GD&T Material Condition Modifiers 5 — Questions and Answers
Question 1: Which statement correctly compares the virtual condition of a hole controlled at MMC versus the same hole controlled at LMC?
- Both virtual conditions produce the same boundary size
- The MMC virtual condition is a smaller (tighter) inner boundary than the LMC virtual condition (Correct answer)
- The LMC virtual condition is a smaller inner boundary than the MMC virtual condition
- Virtual condition only applies at MMC, not LMC
Correct answer: The MMC virtual condition is a smaller (tighter) inner boundary than the LMC virtual condition
For a hole at MMC, virtual condition = MMC size − tolerance (smallest inner boundary); at LMC, resultant condition uses LMC − max tolerance, but virtual condition at LMC = LMC + tolerance (largest outer boundary), serving a different purpose.
Question 2: A position tolerance is given as 0.0 Ⓜ in a feature control frame. What does this indicate?
- The feature must be in perfect position at all times
- No positional error is allowed unless the feature departs from MMC, then bonus tolerance becomes available (Correct answer)
- The tolerance is invalid and must be rejected
- RFS is implied because the tolerance is zero
Correct answer: No positional error is allowed unless the feature departs from MMC, then bonus tolerance becomes available
A zero MMC tolerance means perfect position at MMC, but bonus tolerance accumulates as the feature departs from MMC, allowing positional error proportional to size departure.
Question 3: Under ASME Y14.5, which of the following tolerances CAN be legally modified with LMC?
- Flatness
- Circularity (Roundness)
- True Position of a hole (Correct answer)
- Parallelism of a surface
Correct answer: True Position of a hole
True position references a feature of size (the hole), so LMC is applicable; surface-only controls like flatness, circularity, and surface parallelism cannot use material condition modifiers.
Question 4: When inspecting a feature using a functional (hard) gauge designed for an MMC position callout, a part that passes the gauge is considered:
- Acceptable for all geometric requirements
- Acceptable for the virtual condition boundary requirement only; size still needs separate verification (Correct answer)
- Rejected because gauges only identify non-conformance
- Acceptable without needing to check actual mating size
Correct answer: Acceptable for the virtual condition boundary requirement only; size still needs separate verification
A functional gauge verifies the virtual condition (worst-case boundary) but does not verify the size tolerance, which requires a separate attribute or variable measurement.
Question 5: An engineer wants to ensure a minimum edge distance is maintained as a hole's position shifts. Which modifier applied to the position tolerance would best protect edge distance?
- MMC — maximizes bonus when the hole is largest
- LMC — provides tighter positional control when the hole is at its largest (least material) (Correct answer)
- RFS — keeps the tolerance constant regardless of size
- Free State — measures the part unconstrained
Correct answer: LMC — provides tighter positional control when the hole is at its largest (least material)
LMC tightens position control as the hole grows larger (less edge material), protecting minimum edge distance at the worst-case scenario.
Question 6: A datum feature of size is referenced as 'A Ⓜ' in a feature control frame. The datum feature has a size tolerance of 12.0–12.4 mm and is produced at 12.2 mm. How much datum shift is available?
- 0 mm
- 0.2 mm (Correct answer)
- 0.4 mm
- 0.6 mm
Correct answer: 0.2 mm
Datum shift = departure from MMC = actual size (12.2) − MMC (12.0) = 0.2 mm for this external datum feature.
Question 7: Which of the following best describes the 'inner boundary' of an internal feature (hole)?
- The largest perfect cylinder that will fit inside the hole
- The smallest permissible boundary, considering both size and geometric tolerance (Correct answer)
- The MMC size of the hole
- The virtual condition of the hole at MMC
Correct answer: The smallest permissible boundary, considering both size and geometric tolerance
The inner boundary is the most restrictive (smallest) envelope a perfect counterpart must clear, accounting for both minimum size and maximum geometric error.
GD&T Material Condition Modifiers 5
Which statement correctly compares the virtual condition of a hole controlled at MMC versus the same hole controlled at LMC?