Interference fit — probability of falling short of a target

Probability that the actual (normally-distributed) interference of a hole/shaft fit falls below a chosen minimum threshold, from the hole and shaft tolerance bands.

✓ validated against legacyoriginal: /calculators/H7r6.htm

Bore deviation, minimum, HₘᵢₙµmBore deviation, maximum, HₘₐₓµmShaft deviation, minimum, sₘᵢₙµmShaft deviation, maximum, sₘₐₓµmMinimum required interference, δ₁µm

Interference, worst-case minimum7 µm

Interference, worst-case maximum41 µm

Mean interference24 µm

Standard deviation, interference4.12 µm

Exceedance probability, F(t)50.02 %

Method & references

Normal distribution of hole and shaft tolerances, combined by error propagation into a single interference distribution.
F(t) is the one-sided probability that the actual interference falls below the given minimum required value.
Example (20H7/r6) — complements the press-fit tolerance calculator, which goes the other direction: probability in, interference bounds out.

The computation is a literal port of the original client-side JavaScript from /calculators/H7r6.htm. Results are verified equal to the original by an automated golden-master test. No formula has been re-derived or “improved”.

Interference fit — probability of falling short of a target — Engineering ABC