Coordinate (rectangular) dimensioning: Is a pair of mutually perpendicular datum planes required to establish the coordinate origin and axes for 2D coordinate dimensioning on a view?

Introduction / Context:Coordinate (rectangular) dimensioning locates features by their X and Y distances from established datums. To do this unambiguously on a 2D view, two mutually perpendicular datum references define the axes and origin. Understanding this setup is essential to consistent measurement and inspection practices.

Given Data / Assumptions:

• A 2D drawing view is used to define feature locations.
• Two perpendicular datums (for example, datum A and datum B) are available on that view.
• Geometric relationships rely on consistent axes from these datums.

Concept / Approach:Establishing two perpendicular datum planes (or centerlines/edges functioning as datums) defines a rectangular coordinate frame. Feature coordinates (X, Y) are then measured from the intersection, ensuring repeatability. In full 3D, a third perpendicular datum would define Z, but for a single view's 2D coordinate dimensioning, two suffice.

Step-by-Step Solution:

Verification / Alternative check:Inspection fixtures and CMM programs typically begin by establishing two (or three) mutually perpendicular datums to define coordinate axes, validating the necessity in practice.

Why Other Options Are Wrong:

Common Pitfalls:Choosing non-functional datums that drift during assembly; failing to ensure actual perpendicularity of datum features in the product design.

Final Answer:Correct