Section Views and Auxiliary Views

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

Section Views

A section view is used to expose the internal features of an object that would otherwise be hidden. Relying heavily on hidden lines for complex internal geometries can make a drawing confusing and prone to misinterpretation during manufacturing.

Concept of a Section View

Imagine taking a saw and cutting a 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 pattern of long and double short dashes) is placed on a standard view to indicate exactly where the imaginary cut is made. Arrowheads 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): Thin, angled lines drawn across the solid surfaces that were "cut" by the cutting plane. These lines clearly distinguish the solid material from empty space (like holes or slots).

Common Types of Section Views

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

Auxiliary Views

Orthographic projection works perfectly when the faces of the object are parallel to the principal projection planes. However, if a part has an inclined or slanted 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.

Concept of an Auxiliary View

An auxiliary view is an orthographic view 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 exactly perpendicular to the inclined face, the resulting drawing shows the features on that face (such as holes or slots) in their true geometry. This is critical because dimensions can only be applied to true-shape views.

Application

Auxiliary views are often drawn as partial views, showing only the inclined surface itself, as drawing the rest of the complex part from that specific angle would be unnecessarily confusing and time-consuming.