GD&T Form and Orientation Tolerances 4 — Questions and Answers
Question 1: A feature control frame shows perpendicularity with an MMC modifier (Ⓜ) applied to a pin. As the pin's actual size departs from MMC, the perpendicularity tolerance:
- Decreases by the same amount
- Remains fixed
- Increases by the same amount as the departure (Correct answer)
- Doubles
Correct answer: Increases by the same amount as the departure
The MMC modifier creates a bonus tolerance: for each unit the pin departs from MMC toward LMC, the perpendicularity tolerance increases by one unit.
Question 2: Which GD&T control is most appropriate to ensure two mating flat surfaces will make full contact (not rock)?
- Parallelism
- Flatness (Correct answer)
- Straightness
- Profile of a Surface
Correct answer: Flatness
Flatness controls how planar a single surface is, preventing rocking or wobble when two surfaces are mated.
Question 3: Under ASME Y14.5-2018, which modifier can be applied to straightness of a derived median line to allow additional tolerance?
- Least Material Condition (LMC) only
- Maximum Material Condition (MMC) or Least Material Condition (LMC) (Correct answer)
- Free State (F) only
- Projected Tolerance Zone (P) only
Correct answer: Maximum Material Condition (MMC) or Least Material Condition (LMC)
Straightness of a derived median line may use MMC or LMC modifiers to grant bonus tolerance as the feature departs from the specified material condition.
Question 4: A parallelism callout of 0.1 on a surface with datum A means the surface must:
- Be within 0.1 of the nominal distance from datum A
- Lie between two planes 0.1 apart and parallel to datum A (Correct answer)
- Not deviate from datum A by more than ±0.1
- Be flat within 0.1
Correct answer: Lie between two planes 0.1 apart and parallel to datum A
Parallelism creates a tolerance zone of two parallel planes separated by the tolerance value, both parallel to the referenced datum.
Question 5: When a perpendicularity tolerance is applied to a flat surface (not an axis), which modifier is NOT applicable?
- Free State (F)
- Maximum Material Condition (MMC) (Correct answer)
- Projected Tolerance Zone (P)
- All of the above are not applicable
Correct answer: Maximum Material Condition (MMC)
MMC and LMC modifiers apply only to features of size (axes or center planes), not to surfaces; perpendicularity on a flat surface cannot use MMC.
Question 6: A cylindricity tolerance of 0.03 mm means the entire cylindrical surface must fit between two coaxial cylinders whose radii differ by:
- 0.06 mm
- 0.015 mm
- 0.03 mm (Correct answer)
- 0.03 mm per side (0.06 total)
Correct answer: 0.03 mm
The cylindricity tolerance value of 0.03 mm equals the total radial difference between the two coaxial boundary cylinders.
Question 7: Which scenario correctly describes an angularity tolerance application?
- A surface must be perpendicular to datum B within 0.05
- A surface must be parallel to datum A within 0.05
- A surface must be at 30° to datum C within a 0.05-wide zone (Correct answer)
- A surface must be coplanar with datum D within 0.05
Correct answer: A surface must be at 30° to datum C within a 0.05-wide zone
Angularity controls a feature at a specified angle (other than 0° or 90°) to a datum, with the tolerance zone parallel to that angle.
GD&T Form and Orientation Tolerances 4
A feature control frame shows perpendicularity with an MMC modifier (Ⓜ) applied to a pin.
As the pin's actual size departs from MMC, the perpendicularity tolerance: