Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Identify and draw different types of cutting planes.
• Create sectional views of simple components according to SANS 10111.
• Interpret sectional views to understand internal features.
• Assemble simple components in 2D from various drawings.
• Apply hatching conventions correctly for different materials.

Lesson summary

This week, we delve into the crucial topic of sectional views and simple assemblies. Sectional views are vital tools in engineering drawings, allowing us to see the internal details of an object that would otherwise be hidden. Think of it like cutting an object in half to reveal its inner workings. This is incredibly important in manufacturing, construction, and maintenance because it eliminates guesswork and ambiguity. Imagine a technician trying to repair a faulty pump in a Gauteng gold mine – without a sectional view, they'd be fumbling in the dark! Simple assemblies, on the other hand, involve putting together multiple components based on an engineering drawing.

Lesson notes

2.1 Sectional Views: Revealing the Inside Sectional views are orthographic projections of an object after an imaginary cutting plane has been passed through it. They're used to show internal details that are hidden in regular views.

Types of Sectional Views: Full Section: The cutting plane passes entirely through the object. One half of the object is conceptually removed, exposing the internal features. The cutting plane is usually indicated by a chain-thin line with bold ends labeled with letters (e.g., A-A). Arrows at the ends of the line indicate the direction of sight.

Half Section: The cutting plane extends halfway through the object. This type of section is used primarily for symmetrical objects. It shows both internal and external features in the same view. One quarter of the object is removed.

Offset Section: The cutting plane is bent or offset to pass through features that are not in a straight line. This allows you to show multiple internal features in a single sectional view.

Local or Broken-out Section: A small portion of the object is broken away to reveal a specific internal detail. This is useful when you only need to show a small area of the interior.

Cutting Plane Lines and Arrows: The cutting plane line is a crucial element. It's a chain-thin line with thick ends and arrows indicating the direction of sight. The arrows show which part of the object is being "looked at" after the imaginary cut. The cutting plane line is labeled with letters to correspond to the sectional view (e.g., Section A-A).

Hatching (Section Lining): Hatching, also known as section lining, represents the material that has been cut by the cutting plane. It consists of thin, parallel lines drawn at an angle (usually 45 degrees) to the horizontal. The spacing between the lines should be uniform. Different materials are represented by different hatching symbols.

For example: Steel: Regular, evenly spaced lines.

Cast Iron: Same as steel, but with slightly thicker lines. Bronze, Brass, Copper: Different angles or spacing of lines (refer to SANS 10111). For adjacent parts, the hatching direction should be reversed or the spacing altered to clearly differentiate them.

Important: Ribs, webs, spokes, and similar features are generally not hatched when the cutting plane passes along their length. This is because they are structural elements and hatching them would make the drawing misleading.* Example 1: Full Section of a Bearing Housing Imagine a bearing housing used in a pump at a sugar mill in KwaZulu-Natal. A full sectional view would show the internal shape of the housing, the dimensions of the bearing seat, and any lubrication channels.

Orthographic Projection: Start with a front view orthographic projection of the bearing housing. Indicate the cutting plane line A-A passing through the center.

Sectional View: Draw a new front view showing the housing as if it were cut along the cutting plane A-

A. Hatching: Hatch the areas where the cutting plane has passed through solid material (the body of the housing). Ensure the hatching is consistent and at a 45-degree angle. Don't hatch the bearing itself (if shown inside) or any threaded holes if the cutting plane passes along the axis of the thread.

Labeling: Label the sectional view "Section A-A".

Example 2: Half Section of a Symmetrical Valve Body Consider a symmetrical valve body used in a water pipeline in the Northern Cape. A half section is ideal for showing both the internal details and the external shape.

Orthographic Projection: Draw the front view of the valve body. Indicate the cutting plane line, which extends halfway through the object.

Sectional View: Draw the front view, showing one half in section and the other half in full view.

Hatching: Hatch the cut areas.

Labeling: Label the sectional view appropriately. 2.2 Simple Assemblies: Putting It All Together An assembly drawing shows how multiple individual components fit together to form a complete product or system. Understanding how to read and create assembly drawings is crucial for manufacturing and maintenance.

Key Features of Assembly Drawings: Bill of Materials (BOM): A table that lists all the parts used in the assembly, along with their part numbers, descriptions, quantities, and materials.

Part Numbers (Ballooning): Each part in the assembly is identified with a number, which is referenced in the BOM. These numbers are usually placed in circles (balloons) and connected to the corresponding part with a leader line.

Assembly Instructions: Sometimes, assembly drawings include notes or instructions on how to assemble the components.

Sectional Views: Assembly drawings often use sectional views to show how the internal parts of the assembly fit together.

Example 3: Simple Assembly of a Bolt and Nut Let's consider the assembly of a simple bolt and nut used in a construction project in Gauteng.

Individual Components: Draw the orthographic projections of the bolt (including thread detail) and the nut.