The starting question
At what temperature is the dimension defined, and what changes when the part is in service?
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The parts, photos or measurements you already have.
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How the pieces connect, move and leave room for access.
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Which interfaces must stay fixed, and what can change?
Start with the temperature of the dimension
Record the temperature associated with the initial dimension and the temperatures expected in service. Do not compare dimensions measured in different conditions without identifying that difference.
A dimension defined at one condition is not automatically the size of a warm or cold part. Explain whether your question concerns one free part, two mating parts, or a constrained assembly.
Use a coefficient with its range and units
A mean coefficient belongs to a stated temperature interval and a particular product or material condition. A mean over a broad interval is not automatically the mean for a smaller interval inside it. Keep its units beside it. A value in ppm per Fahrenheit degree cannot be entered unchanged into a field expecting ppm per Celsius degree.
Alleima lists a metric mean linear coefficient of 16.5 ×10⁻⁶/°C for Sanmac 304/304L over 30–100 °C. For an illustrative 100 mm reference length at 30 °C, the constant-mean model gives 100 ×16.5 ×10⁻⁶ ×70 =0.1155 mm growth at 100 °C. This reference does not cover every stainless grade or temperature interval.
Separate dimension change from assembly behavior
A free-expansion calculation does not determine contact force, stress, distortion or whether an assembly will function. Restraint and temperature gradients can change the problem. A source coefficient alone does not resolve those questions.
For polymers, identify the exact grade, processing direction and temperature interval. Manufacturer guidance shows that expansion can depend on direction and can change across a glass transition. Use applicable producer data rather than one generic plastic coefficient.
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Your working checklist
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References & further reading
- Alleima — Sanmac 304/304L physical properties ↗
- NIST — Uncertainty and Dimensional Calibrations ↗
- Victrex — product property guide, thermal expansion ↗
References support the named topic; they do not certify a design, setup or product.
Planning guidance and illustrative examples. Confirm project-specific requirements with the responsible design, manufacturing and quality teams.
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