GD&T Position Tolerancing Calculations 4 — Questions and Answers
Question 1: In a 3D tolerance stack, three features contribute ±0.10, ±0.15, and ±0.20 positional deviations along the same axis. What is the worst-case total deviation?
- ±0.20
- ±0.45 (Correct answer)
- ±0.30
- ±0.25
Correct answer: ±0.45
Worst-case (arithmetic) stack = 0.10 + 0.15 + 0.20 = ±0.45 mm along that axis.
Question 2: Using RSS (Root Sum of Squares) for the same three deviations (±0.10, ±0.15, ±0.20), the statistical tolerance is approximately:
- ±0.45
- ±0.27 (Correct answer)
- ±0.35
- ±0.18
Correct answer: ±0.27
RSS = √(0.10² + 0.15² + 0.20²) = √(0.01 + 0.0225 + 0.04) = √0.0725 ≈ ±0.27 mm.
Question 3: A pattern of 6 holes must assemble with 6 clearance fasteners. MMC of holes = 10.0 mm, fastener MMC = 9.6 mm. Using the fixed fastener formula, the position tolerance is:
- ⌀0.2
- ⌀0.4 (Correct answer)
- ⌀0.8
- ⌀0.6
Correct answer: ⌀0.4
Fixed fastener tolerance = (MMC_hole − MMC_fastener) / 1 = 10.0 − 9.6 = 0.4; split between two mating parts gives ⌀0.2 each, but for a single part: ⌀0.4.
Question 4: For a floating fastener assembly, the position tolerance formula is:
- T = H − F
- T = (H − F) / 2 (Correct answer)
- T = H + F
- T = H / F
Correct answer: T = (H − F) / 2
Floating fastener formula: each part gets T = (H_MMC − F_MMC) / 2, splitting the clearance equally between both mating parts.
Question 5: A true position callout without any modifier defaults to which condition under ASME Y14.5-2018?
- MMC
- LMC
- RFS (Correct answer)
- Projected
Correct answer: RFS
Under ASME Y14.5-2018, RFS is the default implied condition when no modifier symbol (M or L) is shown.
Question 6: A position tolerance is given as ⌀0.5 with datum B at MMC. If datum feature B (a pin) measures 14.8 mm and its MMC is 15.0 mm, what is the datum shift available?
- 0.0 mm
- 0.1 mm
- 0.2 mm (Correct answer)
- 0.4 mm
Correct answer: 0.2 mm
Datum shift = MMC_datum − actual_datum = 15.0 − 14.8 = 0.2 mm, which may be used to relax the positional requirement.
Question 7: A bolt circle of 8 holes equally spaced on a ⌀100 mm bolt circle has a position tolerance of ⌀0.3. What basic angular spacing is used between adjacent holes?
- 30°
- 45° (Correct answer)
- 40°
- 60°
Correct answer: 45°
360° ÷ 8 holes = 45° basic angular spacing between each adjacent hole on the bolt circle.
GD&T Position Tolerancing Calculations 4
In a 3D tolerance stack, three features contribute ±0.10, ±0.15, and ±0.20 positional deviations along the same axis.
What is the worst-case total deviation?