GD&T Position Tolerancing Calculations 2 — Questions and Answers
Question 1: A hole has a position tolerance of ⌀0.4 at MMC. The actual hole diameter is 10.3 mm and MMC is 10.0 mm. What is the total allowable position tolerance?
- ⌀0.4
- ⌀0.7 (Correct answer)
- ⌀0.3
- ⌀1.0
Correct answer: ⌀0.7
At MMC the tolerance is ⌀0.4; the hole is 0.3 mm larger than MMC, so bonus tolerance adds 0.3, giving ⌀0.7 total.
Question 2: For a pattern of four holes, the True Position is defined by basic dimensions from datum A (primary), B (secondary), and C (tertiary). Which datum controls orientation of the pattern?
- Datum A (Correct answer)
- Datum B
- Datum C
- All three equally
Correct answer: Datum A
The primary datum (A) controls orientation — it establishes the first degree of constraint, typically perpendicularity or parallelism.
Question 3: A shaft pin has a position tolerance of ⌀0.5 at LMC. The actual pin diameter is 12.0 mm and LMC is 12.3 mm. What bonus tolerance is available?
- ⌀0.0
- ⌀0.3 (Correct answer)
- ⌀0.8
- ⌀0.2
Correct answer: ⌀0.3
At LMC, bonus tolerance equals the amount the actual size departs from LMC: 12.3 − 12.0 = 0.3 mm added to the stated ⌀0.5.
Question 4: The formula for converting a Cartesian position deviation (Δx, Δy) to a diametral position error is:
- Δx + Δy
- √(Δx² + Δy²)
- 2√(Δx² + Δy²) (Correct answer)
- (Δx² + Δy²)
Correct answer: 2√(Δx² + Δy²)
The diametral true-position error = 2 × √(Δx² + Δy²), because the cylindrical tolerance zone is centered on true position.
Question 5: A hole center is measured at X = 25.08 mm and Y = 15.06 mm. Basic dimensions are X = 25.00 and Y = 15.00. What is the diametral position error?
- ⌀0.14
- ⌀0.20
- ⌀0.10 (Correct answer)
- ⌀0.28
Correct answer: ⌀0.10
Δx = 0.08, Δy = 0.06; radial error = √(0.08² + 0.06²) = √(0.01) = 0.10; diametral = 2 × 0.05 = ⌀0.10.
Question 6: When RFS (Regardless of Feature Size) is applied to a position tolerance, bonus tolerance is:
- Equal to the size tolerance
- Half the size tolerance
- Not applicable — no bonus is allowed (Correct answer)
- Added automatically by the inspector
Correct answer: Not applicable — no bonus is allowed
RFS means the geometric tolerance applies at every actual feature size with no bonus; the tolerance value is fixed.
Question 7: A composite position callout has an upper segment of ⌀0.8 and a lower segment of ⌀0.2. What does the lower segment control?
- Location of the pattern from the datums
- Feature-to-feature spacing within the pattern (Correct answer)
- Orientation only, not location
- Profile of the hole surface
Correct answer: Feature-to-feature spacing within the pattern
The lower (FRTZF) segment of a composite callout controls feature-to-feature relationship (spacing/orientation) within the pattern, not its location from external datums.
GD&T Position Tolerancing Calculations 2
A hole has a position tolerance of ⌀0.4 at MMC.
The actual hole diameter is 10.3 mm and MMC is 10.0 mm.
What is the total allowable position tolerance?