Frequently Asked Questions (FAQ)

Air gaging relies on the relationship between air flow, pressure and clearance.  As the clearance between the measuring nozzle and the part changes, the air flow and pressure change proportionally.  The readout measures the back pressure created when the nozzle is brought in close proximity to the workpiece.  The actual reading is “comparative measurement” to a precise master that is calibrated and used in conjunction with the air gage tooling for the application.

The alternatives to air gaging are micrometers, CMMs, bore gages and other manual gages.  These methods require experience, skill, technique and consistent training and may produce variable results depending on the equipment and the operator.  With air gaging and its masters, results are not only consistent, but also accurate and repeatable. 

Some benefits to using air gaging are:

• Non-contact = less wear and tears on the part and the tool
• Air pressure = helps clean debris, dirt or contamination that can influence results
• User-friendly = easy to teach, easy to use, easy to set
• Accurate and precise = limited use due to tight tolerances using setting masters
• Fast and repeatable = virtually no variation in readings and results
• Allows you to measure deep bores where other gaging would be limited. Tooling is specifically designed and built for your application

A master is a calibrated reference standard used to zero or calibrate the gaging system.  It is a physical object, like a plug, ring, or disc, with a precisely known size that acts as a reference point for measuring the dimensions of workpieces.

• Master Rings are used to set air probes and other types of bore gages to a known size.
• Master Plugs are used with air rings and other external diameter measuring instruments as setting standards. Depending on whether single or dual masters are required, single or double-ended aluminum handles are utilized.
• Master Discs are used for the same purpose as master plugs, except that these members incorporate plastic grips on each end, rather than aluminum handles

The dual master system user calibrates the readout by observing that the span displayed by the readout corresponds to the span between the minimum and maximum setting masters.  This method set the combined sensitivity of all the components of the gaging system at one time.  The sensitivities of components such as flow restrictors, amplifiers, pressure indicators and gaging nozzles, as well as pressure drops in air lines, are included in one overall calibration; thus stringent control of individual components is not necessary to obtain accurate overall results using a dual master system.

The single master system requires controlling the sensitivities of both the gage readout and the air gage member at the factory prior to shipment.  The sensitivity of the air gage readout is verified using master orifices that simulate air flow to the gage nozzles and the gaging member sensitivity if controlled by precise finishing of the gaging nozzles with verification using factory setting masters. Ease of set up is the principal advantage of readouts configured for single master operation, though significant cost savings may also be obtained in large gage sizes by eliminating the cost of a second master.

Single master system accuracy – An allowance must be made for possible scaling errors in both the comparator and the gaging member of the single master system.  The effect of scaling error increases in direct proportion to the span between the master and the point of measurement.  For instance, if a measurement is made .0002” from the mastered dimension, a scale factor error of 5% would cause an error of 5% of the .0002” span or .000010”; if the span were extended to .001”, this error would become .000050”.  An error allowance of 5% is a reasonable assumption considering that inaccuracies of manufacture and stability with age must be allowed for in both the gaging member and the comparator.  For most applications, this is an acceptable level of accuracy.  Users should be aware, however, that the use of a master that is well outside of the tolerance zone may lead to unacceptable errors in some applications.

All gages are custom-manufactured per the customers’ specifications.  We do not stock finished gages. Please feel free to complete the “Request A Quote” form.

To obtain a quote, it is helpful to provide the following:

• A drawing or a sketch that highlights what you want to measure
• Diameter (in or mm), tolerance (min/max) and datum points
• Bore Depth and Length of the area to be measured
• Size of “Land” or area of part to be measured
• Is the bore a thru-hole or a blind?
• Are the sides smooth, rough and are there obstructions along the walls of the diameter?
• Which readout or comparator are you using, if any? Which make and model?
• Are you measuring an ID (probe) or OD (ring)?

• Precision parts where inside or outside diameters must be precise like linear bearings and their cages.
• Match-fitting parts like pistons and sleeves for hydraulic applications used in aircrafts, military and transportation applications.
• C-Snap Gages provides open access making for a convenient means to measure shaft OD while still mounted on a grinder.
• Automotive applications where precision bores and pistons must have precise clearance.
• Medical applications like femoral stems and ball sockets require self-holding precision fit where tapered gages can measure angles.
• Rifling application with precise measurements of groove and bores diameters. Rifling gages are a good application to be able to gage deep into the bores

Depending on the application and air gage type, in some cases as narrow as .050”. In some instances we can use a Leaf Style gage (contact point) to check lands down to .010”

Accurate dimensional measurement requires readouts and gaging members that are calibrated with known standards.  Both single and dual master methods of calibration are widely used for air gage systems.  The selection of one over the other involves trading off the flexibility and accuracy of the dual master system versus the ease of set up and economy of using the single master system.  Properly applied, both systems provide acceptable levels of accuracy.

The dual master system user calibrates the readout by observing that the span displayed by the readout corresponds to the span between the minimum and maximum setting masters.  This method sets the combined sensitivity of all the components of the gaging system at one time.  The sensitivities of components such as flow restrictors, amplifiers, pressure indicators and gaging nozzles, as well as pressure drops in air lines, are included in one overall calibration; thus stringent control of individual components is not necessary to obtain accurate overall results using a dual master system.

The single master system requires controlling the sensitivities of both the gage readout and the air gage member at the factory prior to shipment.  The sensitivity of the air gage readout is verified using master orifices that simulate air flow to the gage nozzles and the gaging member sensitivity is controlled by precise finishing of the gaging nozzles with verification using factory setting masters.  Ease of set up is the principal advantage of readouts configured for single master operation, though significant cost savings may also be obtained in large gage sizes by eliminating the cost of a second master.

Single master system accuracy. An allowance must be made for possible scaling errors in both the comparator and the gaging member of the single master system.  The effect of scaling error increases in direct proportion to the span between the master and the point of measurement.  For instance, if a measurement is made .0002″ from the mastered dimension, a scale factor error of 5% would cause an error of 5% of the .0002″ span or .000010″;  if the span were extended to .001″, this error would become .000050″.  An error allowance of 5% is a reasonable assumption considering that inaccuracies of manufacture and stability with age must be allowed for in both the gaging member and the comparator.  For most applications, this is an acceptable level of accuracy.  Users should be aware, however, that the use of a master that is well outside of the tolerance zone may lead to unacceptable errors in some applications.

Yes, Western Gage’s state of the art calibration lab is ISO/IEC 17025:2017 Accredited.

See this page for cert and scope of accreditation.

The two videos below have more information: