Shrink fit calculator
A shrink fit goes together hot: heat the hub until its bore grows past the shaft, ΔD = α·D·ΔT. A 50 mm H7/s6 fit has up to 59 µm of interference, so a steel hub (α about 11 µm/m·K) has to rise about 106 K before the bore just clears the shaft. Choose the fit, the material and the clearance you want at assembly to get the temperature, or cool the shaft instead.
The second mode brings a size measured on a warm or cold part back to 20 °C, the temperature drawing sizes are given at.
Looking up the limits.
How it’s calculated
ΔD = α·D·ΔT. The bore must grow past the shaft by the most interference I (es − EI) plus the clearance c, so ΔT = (I + c) ÷ (α·D), with α in µm/m·K and D in m. Heated and cooled together, each part moves by the same ΔT and their α add. The range runs from the highest published α to the lowest.
Expansion coefficients
| Material and publishers | α, µm/m·K |
|---|---|
| Carbon steel 1020Milltech Martin Bright 11.7 (0–100 °C) · Bright Steel 11.7 (20–100 °C) | 11.7 |
| Carbon steel 1045 / C45Bright Steel 11.5 (20–100 °C) · Lucefin 11.1 (20–100 °C) | 11.1–11.5 |
| Alloy steel 4140 / 42CrMo4Swiss Steel 11.1 (20–100 °C) · thyssenkrupp 11.1 (20–100 °C) · Swiss Steel 12.1 (20–200 °C) · thyssenkrupp 12.1 (20–200 °C) | 11.1–12.1 |
| Alloy steel 4340 / 34CrNiMo6Swiss Steel 11.1 (20–100 °C) · thyssenkrupp 11.1 (20–100 °C) · Lucefin 11.1 (20–100 °C) · Swiss Steel 12.1 (20–200 °C) · thyssenkrupp 12.1 (20–200 °C) | 11.1–12.1 |
| Stainless 304Atlas Steels 17.2 (0–100 °C) · Engineering ToolBox 17.3 (about 25 °C) | 17.2–17.3 |
| Stainless 316Atlas Steels 15.9 (0–100 °C) · Engineering ToolBox 16.0 (about 25 °C) | 15.9–16.0 |
| Stainless 410Atlas Steels 9.9 (0–100 °C) · Engineering ToolBox 9.9 (about 25 °C) | 9.9 |
| Aluminium 2011, 5083, 6061AZoM (2011) 23.0 (20–100 °C) · AZoM (6061) 23.2 (20–100 °C) · AZoM (5083) 23.4 (20–100 °C) · Engineering ToolBox 23.0 (about 25 °C) | 23.0–23.4 |
| Free-cutting brass C36000Copper Development Association 20.5 (20–300 °C) · Engineering ToolBox 18.0 (about 25 °C (18–19)) · Engineering ToolBox 19.0 (about 25 °C (18–19)) | 18.0–20.5 |
| Bearing bronze C93200Copper Development Association 18.0 (20–100 °C) · Engineering ToolBox 17.5 (about 25 °C (17.5–18)) · Engineering ToolBox 18.0 (about 25 °C (17.5–18)) | 17.5–18.0 |
| Copper C11000Copper Development Association 16.9 (20–100 °C) · Engineering ToolBox 16.0 (about 25 °C (16–16.7)) · Engineering ToolBox 16.7 (about 25 °C (16–16.7)) | 16.0–16.9 |
How hot does a shrink-fit hub need to be?
Hot enough that the bore grows by the fit’s largest interference plus a little clearance to slide it on: ΔT = (I + c) ÷ (α·D). The largest interference is the shaft’s upper deviation less the hole’s lower, because every pair made within the limits has to go together. Steels expand about half as much as aluminium per degree, so a steel hub needs about twice the temperature rise of an aluminium one on the same fit.
Heating can soften a quenched and tempered part once it nears the temperature it was tempered at, so the page warns for 4140 above the lowest tempering temperature its makers publish. Cooling the shaft works the same way in reverse, but the expansion coefficient falls as a metal gets colder, so a cooled shaft shrinks less than the room-temperature figure says.