Sure-Fit or Extreme Variability Formulae and Calculator

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Sure-Fit or Extreme Variability Formulae and Calculator

Tolerances, Engineering Design & Limits & Fits

Sure-Fit or Extreme Variability of Mechanical Tolerances Calculator

The sure-fit or extreme variability of a function of several uncorrelated random variables could be found by substituting values for the variables to find the maximum and the minimum value of the function

Preview Sure-Fit Mechanical Tolerance Design Calculator

Eq. 1
y = ( x₁ + 2 · x₂ ) / x₃³

The maximum value of y_max is given by:

Eq. 2
y_max = ( x_1,max + 2 · x_2,max ) / x³_3,min

Similarly for the minimum value:

Eq. 3
y_min = ( x_1,min + 2 · x_2,min ) / x³_3,max

The sure-fit or extreme variability can then be determined as:

Eq. 4
Δy = y_max - y_min

Approximation extreme variability.

Eq. 5
Δy = | y / x₁ | Δx₁ + | y / x₂ | Δx₂ + | y / x₃ | Δx₃

Eq. 5a
Δx₁ = x_1,max - x_1,max

Eq. 5b
Δx₂ = x_2,max - x_2,min

Eq. 5c
Δx₃ = x_3,max - x_3,min

Source:

Mechanical Design, 2nd edition
Peter R. N. Childs