GD&T Material Condition Modifiers 3 — Questions and Answers
Question 1: The term 'resultant condition' for an internal feature controlled at MMC refers to:
- The worst-case inner boundary considering both size and geometric tolerance (Correct answer)
- The worst-case outer boundary considering both size and geometric tolerance
- The virtual condition boundary
- The boundary at RFS
Correct answer: The worst-case inner boundary considering both size and geometric tolerance
The resultant condition of an internal feature at MMC is the worst-case inner boundary = LMC size minus the maximum allowable tolerance.
Question 2: Which of the following GD&T tolerances is most commonly applied with an MMC modifier to take advantage of bonus tolerance for assembly purposes?
- Flatness
- Circularity
- True Position (Correct answer)
- Profile of a Surface
Correct answer: True Position
True position is most commonly modified with MMC because assembly clearance naturally increases when mating features depart from MMC.
Question 3: An LMC modifier is most useful for controlling which engineering concern?
- Maximum interference in press-fit assemblies
- Minimum wall thickness and edge distance (Correct answer)
- Maximum bonus tolerance for assemblies
- Datum feature shift for clearance fits
Correct answer: Minimum wall thickness and edge distance
LMC ensures minimum material (wall thickness, edge distance) is maintained, making it useful for structural or sealing concerns.
Question 4: A pin (external feature) has a size range of 9.9–10.0 mm. At MMC, the straightness tolerance is 0.05 mm. What is the maximum allowable straightness tolerance when the pin measures 9.9 mm?
- 0.05 mm
- 0.10 mm
- 0.15 mm (Correct answer)
- 0.20 mm
Correct answer: 0.15 mm
At 9.9 mm (LMC), departure from MMC is 0.1 mm; adding this bonus to 0.05 mm gives 0.15 mm total.
Question 5: Which boundary is established by the MMC size of an external feature PLUS its applicable geometric tolerance?
- Inner boundary
- Outer boundary / Virtual condition (Correct answer)
- Resultant condition
- Envelope principle boundary
Correct answer: Outer boundary / Virtual condition
For an external feature at MMC, the virtual condition (worst-case outer boundary) equals MMC size plus the geometric tolerance.
Question 6: When an MMC modifier is applied to a tolerance of flatness, what happens?
- Bonus tolerance is granted as the feature departs from MMC
- The flatness zone expands but remains independent of size
- It is invalid — flatness cannot use MMC (Correct answer)
- The feature must be measured at MMC only
Correct answer: It is invalid — flatness cannot use MMC
Flatness is a surface form control that does not reference feature size, so applying MMC to flatness is not allowed per ASME Y14.5.
Question 7: Datum shift is analogous to bonus tolerance. Which statement correctly describes datum shift?
- It is additional tolerance given to the controlled feature
- It is the allowable movement of the true datum axis/plane due to the datum feature's departure from its referenced material condition (Correct answer)
- It changes the MMC of the datum feature
- It only applies when the datum is at RFS
Correct answer: It is the allowable movement of the true datum axis/plane due to the datum feature's departure from its referenced material condition
Datum shift is the permissible translation/rotation of the datum reference frame that occurs when the datum feature departs from its referenced material condition.
GD&T Material Condition Modifiers 3
The term 'resultant condition' for an internal feature controlled at MMC refers to: