Datum Systems & Reference Frames Flashcards
7 cards from real GD&T practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Datum Systems & Reference Frames flashcards as text
Datum targets are used primarily when:
Answer: The datum feature surface is irregular, large, or warped
Datum targets (points, lines, or areas) are used when full-surface contact is impractical due to surface irregularities, large surfaces, or casting/forging conditions.
A datum target point is represented on a drawing by:
Answer: A circle divided horizontally with an X
A datum target point is shown as a circle divided by a horizontal line, with an X in the lower half and the datum target identification in the upper half.
What does it mean when a datum reference is labeled with [CF] (Continuous Feature)?
Answer: Two or more interrupted features are treated as one datum feature
The [CF] modifier indicates that two or more separated (interrupted) features are treated as a single, continuous datum feature for establishing the datum.
In a datum reference frame, the tertiary datum plane is established by a minimum of how many points of contact?
Answer: One
The tertiary datum plane requires a minimum of one point of contact because it only needs to constrain one remaining translational degree of freedom.
Which statement best describes a 'customized datum reference frame'?
Answer: A DRF where specific degrees of freedom are selectively constrained by each datum
A customized DRF (per ASME Y14.5-2018) allows specific translational and rotational degrees of freedom to be selectively assigned to each datum reference using bracketed letter codes.
When [BSC] (Basic) appears after a datum reference in a feature control frame, it means:
Answer: The datum feature simulator is at its basic (true) size
The [BSC] modifier indicates the datum feature simulator is held at the basic (nominal) size rather than adjusting to the actual mating size of the feature.
A primary datum feature that is an external cylinder contacts its simulator at:
Answer: The minimum circumscribed cylinder (outer surface)
An external cylindrical datum feature is simulated by the minimum circumscribed cylinder that perfectly contacts the high points of the external surface.