Form and Orientation Tolerances Flashcards

Which GD&T symbol is used to control the straightness of a surface element (line element) on a cylindrical part?

Answer: Straightness (⏤)

Straightness controls individual line elements on a surface or the derived median line of a feature of size.

A flatness tolerance zone is defined as the space between two:

Answer: Parallel planes

Flatness tolerance zone consists of two parallel planes within which the entire surface must lie.

When angularity is applied to a surface, what is the shape of the tolerance zone?

Answer: Two parallel planes at the specified angle to the datum

Angularity applied to a surface creates a tolerance zone of two parallel planes oriented at the specified angle relative to the datum.

Cylindricity differs from circularity in that cylindricity controls:

Answer: Both the roundness and straightness of the entire surface simultaneously

Cylindricity simultaneously controls circularity, straightness, and taper of the entire cylindrical surface in a single tolerance.

Which statement about form tolerances and datums is correct?

Answer: Form tolerances never reference datums

Form tolerances (flatness, straightness, circularity, cylindricity) by definition control the shape of an individual feature and never require datum references.

A perpendicularity callout on a pin's axis controls the orientation of the pin's derived median line relative to:

Answer: A referenced datum plane or axis

Perpendicularity applied to an axis controls how closely the feature's derived median line is 90° to the referenced datum.

Under ASME Y14.5, the circularity (roundness) tolerance value must be:

Answer: Less than or equal to the size tolerance

Per Rule #1 (Envelope Principle), the circularity tolerance cannot exceed the size tolerance because the feature must remain within its size limits.

What does it mean when a straightness tolerance is applied to the derived median line of a shaft rather than its surface?

Answer: Rule #1 is overridden and the shaft axis may bow outside the MMC boundary

Straightness of the derived median line overrides Rule #1, allowing the axis to bend outside the perfect-form-at-MMC boundary while the shaft remains within size limits at each cross-section.

A parallelism tolerance of 0.05 mm applied to a surface means the surface must lie between two planes that are parallel to the datum and separated by:

Answer: 0.05 mm

The tolerance value of 0.05 mm directly defines the width of the tolerance zone between the two parallel planes.

Which orientation tolerance would you use to ensure a drilled hole is exactly 90° to a datum surface?

Answer: Perpendicularity

Perpendicularity is the orientation tolerance specifically defined for 90° relationships between a feature and a datum.

On a GD&T drawing, a circularity tolerance of 0.02 applied to a sphere means:

Answer: Every cross-section through the center must have a roundness within 0.02

Circularity on a sphere requires every cross-section passing through the center to be circular within the tolerance value.

Which of the following best describes the cylindricity tolerance zone?

Answer: Two coaxial cylinders between which the surface must lie

Cylindricity's tolerance zone consists of two coaxial (same-axis) cylinders; the entire surface must fall between them.

An angularity tolerance applied to a hole axis at 45° to a datum controls the hole axis within a:

Answer: Cylindrical zone oriented at 45° to the datum

When angularity is applied to an axis (feature of size), the tolerance zone is a cylinder oriented at the specified angle to the datum.

What is the primary difference between flatness and parallelism?

Answer: Parallelism requires a datum reference; flatness does not

Flatness controls a surface's form independently with no datum, while parallelism controls a surface's orientation relative to a referenced datum.

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:

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.

Which GD&T control is most appropriate to ensure two mating flat surfaces will make full contact (not rock)?

Answer: Flatness

Flatness controls how planar a single surface is, preventing rocking or wobble when two surfaces are mated.

Under ASME Y14.5-2018, which modifier can be applied to straightness of a derived median line to allow additional tolerance?

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.

A parallelism callout of 0.1 on a surface with datum A means the surface must:

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.

When a perpendicularity tolerance is applied to a flat surface (not an axis), which modifier is NOT applicable?

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.

A cylindricity tolerance of 0.03 mm means the entire cylindrical surface must fit between two coaxial cylinders whose radii differ by:

Answer: 0.03 mm

The cylindricity tolerance value of 0.03 mm equals the total radial difference between the two coaxial boundary cylinders.