Presets
Playback
Press and fit
The ram force is hand torque divided by the pinion radius, times the efficiency. The fit resists with friction times the contact pressure over the contact area.
Model checks
The science
What is modelled
A lever arm turns a pinion that drives a rack (the ram). The ram pushes a steel shaft into a steel hub with a diametral interference; the thick-wall (Lame) contact pressure sets the friction force that grows with the inserted length.
Equations
- Ram force
F = F_hand L eta / r_pinion. - Contact pressure
p = E (delta/d)(1 - d^2/D^2) / 2for equal steel parts. - Press force
F_press = mu p pi d xat inserted length x. - Hub bore hoop stress
p (D^2 + d^2) / (D^2 - d^2).
Checks run in the page
- Lever and rack gain.
- Lame pressure from bore growth plus shaft shrinkage.
- Energy balance through the lever.
- Radial equilibrium of the hub stresses.
Honest simplifications
Plane-stress Lame model with equal moduli, a constant friction coefficient and no chamfer, lubrication, surface roughness or frame deflection. Not a design tool for real press fits.
What to try
- Press Too tight: the force line rises above the ram force and the press stalls.
- Press Long lever: a longer arm and smaller pinion lift the available force.
- Raise the hub diameter and watch the hoop stress fall.