Section Views and Auxiliary Views

While standard orthographic projections (front, top, side) are sufficient for many simple objects, complex parts often have internal features or inclined surfaces that cannot be clearly detailed using only standard views and hidden lines. In these cases, engineers rely on section views and auxiliary views.

Section Views

Section views are used to reveal the internal features of an object that would normally be hidden. Over-relying on hidden (dashed) lines for complex internal geometry creates confusing drawings that can lead to misinterpretation during manufacturing.

The Concept of a Section View

Imagine taking a saw and cutting the part open along a specific plane. If you remove the front portion of the cut part and draw what remains, you have created a section view.

Key Elements of a Section View

1. Cutting-Plane Line: This thick, specialized line (often with a repeating pattern of one long and two short dashes) is drawn on a standard view to indicate exactly where the imaginary cut takes place. Arrows at the ends of the cutting-plane line point in the direction of the line of sight for the section view.
2. Section Lines (Cross-Hatching): These are thin, angled lines drawn across the solid surfaces that were "cut" by the cutting plane. They help clearly distinguish between solid material and empty space (like holes or slots).

Common Types of Section Views

• Full Section: The cutting plane passes entirely through the object, splitting it in half.
• Half Section: Used for symmetrical objects. The cutting plane only goes halfway through, removing a quarter of the part. This allows one side of the view to show the exterior and the other side to show the interior.
• Offset Section: The cutting plane is stepped (bent at 90-degree angles) to pass through internal features that do not lie in a single straight line.
• Broken-Out Section: Only a small area of a view is "broken away" to reveal internal details, without running a full cutting plane across the entire part.

Auxiliary Views

Orthographic projection works perfectly when the faces of the object are parallel to the principal projection planes. But if a part has an inclined surface, that surface will appear foreshortened (distorted) in the standard front, top, or side views.

To show the true shape and size of an inclined surface, an auxiliary view is required.

The Concept of an Auxiliary View

An auxiliary view is an orthographic projection projected onto a plane that is parallel to the inclined surface, rather than parallel to one of the six principal planes.

Because the line of sight for the auxiliary view is perfectly perpendicular to the inclined face, the resulting drawing displays the features on that face (like holes or slots) in their true geometry. This is critical because dimensioning can only be performed on views that show true shape.

Application

Auxiliary views are often drawn as partial views, showing only the inclined surface itself. Drawing the rest of the complex part from that specific angled viewpoint would add unnecessary confusion and waste drafting time.