Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Apply orthographic projection principles.
• Use CAD or manual drafting to SANS standards.
• Solve complex geometric construction problems.
• Interpret assembled and exploded views.
• Analyse Civil Technology drawings (plans, elevations, sections).

Lesson summary

This week focuses on consolidating your understanding of the Grade 11 EGD curriculum in preparation for upcoming assessments, including the end-of-year examination. Engineering Graphics and Design skills are vital in various South African industries, from construction and manufacturing to architecture and engineering. Proficiency in EGD allows you to visualize, interpret, and communicate technical information effectively, contributing to the development of infrastructure and innovative solutions within our country.

Lesson notes

This section will comprehensively revise the core concepts required for success in Grade 11 EGD. 2.1 Orthographic Projection: Orthographic projection is a method of representing a three-dimensional object in two dimensions. It involves projecting the object onto multiple planes, typically the front, top, and side planes. Understanding first-angle and third-angle projection is critical. In first-angle projection, the object is placed behind the projection plane, and the view is projected onto the plane. This means the front view is above the top view, and the side view is to the left of the front view. This is not common in South Africa. In third-angle projection, the object is placed in front of the projection plane, and the view is projected through the object onto the plane. This means the front view is below the top view, and the side view is to the right of the front view. This is the standard convention used in South Africa and internationally.

Example: Imagine a simple rectangular block. In third-angle projection, if you are looking at the front of the block, the top view would be drawn above the front view, showing the block's width and depth. The right-side view would be drawn to the right of the front view, showing the block's height and depth. 2.2 CAD (Computer-Aided Design) and SANS Standards: CAD software simplifies the drafting process and ensures accuracy.

However, understanding SANS standards is equally important. SANS standards define conventions for line types (e.g., continuous lines for visible edges, dashed lines for hidden edges, center lines), dimensioning (placement, arrowheads, extension lines), annotation (text size, font), and sectioning (hatching patterns).

Example: When dimensioning a drawing of a chair leg, the dimension lines should be placed outside the object, with extension lines extending from the leg to the dimension lines. The dimension value should be placed above the dimension line. SANS specifies the standard size of arrowheads and the spacing between the object and the dimension line. Section lines should also conform to standards depending on the material of the sectioned component. 2.3 Geometric Constructions: Geometric constructions involve creating precise geometric shapes using only a compass and straightedge (or CAD equivalents). Common constructions include bisecting lines and angles, drawing perpendicular and parallel lines, dividing a line into equal parts, constructing polygons, and drawing tangents to circles and arcs.

Example: To draw a tangent to a circle from a point outside the circle: Connect the point to the center of the circle. Bisect the line segment connecting the point and the center. Draw a circle with the midpoint of the line segment as its center and the radius equal to half the length of the line segment. The points where this new circle intersects the original circle are the points of tangency. Draw lines from the external point to the points of tangency; these are the tangents. The ability to construct loci (the path of a moving point) is also essential. This is particularly useful when designing linkages or mechanisms. 2.4 Assembled and Exploded Views: Assembled views show how different parts of a machine or mechanism fit together. Exploded views show the same parts separated and arranged in a way that illustrates their relative positions and assembly sequence. Exploded views are often accompanied by parts lists that identify each component.

Example: Consider a simple bolt and nut assembly. The assembled view shows the bolt passing through a hole in a plate and the nut tightened on the other side. The exploded view would show the bolt, nut, and plate separated, with arrows indicating how they are assembled. 2.5 Civil Technology Drawings Civil technology drawings are used in the construction industry. They show different aspects of a building and its surroundings.

The drawings included are: Site plans, floor plans, elevations and sections of a building.

Site Plans: Shows the buildings in relation to the boundary lines and other site features.

Floor Plans: Shows the layout of a building as seen from above by removing the roof.

Elevations: Shows the exterior view of a building, one side at a time.

Sections: Shows a cut-through view of a building to reveal interior details.

Example: Imagine a set of house plans. The site plan shows the house positioned on the erf, including the driveway, garden and swimming pool. The floor plan shows the layout of rooms, including bedrooms, bathrooms and living area. The elevations show the front, back and side views of the house. The sections show the interior details of the house, including the roof structure, wall construction and flooring. Guided Practice (With Solutions)

Question 1: Draw, using third-angle orthographic projection, the front view, top view, and right-side view of a rectangular prism with dimensions 80mm x 50mm x 30mm (length x width x height).