the calibrated range. You can easily zero offset the tool with only one setting standard and the zero adjuster. The display is clearer than ever with fine scale graduation and a needle-thin pointer, allowing for an accurate read out every time. No recalibration is required after you change out any of the measuring equipment, allowing you to continue on with your task after setting the tool to zero. Each air gage includes an air filter integrated into the machine to help clarify the air as it is pressurized. There is an equipment connection on the front of the air gage for easy access, and all you need is hand tightening for any tight connections. These air gages use Dimensionair and are compatible at the federal level. The analog display ranges between plus and minus .0015 inches, and the graduation value is .000025 inches. This tool has a magnification of 4000 to 1 and comes with an input for pneumatic measuring equipment. The scale reader dial has a diameter of 152.4 mm or 6 inches. The Mahr Millimar D-series air gage package includes an air filter, a supply hose AHO-2, and an adapter for pneumatic gages. Finally, you can get your Millimar D-series air gage tooling system with any of the following accessories: a magnification kit, a particle filter, an oil and water separator trap, and a replacement filter.
- How has the manufacturing process of Mahr air gaging tools advanced?
Mahr is constantly working to improve the process of manufacturing their air gaging systems in order to better serve the metrology community. At this time, the process for creating the air plug requires the operator to enter four parameters into the machine at which point the machine simulates the part to be manufactured. The operator adds some finishing touches to the air plug and within 24 minutes of processing time, the part is produced. Using this technique, Mahr has successfully fine-tuned manufacturing to a very efficient process. This efficiency has resulted in a major reduction of time required for processing, which leaves the machinery open for more specialized air tooling requirements. Additionally, because Mahr needs less time to build the parts, the delivery time for customers has also been dramatically reduced. Following a customer order, the air plugs with uncertified masters are scheduled for two-week deliveries, with a certified master having a three-week delivery. As Mahr continues to improve these processing procedures, you can expect to see further production enhancements and faster service.
- What types are materials are used for the manufacturing of Mahr air gages?
At the heart of Mahr’s air gage tooling focus is how to make a better tool. One important factor in the metrology field is material. Different tools and different settings require different materials to be used. Currently, Mahr is beginning to reduce the amount of chroming that is required in the processing of air gages, with the ultimate goal of eliminating chroming from the process entirely. Chrome is an expensive material and it is hazardous to both the environment and people. Unfortunately, chrome is susceptible to flaking or chipping when mistreated or accidentally damaged. Now, Mahr is using an aluminum chromium nitrate based vapor deposit system for the processing of special air plugs instead of using chroming. Aluminum chromium nitrate has a very high resistance and is extremely hard, allowing it to have high shock resistance. Additionally, this material is resistant to rust, which eliminates the need for chroming to prevent rusting of the tool. In fact, air plugs made with aluminum chromium nitrate will be longer lasting than their predecessors. Stay tuned for more information on further air gage processing improvements at Mahr.
GLOSSARY TERMS
- Air gaging
Air gaging is a precision measurement method that applies the laws of fluid dynamics to determine dimensional variation. Using an air gage tooling system, air flow pressure is increased or decreased to create the pressure distance curve. Air gaging is the only metrological technology that is able to get so many high precision points so close in a variety of configurations. Whether you need to measure taper, straightness, squareness, or complete part qualification, air gaging can be applied with a high level of accuracy.
- Air plug
An air plug is a part within an air gaging tooling system. The air plug is built from a hardened steel body that has two or more air gage nozzles. Air passes through the air plug to the nozzles where the back pressure is produced by resistance from the surface of the work piece being measured. The body style of the air plug can be adjusted to accommodate different measurements. For example, when measuring the bottom of a bore, you may want a blind or super blind air plug. Air plugs can also be customized by the number of air jets or nozzles they have. For example, a two jet air plug is ideal for inner and outer diameter measurements, whereas a three jet air plug can be used when the part you are measuring has an odd number lobe form error.
- Air ring
An air ring is a part within an air gaging tooling system. The air ring is make of a thermally stable material, usually steel, and can be used to measure air pressure and to determine the external diameter of a part. Air rings can be customized to have two or three jets, with jets located at different areas of the tool depending on the intended measurement. Air rings are set up to be bench mounted or portable.