Mastering sets the air gage against known sizes so every reading after it is accurate. Done routinely and correctly, it prevents most measurement problems; when readings do go wrong, the symptom usually points to the cause.
When to master
- At the start of every shift
- After changing tooling or the readout program
- After a change in temperature or air supply
- Whenever a check on the master shows drift
- At any other interval your quality plan requires
How to master
Dual Master
- Clean the gage and both masters.
- Insert the MIN master and set the low point.
- Insert the MAX master and set the high point. The readout adjusts its span to match the difference between the masters.
- Recheck the MIN master to confirm.
Single Master
- Clean the gage and the master.
- Insert the master and set zero at its certified size.
- The span comes from the factory-matched sensitivity of the tooling and readout, so they must be the same amplification.
For the difference between the two systems, see single vs. dual master air gaging.
Reading the results
- Check the master size. Enter the certified size from the master's certificate, not just its nominal.
- Use a master near mid-tolerance for Single Master gages. Scale error grows with distance from the master.
- Surface finish matters. An air gage reads the average surface under the jet, so on rough parts it can differ from a contact gage or CMM. Correlate the methods before comparing numbers.
- Prove the gage. A gage R&R study shows how much of your tolerance the measurement system uses.
Troubleshooting by symptom
| Symptom | Likely causes |
|---|---|
| Readings drift during the shift | Temperature change in parts or masters; supply pressure dropping below the regulator setting |
| Readings jump or won't settle | Water or dirt in the air; loose fitting; part not fully seated |
| Won't master, or the span won't set | Leak in the hose, fitting or O-ring; blocked restrictor or jet; wrong tooling for the readout |
| Master check is off after mastering | Dirty or damaged master; masters swapped; wrong master size entered |
| Different operators get different results | Plug not fully inserted or ring tilted; parts at different temperatures |
| Disagrees with the CMM | Surface finish averaging; form error; temperature; the two measuring at different points |
More causes and fixes in 5 common reasons for incorrect air gage readings.
Questions about your application? Call (815) 242-0027, email info@airgaging.com, or price standard tooling online.