KEVOS® MAKEOS · Quality
Measurement Error from Part and Gauge Temperature
How far off is my measurement because the part and gauge are not at 20 °C, and what is the true size?
Size error when a part and the gauge or machine scale measuring it are at temperatures other than the 20 °C reference: the apparent deviation from their different expansions, the size corrected to 20 °C, the share of the tolerance the error uses, and the temperature difference that would keep the error within a chosen share of tolerance.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Nominal size | mm | Nominal length being measured. |
| Part expansion coefficient | µm/m·K | Expansion coefficient of the part (23 aluminium, 11.5 steel). |
| Part temperature | °C | Temperature of the part when measured. |
| Gauge or scale expansion coefficient | µm/m·K | Expansion coefficient of the gauge, scale or CMM (11.5 steel, about 0 for glass-ceramic scales). |
| Gauge temperature | °C | Temperature of the gauge or scale. |
| Measured size (0 = nominal) | mm | The reading taken (0 uses the nominal size). |
| Total tolerance band | mm | Total tolerance band of the dimension. |
| Share of tolerance allowed for temperature | % | Share of the tolerance you allow for temperature effects. |
Method and formulas
- Both expand from their 20 °C sizes: apparent deviation = L [α_p (T_p − 20) − α_g (T_g − 20)].
- Size at 20 °C = measured − deviation.
- For part and gauge at the same temperature, the error per kelvin is L |α_p − α_g|; allowable offset = share × tolerance ÷ (L |α_p − α_g|).
- Example: a 500 mm aluminium part at 28 °C measured with steel at 22 °C reads 80.5 µm large.
Limitations
- Uniform temperatures; parts straight from machining have gradients.
- Coefficients vary with alloy; use measured values for tight work.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Correct measurements taken on the shop floor
- Decide how long parts must soak before inspection
- Explain disagreements between shop and inspection measurements
Who it is for
- Quality engineers
- Tooling engineers
- Metrology technicians
What you get
- Apparent deviation from temperature
- Size corrected to 20 °C
- Share of tolerance used and allowable temperature difference
Interpreting the result
- Equal temperatures do not remove the error when part and gauge are different materials.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 375–378, 2660. Topic reference; no source tables or recommended settings are reproduced.
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