GD&T Datum Reference Frames 4

Question 1

In the 3-2-1 locating principle, which datum provides the 3-point contact?

Accepted Answer

Primary datum

Answer

The primary datum provides 3-point minimum contact, constraining 3 degrees of freedom (1 translation + 2 rotations).

Question 2

A shaft diameter is called out as a secondary datum at MMC (⊕). As the shaft is produced 0.010 smaller than MMC, the datum shift available is:

Accepted Answer

0.010

Answer

Datum shift equals the difference between the actual mating size and MMC; if the shaft is 0.010 under MMC, shift = 0.010.

Question 3

What is the purpose of using multiple datum targets (e.g., A1, A2, A3) to establish a single datum plane?

Accepted Answer

To simulate a datum plane on a non-flat or flexible surface using discrete contact points

Answer

Multiple datum targets simulate a plane on irregular surfaces (like castings) by defining exact contact points rather than relying on full surface contact.

Question 4

Which ASME Y14.5 standard section governs datum reference frames and datum feature selection?

Accepted Answer

Section 4 — Datum Reference Frames

Answer

ASME Y14.5 Section 4 specifically covers datum reference frames, datum features, datum feature simulators, and related concepts.

Question 5

A feature control frame reads: ⊕ | Ø0.010 | A | B(M) | C. What does the (M) modifier after B indicate?

Accepted Answer

Datum B is a maximum material condition datum feature reference

Answer

The MMC modifier (M) after a datum letter means datum shift is permitted as datum B departs from its maximum material condition.

(GD&T) Geometric Dimensioning and Tolerancing Certification Practice Test

(GD&T) Geometric Dimensioning and Tolerancing Certification Practice Test

GD&T Datum Reference Frames 4