Sectional Views in Engineering Drawing

 Sectional Views in Engineering Drawing

What is Sectioning?

Sectioning is a technique used in engineering drawings to show the internal details of an object by imagining that it has been cut by a plane. The “cut” portion is then drawn as a sectional view, making it easier to visualize complex interiors without confusion.

Sectional Views and Sectional Planes

A sectional view is created by introducing an imaginary cutting plane through the object. This plane, called the sectional plane, can be vertical, horizontal, or inclined depending on what needs to be shown. The portion of the object in front of the plane is removed, and the inside details are revealed in the drawing.

Hatching: The Heart of Section Representation

Once a section is drawn, the cut areas are marked with hatching lines (also called section lines).

  • Inclination: Hatching lines are generally drawn at 45° to the main outline of the section.

  • Spacing: The spacing between lines should be uniform, typically between 1 mm to 3 mm, depending on the scale of the drawing.

  • Large Areas: For very large areas, hatching may be limited to the boundaries to avoid clutter.

  • Adjacent Parts: When two parts are next to each other, their hatching is drawn in opposite directions or with different spacing to clearly distinguish them.

Types of Sections

1. Full Section

In a full section, the cutting plane passes entirely through the object, showing the full internal structure in a single view. This is often used for symmetrical objects.

2. Half Section

In a half section, only half of the object is cut away, while the other half remains in the external view. This method is especially useful for symmetrical objects where both interior and exterior details need to be shown together.

Types of Half Sections

  • Horizontal Half Section – Cutting plane is horizontal.

  • Vertical Half Section – Cutting plane is vertical.

  • Offset Half Section – Cutting plane is bent to pass through important features.

Conventional Representation of Materials

Different materials are represented by unique hatching patterns in sectional views:

  • Cast Iron – Parallel lines at 45°

  • Steel – Alternating thick and thin lines

  • Brass – Parallel lines with intermittent short dashes

  • Wood – Grain pattern lines
     These standard patterns make it easy to identify the material of each part without lengthy notes.

Why Sectioning Matters

Sectioning isn’t just a drawing technique—it’s a vital communication tool in engineering. It:

  • Eliminates guesswork in interpreting designs

  • Reveals hidden features clearly

  • Reduces the need for multiple complex views

  • Ensures manufacturing accuracy

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