Lesson Notes By Weeks and Term v5 - Grade 12
Revision and examination preparation (Grade 12 EGD) – Week 2 focus
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Revision and examination preparation (Grade 12 EGD) – Week 2 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Engineering Graphics and Design
Class: Grade 12
Term: Term 4
Week: 2
Theme: General lesson support
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This week focuses on strategic revision and exam preparation techniques in Engineering Graphics and Design (EGD). EGD equips you with crucial skills applicable far beyond the classroom. From understanding architectural blueprints for new housing developments in your community to visualizing and designing solutions for everyday engineering challenges, EGD knowledge is highly valuable. South Africa's growing infrastructure necessitates skilled individuals who can interpret and create technical drawings, contributing directly to national development. Mastering EGD means participating in this progress.
This week's focus will be on consolidating and applying existing knowledge rather than introducing new concepts.
However, we will revisit key areas that frequently appear in examinations and often pose challenges for students. These areas are Isometric and Orthographic Projections, Sectional Views, Developments, CAD applications, and specific South African context applications. 2.1 Isometric and Orthographic Projections: The Foundation of EGD Understanding the relationship between Isometric and Orthographic projections is fundamental. Orthographic projection represents an object using multiple two-dimensional views (front, top, side) to convey its exact shape and dimensions. Isometric projection, on the other hand, provides a three-dimensional pictorial representation of the object.
Orthographic Projection: Remember the principles of first-angle or third-angle projection (South Africa uses first-angle). Each view shows only two dimensions. Hidden detail is shown with dashed lines. Dimensioning is crucial for clarity and accuracy.
Isometric Projection: All three axes are equally inclined at 120 degrees to each other. Lines parallel to the isometric axes are measured using true lengths. Non-isometric lines need to be located using coordinates. Using the Box method when drawing isometric shapes is very helpful.
Example 1: Draw the orthographic views (front, top, and left) and the isometric view of a rectangular prism 60mm long, 40mm wide, and 30mm high.
Orthographic: Front view: A rectangle 60mm x 30mm.
Top view: A rectangle 60mm x 40mm.
Left view: A rectangle 40mm x 30mm. Each view is precisely aligned with the others, adhering to first-angle projection principles. Dimensions are clearly indicated on all views.
Isometric: Start by drawing the isometric axes. Measure 60mm along the horizontal axis, 40mm along the axis angled to the right, and 30mm along the vertical axis. Complete the isometric prism by drawing lines parallel to the axes. Ensure all edges are visible and properly aligned. 2.2 Sectional Views: Revealing Internal Details Sectional views are used to expose internal features of an object that would otherwise be hidden. A cutting plane line indicates where the object is "cut". The cut surface is then hatched (usually at 45 degrees).
Full Section: The cutting plane passes entirely through the object.
Half Section: The cutting plane cuts halfway through the object. One half of the view is in section, and the other half is not.
Offset Section: The cutting plane is bent to pass through specific features.
Example 2: A cylindrical block has a hole drilled through its center. Draw the front view in full section. Draw the front view of the cylinder. Draw a cutting plane line vertically through the center of the cylinder. Add sectioning lines to the surfaces that have been "cut". Hidden detail inside the cylindrical bore is now visible after the sectioning. 2.3 Developments: Creating Flat Patterns Developments are the flat patterns that can be folded to form a three-dimensional object. This is crucial for manufacturing sheet metal products.
Prisms: The development consists of rectangles representing the sides, plus top and bottom faces.
Cylinders: The development is a rectangle (length = circumference, width = height), plus two circles.
Pyramids: The development consists of triangles radiating from a central point, plus a base.
Cones: The development is a sector of a circle.
Example 3: Develop a square prism with sides of 30mm and a height of 50mm. Draw a rectangle 4 x 30mm = 120mm long and 50mm high. This is the main body of the prism. Attach a 30mm x 30mm square to the top and bottom edges of the rectangle. These are the top and bottom faces. Add tabs for gluing/joining the edges. 2.4 CAD Applications: Mastering Digital Drafting CAD software is an indispensable tool for modern EGD. Familiarize yourself with commands for drawing lines, circles, arcs, and other basic shapes. Also, practice using commands for modifying objects, such as trimming, extending, copying, and mirroring. Being able to apply CAD under exam conditions requires speed and accuracy.
Example 4: Using CAD, draw the isometric view of a house. Start by creating a new drawing in your CAD software. Set the isometric snap and grid settings. Use the line command to draw the base of the house. Use the copy and offset commands to create the walls. Add the roof using the line command. Add windows and doors using the rectangle and line commands. Apply appropriate dimensions and annotations. 2.5 South African Context Applications: EGD's Relevance Consider how EGD is used in South Africa. Think about designing a low-cost housing structure using locally available materials, or improving the water distribution system in a rural community. Focus on sustainable and practical solutions.
Example 5: Design a sustainable rainwater harvesting system for a rural school in South Africa.