3DPrintCalcs
Press Fit Calculator — Interference Fit Dimensions
Determine interference fit dimensions for inserting bearings or bushings.
How We Calculate This
Press Fit Calculations
- Realised hole = Insert diameter − Target interference (the hole MUST end up smaller than the insert)
- Design hole (draw this in CAD) = Realised hole + Hole-shrink compensation
- Effective interference = Target interference for the insert type (bearing 0.05, bushing/heat-set 0.10, magnet 0.05, pin 0.08 mm)
- Min wall = max(2 mm, Insert diameter × 0.3)
- Insertion force = P × π × d × L × μ, with contact pressure P from the Lamé thick-wall cylinder equation (P = E·δ / (d·((1+k²)/(1−k²) + ν)))
FDM holes print undersize, which on its own would make a press fit too tight. To get a repeatable fit you measure that shrink once on a calibration print and the calculator draws the CAD hole slightly larger so the printed hole lands on the target. The realised hole is always smaller than the insert — that interference is what grips the part. Heat-set inserts are the exception: the boss recess is sized a touch under the insert OD and the heated insert melts the plastic to lock in.
Frequently Asked Questions
A press fit means the hole is slightly smaller than the insert, so the insert must be pressed in with force. The interference between the parts creates friction that holds the insert in place without glue.
For bearings in PLA, 0.03-0.08mm interference works well; bushings tolerate ~0.10mm. Too much interference can crack the printed part by hoop stress, so start conservative and test. Note FDM holes print undersize, so the design (CAD) hole is drawn slightly larger to cancel that shrink — set the Hole Shrink Compensation to your measured value so the printed hole lands on the target interference rather than ending up over-tight.
Heat-set threaded inserts are generally the best solution for 3D printed threads. They melt into the plastic using a soldering iron, creating a very strong bond. They resist pull-out much better than printed or tapped threads.
Minimum 30% of the insert diameter, with an absolute minimum of 2mm. Thin walls will crack or deform during insertion. For high loads, increase to 50% of insert diameter.
Related Calculators
Bearing Calculator
Calculate bearing seat dimensions and tolerances for standard bearings.
Snap Fit Calculator
Calculate cantilever snap fit dimensions for secure clip connections.
Thread Calculator
Calculate metric thread dimensions for 3D printed bolts and threaded holes.
Gear Calculator
Design spur gears with correct module, tooth count and pitch circle dimensions.
Hinge Calculator
Design print-in-place hinges with correct clearance and pin dimensions.
Was this calculator helpful?
Last updated: February 2026
All calculations are estimates. Always verify settings with test prints before committing to final prints.