Datum Systems & Reference Frames Flashcards

In the three-plane datum reference frame, which datum plane constrains the most degrees of freedom?

Answer: Primary datum plane

The primary datum plane contacts the part at a minimum of three points and constrains three degrees of freedom (one translation and two rotations).

A datum feature simulator for a flat primary datum must be:

Answer: Nominally perfect in form

Datum feature simulators are nominally perfect counterparts of the datum feature, used to establish the datum from which measurements are taken.

When a cylindrical feature is used as a primary datum, it constrains how many degrees of freedom?

Answer: Four

A cylindrical primary datum constrains four degrees of freedom: two translations perpendicular to its axis and two rotations perpendicular to its axis.

What does the order of datum references (primary, secondary, tertiary) in a feature control frame determine?

Answer: The sequence of part setup and degree-of-freedom constraint

The order of datum references establishes the hierarchy of constraint, dictating the sequence in which the part is brought into contact with datum simulators.

A datum reference frame is established by a minimum of:

Answer: Three datum features

A complete datum reference frame typically requires three mutually perpendicular datum planes established from at least three datum features to fully constrain six degrees of freedom.

In GD&T, what is the term for the actual part surface used to establish a datum?

Answer: Datum feature

A datum feature is the actual feature on the part (surface, axis, or center plane) that contacts the datum feature simulator to establish the datum.

Which symbol in a feature control frame indicates that a datum applies at maximum material boundary?

Answer: (M)

The (M) modifier indicates Maximum Material Condition (MMC), meaning the datum applies when the datum feature contains the maximum amount of material.