Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Interpret and analyze integrated civil and mechanical EGD problems.
• Apply principles of orthographic projection, sectioning, and dimensioning.
• Apply relevant SANS standards and conventions.
• Solve problems involving the intersection of solids.
• Communicate design ideas effectively through correct EGD drawings.

Lesson summary

This week, we're tackling integrated Engineering Graphics and Design (EGD) tasks that combine civil and mechanical drawing principles. These types of questions are common in the final Grade 12 EGD exam and require you to apply knowledge from both disciplines to solve a single, often complex, problem. Successfully navigating these integrated tasks demonstrates a comprehensive understanding of EGD principles and their practical applications.

Lesson notes

Integrated EGD tasks require you to synthesize your knowledge of both civil and mechanical engineering drawing principles. Here's a breakdown of key concepts and how they apply in integrated scenarios: 2.1 Orthographic Projection: This is the foundation of all EGD drawings. You must accurately project views from one plane to another (Front View, Top View, Side View) to fully represent the 3D object. In integrated tasks, you'll likely need to project civil elements (like building foundations) and mechanical elements (like pumps or engines) together.

Example: Imagine a task where you need to draw the foundation for a small pumping station. The pump itself is a mechanical component, while the foundation is a civil structure. You'll need to accurately project the pump's mounting points (mechanical) onto the foundation (civil) to ensure proper alignment. 2.2 Sectioning: Sectioning is used to reveal internal details.

Different types of sections exist: Full Section, Half Section, Offset Section, and Removed Section. The choice of section depends on the complexity and symmetry of the object. Remember to use correct hatching conventions for different materials (steel, concrete, etc.).

Example: A task might ask you to draw a section view through a water pipe connecting to a storage tank. You'd need to show the internal diameter of the pipe, the wall thickness, the flange connecting it to the tank, and the reinforcement within the concrete tank wall, all correctly hatched. 2.3 Dimensioning: Accurate dimensioning is crucial for manufacturing and construction. Follow SANS standards for dimensioning (extension lines, dimension lines, arrowheads, and text). Dimensions should be clear, concise, and avoid redundancy. Use aligned or unidirectional dimensioning, as appropriate.

Example: If you are drawing the details of a concrete beam supporting a piece of machinery, you need to dimension the beam's width, height, depth, the location and size of the reinforcing steel, and the distances between supports. All dimensions must be clearly and accurately indicated according to SANS standards. 2.4 Intersection of Solids: Determining the line of intersection between two solids is a common challenge. Use projection methods to find points on the intersection line, then connect these points with a smooth curve (or straight line, depending on the shapes). Remember to consider visibility – hidden lines may be necessary to accurately represent the intersection.

Example: A task might involve a cylindrical pipe intersecting with a rectangular concrete duct. You'll need to accurately determine the curve of intersection where the pipe passes through the duct wall. 2.5 Development of Surfaces: In some cases, you might need to develop the surface of a component. This involves unfolding the 3D shape onto a 2D plane. Common developments include cylinders, prisms, and pyramids. Understanding development is vital for creating templates for fabrication.

Example: Consider a task where you must develop the metal casing for a filter used in a water treatment plant. You would need to accurately develop the surface of the casing to create a template that can be used to cut and bend the metal sheet. 2.6 SANS Standards: Adhering to the South African National Standards (SANS) is mandatory. This includes standards for line types, dimensioning, hatching, symbols, and lettering. Familiarize yourself with the relevant SANS standards for civil and mechanical drawings. SANS 10111 provides general guidelines. 2.7 Civil Specifics: Remember key civil details: Concrete and steel reinforcement (rebar) Earthworks (cut and fill) Foundations (strip footings, raft foundations, pile foundations) Road sections (layers of material, camber) 2.8 Mechanical Specifics: Fasteners (bolts, nuts, screws, rivets) and their standard representations Bearings (ball bearings, roller bearings) and their housings Shafts and couplings Welds and their symbols