Question 1

How is Bonus Tolerance calculated at Maximum Material Condition (MMC)?

Accepted Answer

When the MMC modifier (Ⓜ) is specified on a feature of size, bonus tolerance is earned as the actual produced size departs from the Maximum Material Condition limit toward the Least Material Condition (LMC). For an internal hole: Bonus = D_actual - D_min. For an external shaft: Bonus = d_max - d_actual. Total allowed geometric tolerance becomes T_total = T_specified + Bonus.

Question 2

What is Virtual Condition and why is it used for functional gaging?

Accepted Answer

Virtual Condition (VC) is the constant boundary generated by the collective effect of a feature of size's Maximum Material Condition (MMC) and its stated geometric tolerance. For an internal feature (hole), VC = D_min - T_geo (the mating plug gage size). For an external feature (shaft), VC = d_max + T_geo (the mating ring gage size). If a part fits the VC gage, functional assembly is guaranteed regardless of size variations.

Question 3

How is True Position diametral deviation calculated from X and Y coordinates?

Accepted Answer

True Position is calculated by determining the radial offset from nominal basic target coordinates: r = √((X_actual - X_basic)² + (Y_actual - Y_basic)²). The actual diametral position deviation is t_actual = 2 · r = 2 · √(ΔX² + ΔY²). If t_actual ≤ T_total, the feature is conforming. A cylindrical tolerance zone provides 57.08% more allowable area than a square ± coordinate tolerance box.

Question 4

What is the difference between Worst-Case and Statistical RSS tolerance stack-ups?

Accepted Answer

Worst-Case tolerance stack-up (T_WC = Σ T_i) assumes all dimensions simultaneously reach their extreme tolerance limits in the most unfavorable direction, guaranteeing 100% interchangeability but requiring tight, expensive manufacturing tolerances. Statistical Root-Sum-Square (T_RSS = √(Σ T_i²)) assumes normal distribution (3σ) where extremes rarely coincide, yielding a tighter assembly envelope and allowing looser component tolerances.

Question 5

What is the Bender factor in tolerance stack-up analysis?

Accepted Answer

The Bender factor (T_Bender = 1.5 · T_RSS) modifies the standard RSS statistical stack by applying a 1.5x multiplier. This accounts for practical manufacturing shifts such as tool wear, thermal drift, process non-centering (mean shift), and slight non-normal distributions encountered in real-world high-volume machining.

Question 6

How does the 3-2-1 Datum Reference Frame constrain 6 degrees of freedom?

Accepted Answer

Per ASME Y14.5 and ISO 5459, the 3-2-1 rule establishes a repeatable coordinate system: the Primary Datum contacts 3 non-collinear high points to eliminate 1 translation and 2 rotations (3 DOF); the Secondary Datum contacts 2 points perpendicular to the primary to eliminate 1 translation and 1 rotation (2 DOF); the Tertiary Datum contacts 1 point to eliminate the final translation (1 DOF), locking all 6 degrees of freedom.

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