Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Define sectional views and their purpose.
• Draw full sectional views of simple objects.
• Apply correct hatching conventions for cut surfaces.
• Interpret simple assembly drawings.
• Create a simple assembly drawing.

Lesson summary

Sectional views are a crucial tool in engineering drawings because they allow us to see the internal details of an object. Imagine trying to understand how a lock works, or the internal mechanism of a water tap, without being able to see inside it. Sectional views are like taking a "slice" through the object to reveal its hidden features. This skill is particularly relevant in South Africa, where manufacturing, construction, and infrastructure development are key sectors. Understanding how components fit together (assembly) is also critical, allowing us to create complex products from simple parts.

Lesson notes

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Sectional Views: Unveiling the Interior A sectional view is a drawing technique used to reveal the internal features of an object that would otherwise be hidden from view in a regular orthographic projection. It's created by imagining that the object has been cut through by a cutting plane. The part of the object in front of the cutting plane is then removed, revealing the internal details.

Types of Sectional Views: Full Section: The cutting plane passes entirely through the object, dividing it into two halves. One half is removed, and the remaining half is drawn in section. This is the most common type of sectional view.

Half Section: The cutting plane extends only halfway through the object. This is typically used for symmetrical objects. One quarter of the object is removed, revealing both the external and internal features in a single view.

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

Broken-Out Section: A small portion of the object is broken away to reveal an internal feature, while the rest of the object remains in its original form. 2.

2. Cutting Plane Line: The cutting plane line indicates the location of the imaginary cut. It is a thick, dashed line with arrows at both ends pointing towards the viewing direction. The arrows are usually labeled with letters (e.g., A-A, B-B) to identify the corresponding sectional view. 2.

3. Hatching (Section Lines): Hatching, also known as section lines, is used to indicate the areas that have been "cut" by the cutting plane. Different hatching patterns represent different materials.

General Purpose Hatching: The most common type of hatching consists of evenly spaced, thin lines drawn at a 45-degree angle to the horizontal. This is used for many common materials like steel and cast iron.

Specific Material Hatching: Certain materials have specific hatching patterns assigned to them in standards like SANS

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1. However, for simplicity in Grade 10, we will primarily focus on general purpose hatching. The most important thing is to maintain consistency within a single drawing.

Important Hatching Rules: All areas that are "cut" by the cutting plane in a single component must be hatched identically. Different components in an assembly should have different hatching angles or spacing to distinguish them. A 30-degree or 60-degree angle can be used, or the spacing between lines can be altered. Hatching lines should be thin and evenly spaced. Hatching should not run parallel or perpendicular to the visible outline of the sectioned area. Hidden detail lines are not shown in the sectional view within the hatched area.

However, hidden details behind the cutting plane can still be shown. 2.

4. Simple Assemblies: An assembly drawing shows how multiple individual components fit together to form a complete product or system.

Assembly drawings typically include: Item Numbers (Balloon Numbers): Numbers that identify each component in the assembly. These numbers are usually placed in circles connected to the component with a leader line.

Bill of Materials (BOM): A table that lists all the components used in the assembly, along with their item numbers, descriptions, quantities, and material specifications.

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

Example 1: Full Section of a Simple Bracket Imagine a simple L-shaped bracket made of steel. Let's say it has a hole drilled through one of its legs. If we draw a standard orthographic view, we won't be able to see the hole clearly.

Draw the Front View: Draw the front view of the bracket. Include hidden detail lines for the hole.

Draw the Cutting Plane Line: Draw a cutting plane line vertically through the center of the front view, passing through the hole. Label the cutting plane line A-A with arrows pointing to the right.

Draw the Sectional View (Right View): Imagine cutting the bracket along the cutting plane and removing the left half. Draw the right view, showing the cut surface.

Hatch the Cut Surface: Hatch the cut surface with general-purpose hatching (45-degree angle). The hole will now be visible as a clear, un-hatched circle.

Remove Hidden Detail Lines: Remove the hidden detail lines within the hatched area in the right view.

Example 2: Simple Assembly – Bolt and Nut Consider a bolt passing through a plate, secured by a nut and washer.

Draw the Individual Components: Draw the bolt, nut, washer, and plate separately, showing their dimensions and features. Use standard conventions for representing threads on the bolt.

Position the Components: Decide how the components will be assembled. In this case, the bolt passes through the plate, the washer is placed on the bolt, and the nut is tightened to secure the assembly.