GD&T Datum Reference Frames 5

Question 1

Two parts share the same datum reference frame for mating. Part A's position is called out as ⊕|Ø0.020|A|B|C. If datum B is referenced at MMC and Part A's datum B feature is at LMC, what is the maximum datum shift?

Accepted Answer

The difference between LMC and MMC of the datum B feature

Answer

Maximum datum shift occurs when the datum feature is at LMC; shift equals the full difference between LMC and MMC of the datum feature.

Question 2

What is the 'true geometric counterpart' concept as it relates to datum feature simulators?

Accepted Answer

The perfect geometric shape (plane, cylinder, etc.) that the simulator approximates

Answer

The true geometric counterpart is the perfect geometric shape that an actual datum feature simulator physically approximates to establish the datum.

Question 3

A drawing specifies a position tolerance with only one datum reference: ⊕|Ø0.015|A. What degrees of freedom remain unconstrained?

Accepted Answer

4 DOF remain unconstrained

Answer

A single planar datum A constrains only 3 DOF (1 translation + 2 rotations), leaving 3 DOF unconstrained (2 translations + 1 rotation in the datum plane).

Question 4

Which condition requires a datum feature of size to be simulated at its virtual condition boundary rather than its MMC?

Accepted Answer

When the datum feature has a straightness tolerance applied at MMC

Answer

When a form or orientation tolerance is applied to the datum feature at MMC, the datum feature simulator uses the virtual condition (MMC size ± geometric tolerance) to establish the datum.

Question 5

On a CMM inspection report, the reported 'datum A residual error' is 0.003 mm. What does this indicate?

Accepted Answer

The measured surface deviates 0.003 mm from the best-fit datum plane

Answer

Datum residual error (also called datum fit error) represents how far the actual datum feature deviates from the perfect simulator plane used to establish it.

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

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

GD&T Datum Reference Frames 5