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PEEK MFG

Thermal fit calculator

PEEK moves about four times more than steel per degree, and roughly three times faster again above the glass transition at 143 °C. This is the calculation behind most fits that seize or fall out when the machine warms up.

Growth per 100 mm against temperatureTg 143 °CPEEKCF30Steel20143250Temperature, °C01.02.0Growth, mm per 100 mm
Below Tg unfilled PEEK grows about 47 µm/m·K. Above it the rate nearly triples. Steel is 12 and stays straight.

How to use the answer

  • Clearance fitsIf the PEEK part sits inside metal, the clearance shrinks as things warm. Machine the cold clearance the tool reports, not the one you want hot.
  • Interference fitsA PEEK bushing pressed into steel grips harder when hot. Check the hot interference is still inside what the wall can take.
  • InspectionQuote the tolerance at a stated temperature. A 200 mm PEEK feature drifts past ±0.05 mm with a 6 °C swing in the room.
  • Above 143 °CThe tool switches to the higher coefficient for the part of the range above Tg, which is where most surprises live.

Coefficients come from the property table and are typical published values. Linear expansion only, isotropic assumption. Filled grades are anisotropic, so treat the filled results as the optimistic direction and confirm with your stock supplier.

Diameter, length or slot width. Whatever the tolerance is on.
Diametral or on the feature. Use 0 for a line to line fit, a negative value for interference.
PEEK part grows
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Mating part grows
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Differential
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Clearance at service temperature
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Machine this cold for 0.05 mm hot
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