Datum Systems & Reference Frames Flashcards

What is the primary purpose of applying the MMC modifier (M) to a datum feature reference?

Answer: To allow datum shift when the datum feature departs from MMC

When MMC is applied to a datum feature reference, bonus datum shift is permitted as the datum feature departs from its maximum material condition.

Datum shift is allowed when which modifier is applied to a datum feature of size?

Answer: Both MMC and LMC, but not RFS

Datum shift is available when either MMC or LMC is applied to a datum feature of size reference; RFS requires the datum to be derived without shift.

Which of the following is NOT a type of datum target?

Answer: Datum target volume

Datum targets are defined as points, lines, or areas; there is no 'datum target volume' in GD&T per ASME Y14.5.

In a datum reference frame, what does the term 'degrees of freedom' refer to?

Answer: The independent modes of translation and rotation of a part in space

Degrees of freedom are the six independent ways a rigid body can move in 3D space: three translations (X, Y, Z) and three rotations (u, v, w).

A movable datum target is identified on a drawing by:

Answer: Two parallel horizontal lines below the datum target symbol

A movable datum target is indicated by two parallel horizontal lines (a slide symbol) beneath the standard datum target symbol to indicate it can be repositioned.

Per ASME Y14.5, which letter is typically NOT used as a datum reference letter to avoid confusion with numbers?

Answer: I, O, Q

The letters I, O, and Q are avoided as datum reference letters because they can be confused with the numbers 1, 0, and 9 respectively.

When a flat surface is designated as the primary datum, what condition must that surface satisfy for proper datum establishment?

Answer: It must be within its specified form tolerance

The flat surface used as a primary datum must be within its specified flatness (or other applicable form) tolerance to properly contact and define the datum plane.