Thermal expansion calculator

How it is calculated

Change in length ΔL = α × L × ΔT
Size at temperature T L_T = L₂₀ × (1 + α × (T − 20))
Apparent error when instrument and workpiece materials differ e ≒ L × (α_w × (T_w − 20) − α_s × (T_s − 20))
Loss of interference (different hole and shaft materials) Δδ = (α_hole × ΔT_hole − α_shaft × ΔT_shaft) × d
Shrink-fit temperature rise ΔT = (δ + c) ÷ (α × d)  Cold-fit shaft temperature T = room temp. − (δ + c) ÷ (α × d)

• Dimensional measurement is referenced to 20 °C (bearing and measuring-instrument makers; JIS B 0680 / ISO 1).
• Steel calipers and micrometers expand almost like steel parts, so at the same temperature the effect largely cancels. With aluminum or plastic parts it does not, and the reading comes out large.
• Holding a micrometer bare-handed warms and stretches the frame. Do not hold setting standards directly either, and leave the instrument and standard in the same place for several hours before zeroing (Mitutoyo).
• The expansion coefficient falls at low temperature, so a cold fit needs to go colder than the value calculated with the room-temperature coefficient.

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Press fit (pressure, force, shrink-fit temperature) · ISO fits · Measuring instruments