Why and when to use auxiliary views What is the principal reason for creating an auxiliary view in technical drawing when a surface is inclined in a primary orthographic view?

Introduction / Context:
Orthographic projections represent 3D geometry via 2D views (front, top, right). Surfaces inclined to these principal planes appear foreshortened, which complicates dimensioning and shape interpretation. Auxiliary views solve this by projecting onto a plane oriented perpendicular to the inclined surface’s normal direction.

Given Data / Assumptions:

• A surface is inclined in a primary view (not parallel to any principal plane).
• The designer needs a view where that surface shows true size and shape.
• Standard descriptive geometry procedures are used.

Concept / Approach:
An auxiliary view is constructed by projecting geometry onto a plane that is perpendicular to the surface’s normal, making the surface appear in true size. This enables accurate dimensioning of edge lengths, hole patterns, and cut angles. While eliminating hidden lines can be a side effect, it is not the main purpose. Showing cylinders as ellipses occurs naturally in certain views but is not the goal of an auxiliary view.

Step-by-Step Solution:

Verification / Alternative check:
Measure a known edge on the inclined surface: it is shorter in the principal view but matches its true length in the auxiliary, confirming correct construction and enabling precise dimensioning.

Why Other Options Are Wrong:

• Eliminate hidden lines: not the primary reason, merely a potential benefit.
• Show cylinders as ellipses: descriptive effect, not the purpose.
• Locate center marks: handled within any view; not why an auxiliary is created.

Common Pitfalls:

• Dimensioning on foreshortened views, causing manufacturing errors.
• Incorrect auxiliary plane orientation, leading to partial foreshortening.

Final Answer:
to create a true projection plane from an inclined plane in one of the primary views