Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Construct isometric drawings from orthographic projections (and vice versa).
• Select and arrange appropriate views according to SANS 10111 standards.
• Apply correct conventions for hidden detail, center lines, and cutting planes.
• Solve problems using these projection principles.

Lesson summary

This week marks the start of our focused revision for the end-of-year Grade 11 Engineering Graphics and Design (EGD) examinations. Mastering EGD is crucial, not just for passing the exam, but also for opening doors to various career paths in South Africa. From civil engineering (designing infrastructure like roads and bridges) to mechanical engineering (designing machines and tools), and even architecture (designing buildings), a solid foundation in EGD is essential.

Furthermore, with the increasing emphasis on technical skills and infrastructure development in South Africa, proficient EGD skills are highly sought after by employers.

Lesson notes

This week will focus on Isometric and Orthographic Projections. These are two fundamental drawing techniques used to represent three-dimensional objects in two dimensions.

A. Orthographic Projection: Definition: Orthographic projection is a method of representing a 3D object using multiple 2D views, each showing the object from a different direction. The views are typically the Front View (elevation), Top View (plan), and Right View (side elevation). These views are projected onto planes that are perpendicular to each other.

Principle: The object is viewed from an infinite distance, so all projection lines are parallel and perpendicular to the projection plane. This ensures that the object's shape and dimensions are accurately represented in each view.

Standard Arrangement (SANS 10111): In South Africa, we follow the First Angle Projection method, and less frequently, the Third Angle Projection method. The exam normally specifies the angle of projection to use.

First Angle Projection means: The Front View is above the Top View. The Right View is to the left of the Front View.

Hidden Detail: Hidden lines are represented by dashed lines. They show edges and surfaces that are not visible from the current viewpoint.

Center Lines: Center lines are used to indicate the center of circles, arcs, and symmetrical features. They are represented by long-dashed dotted lines.

Cutting Planes: Cutting plane lines are used to indicate the location of an imaginary cut through an object. They are represented by thick chain lines with arrowheads indicating the direction of view. The cut surface is then shown with hatching.