What is a sectional hatching pattern, and how is it used?

Short Answer:

A sectional hatching pattern is a group of thin, parallel lines drawn at an angle inside the cut area of a part in a sectional view of an engineering drawing. These lines show the solid material that is cut through when a part is sliced to reveal its internal structure.

Hatching is used in sectional drawings to help clearly identify which areas are solid and which are empty or hollow. Different materials can also have specific hatching styles. This helps in understanding the inner construction, fitment of parts, and how they relate inside assemblies.

Detailed Explanation:

Sectional Hatching Pattern and Its Application

In mechanical engineering drawings, sometimes the external views of a component are not enough to show how the inside of the object looks. To solve this, engineers use sectional views, which represent the object as if it is cut open. This helps show internal features like holes, ribs, cavities, or walls.

To make the cut areas stand out clearly, engineers use sectional hatching patterns, also known as cross-hatching. It gives a clear indication of solid material and helps avoid confusion when reading technical drawings.

What Is a Sectional Hatching Pattern

A sectional hatching pattern consists of closely spaced, thin, parallel lines, usually drawn at a 45° angle to the horizontal. These lines are drawn only on the areas that have been cut by the imaginary section plane. This pattern visually separates solid material from empty spaces, holes, or gaps in the component.

In CAD software like AutoCAD or SolidWorks, hatching is automatically applied using built-in tools, but it follows standard rules defined by ISO or ANSI.

How It Is Used in Engineering Drawings

  1. Creating a Sectional View
    • First, a part is imagined to be cut along a plane, either vertically or horizontally.
    • The part of the object that lies in front of the cut plane is removed from view.
  2. Applying Hatching
    • The exposed surfaces after the cut are filled with hatching lines.
    • The hatching is always uniform, with lines equally spaced and angled at 45°.
    • For adjacent parts in assemblies, hatching is done at opposite or different angles to distinguish them.
  3. Types of Sectional Views Where Hatching is Used
    • Full Section: Half of the object is removed.
    • Half Section: Only one quarter is removed to show both internal and external views.
    • Offset Section: Cut follows multiple planes to show features not aligned.
    • Broken-Out Section: Small cut-out area is hatched without full section view.

Rules and Conventions for Hatching

  • Do not hatch hidden lines or holes.
  • Avoid crossing dimension lines with hatching.
  • Use lighter line weight than the object lines.
  • Do not hatch standard parts like bolts, nuts, bearings in assembly drawings.
  • Spacing of hatching lines should be uniform, generally around 2 to 4 mm apart.
  • Angle is mostly 45°, but can be 30° or 60° to distinguish different materials or parts.

Different Materials and Patterns

Sometimes, different hatching styles are used to represent different materials. For example:

  • Steel may have straight diagonal lines.
  • Aluminum may use a dot and dash pattern.
  • Wood may show grain direction.
  • These patterns help in material identification directly from the drawing.

In standard practice, however, general-purpose hatching is used unless specific material information is required.

Benefits of Using Hatching in Drawings

  1. Clarifies the Internal Shape
    • Shows what is solid and what is hollow.
  2. Improves Readability
    • Makes the drawing easier to understand even for non-engineers.
  3. Supports Manufacturing
    • Machinists understand which areas are solid and need cutting or drilling.
  4. Distinguishes Different Parts in Assemblies
    • Each part can be hatched differently for clear separation.
  5. Saves Space
    • A sectional view with hatching can replace multiple external and internal views.
Conclusion

A sectional hatching pattern is a simple but powerful way to show cut solid areas in a sectional view of an engineering drawing. It helps to clearly display internal features, improves communication with manufacturers, and adds clarity to complex designs. Following standard hatching rules ensures that drawings are professional, easy to read, and globally accepted in mechanical design and production.