GD&T Position Tolerancing Calculations 3 — Questions and Answers
Question 1: A hole is located at basic X = 40.00, Y = 30.00. The CMM measures the hole axis at X = 40.05, Y = 29.96. What is the diametral position error?
- ⌀0.064
- ⌀0.128 (Correct answer)
- ⌀0.090
- ⌀0.032
Correct answer: ⌀0.128
Δx = 0.05, Δy = 0.04; radial = √(0.0025 + 0.0016) = √0.0041 ≈ 0.064; diametral = 2 × 0.064 ≈ ⌀0.128.
Question 2: What does the term 'virtual condition' mean for an internal feature (hole) controlled with position at MMC?
- MMC size plus the position tolerance
- MMC size minus the position tolerance (Correct answer)
- LMC size plus the position tolerance
- The actual measured size of the hole
Correct answer: MMC size minus the position tolerance
For an internal feature, virtual condition = MMC size − position tolerance, representing the worst-case boundary for assembly.
Question 3: A pin (external feature) has MMC = 12.0 mm and a position tolerance of ⌀0.3. What is its virtual condition?
- 11.7 mm
- 12.3 mm (Correct answer)
- 12.0 mm
- 11.85 mm
Correct answer: 12.3 mm
For an external feature, virtual condition = MMC + position tolerance = 12.0 + 0.3 = 12.3 mm.
Question 4: Projected tolerance zone is specified because:
- It eliminates the need for datum references
- It controls the zone where a fastener extends outside the part, preventing interference at assembly (Correct answer)
- It applies the tolerance regardless of feature size
- It converts the zone from cylindrical to conical
Correct answer: It controls the zone where a fastener extends outside the part, preventing interference at assembly
A projected tolerance zone extends the positional control above the hole to where mating fasteners or studs will reside, preventing angular stack-up issues.
Question 5: If a position callout reads ⌀0.25 (M) with a projected tolerance of 15 mm, what does '15' represent?
- The diameter of the tolerance zone
- The depth of the hole
- The minimum projection height above the part surface (Correct answer)
- The number of features in the pattern
Correct answer: The minimum projection height above the part surface
The projected tolerance zone height (15 mm) specifies how far the cylindrical zone extends beyond the part surface to capture fastener axis deviation.
Question 6: A zero tolerance at MMC callout (⌀0.000 (M)) means:
- The feature must be perfect regardless of size
- The entire size tolerance becomes available as bonus position tolerance when at actual size (Correct answer)
- No positional variation is permitted at any size
- The feature must be measured at exactly MMC
Correct answer: The entire size tolerance becomes available as bonus position tolerance when at actual size
With ⌀0.000 at MMC, there is no fixed tolerance; all allowable variation comes exclusively from bonus tolerance as the feature departs from MMC.
Question 7: Which statement correctly describes the 'inner boundary' of a hole controlled with position at MMC?
- LMC size plus position tolerance
- MMC size minus position tolerance (Correct answer)
- LMC size minus position tolerance
- Actual size plus position tolerance
Correct answer: MMC size minus position tolerance
The inner boundary (worst-case minimum size) = MMC − position tolerance, which equals the virtual condition for an internal feature.
GD&T Position Tolerancing Calculations 3
A hole is located at basic X = 40.00, Y = 30.00.
The CMM measures the hole axis at X = 40.05, Y = 29.96.
What is the diametral position error?