Primary auxiliary view rule — Must a primary auxiliary view be constructed on a plane parallel to the associated inclined surface to show its true size/shape?

Introduction / Context:
Auxiliary views are created to project an inclined or skewed feature onto a plane where it appears true size and true shape. The orientation of the projection plane relative to the feature determines whether foreshortening vanishes.

Given Data / Assumptions:

• Claim: a primary auxiliary “does not need” to be parallel to the inclined plane.
• Primary auxiliary view is the first auxiliary taken directly from a principal view.
• Objective: obtain true geometry of the chosen surface/edge.

Concept / Approach:
To remove foreshortening of a plane, project it onto a plane that is parallel to it. A primary auxiliary view is constructed with the auxiliary plane parallel to the inclined surface (and perpendicular to the projection direction). If the plane is not parallel, the feature remains foreshortened and the purpose is defeated.

Step-by-Step Solution:
1) Identify the inclined surface whose true shape is required.2) Place the auxiliary plane parallel to that surface.3) Project perpendicular to the auxiliary plane to obtain true size/shape.4) Therefore the statement is false.

Verification / Alternative check:
Demonstrate with a rectangular plate inclined to the frontal plane: only when the auxiliary plane is parallel to the plate does the outline appear as a true rectangle; any other orientation yields foreshortening.

Why Other Options Are Wrong:

• Correct: Contradicts projection theory.
• Only necessary for secondary auxiliaries: Both primary and secondary follow parallelism rules to achieve true views.
• Depends on rotation angle: Rotation is chosen to achieve parallelism, not to avoid it.
• True only for cabinet oblique drawings: Oblique pictorials are unrelated to orthographic auxiliary construction.

Common Pitfalls:
Forgetting which plane must be parallel; mixing auxiliary with pictorial methods; attempting to “eyeball” true shape without establishing correct projection geometry.

Final Answer:
Incorrect