Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Identify and explain the purpose of different types of views.
• Apply conventions for representing standard components like fasteners and bearings.
• Create detailed working drawings of individual components.
• Interpret and analyze complex assembly drawings.

Lesson summary

This week, we delve into the world of complex assemblies and detailed working drawings. This is a crucial area of Engineering Graphics and Design (EGD) because it forms the backbone of manufacturing and construction industries. Imagine the Gautrain project or the construction of a new hospital - these complex projects rely heavily on accurate and comprehensive working drawings to ensure that all the components fit together correctly and the final product functions as intended. In South Africa, with our growing infrastructure needs and focus on local manufacturing, the ability to interpret and create complex assembly drawings is a highly valuable skill.

Lesson notes

2.1 Assembly Drawings: The Big Picture An assembly drawing depicts how different parts or components fit together to form a complete product or machine. It shows the spatial relationships between the parts and indicates how they are assembled. Think of it as a roadmap for putting something together.

Purpose: To show the complete product, its components, and their relative positions. It's used for assembly instructions, identifying parts, and understanding the overall functionality.

Characteristics: Includes a parts list or bill of materials (BOM) that identifies each component with a unique number or name. This BOM should include material specifications, quantity, and other relevant information. Shows all the parts in their assembled positions. May include balloons or leader lines that point from the part in the drawing to its corresponding entry in the parts list. Typically includes dimensions that define the overall size and important locations of the assembly. May utilize different types of views (e.g., orthographic, isometric, sectional) to provide a complete understanding of the assembly. 2.2 Types of Views in Assembly Drawings Orthographic Views: These are the standard front, top, and side views that show the assembly from different perspectives. They are essential for understanding the overall shape and size of the assembly.

Sectional Views: These views are created by imagining the assembly is cut through by a plane. They reveal the internal details of the assembly that would otherwise be hidden. There are different types of sectional views (e.g., full section, half section, offset section) depending on the features being highlighted. A Full Section shows the assembly cut completely through. A Half Section shows one half of the assembly in section and the other half in elevation.

Exploded Views: These views show the parts of the assembly separated from each other but in their relative positions. They are extremely helpful for understanding how the parts fit together and the sequence of assembly. They're excellent for manuals and instructions.

Auxiliary Views: Used when features are on inclined planes, auxiliary views provide a true shape and size representation of these features. 2.3 Standard Components: Fasteners and Bearings In assembly drawings, standard components like fasteners (bolts, nuts, screws, rivets) and bearings are often represented using simplified conventions to save time and effort.

Fasteners: Bolts, Nuts, and Screws: Instead of drawing every thread, these are often represented by simplified symbols. A simple "T" shape can represent a bolt head or nut, and a straight line can represent the shank. The type of thread (metric, unified) and size should be indicated in the BO

M. Rivets: Similar to bolts, rivets are often represented by simplified symbols.

Bearings: Rolling-element bearings (ball bearings, roller bearings) are critical components in many assemblies. These are often represented schematically using circles and arcs to indicate the races and rolling elements. Again, the specific bearing type and size should be noted in the BOM. 2.4 Detailed Working Drawings: Individual Component Documentation Detailed working drawings provide all the information needed to manufacture a single component of the assembly.

They include: Multiple Views: Typically orthographic views (front, top, side) to fully describe the component's shape.

Dimensions: Accurate and complete dimensions that specify the size, shape, and location of all features.

Tolerances: Allowable variations in dimensions to ensure proper fit and function.

Surface Finish: Specifies the required smoothness or roughness of the component's surfaces.

Material: Specifies the type of material the component is made from (e.g., steel, aluminum, plastic).

Manufacturing Processes: May include notes about specific manufacturing processes required (e.g., machining, casting, welding).

Example 1: Representing a Bolt and Nut Instead of drawing the complex helical threads of a bolt and nut, we can use a simplified representation. The bolt head is shown as a hexagon, and the nut is similarly represented. A center line runs along the length of the bolt. This saves a lot of drawing time without sacrificing clarity in the assembly drawing.

Example 2: Sectional View of a Gearbox Imagine a gearbox assembly. Drawing all the internal gears and shafts in solid lines would create a very cluttered and confusing drawing. Instead, we use a sectional view. We imagine cutting the gearbox in half, revealing the internal components. Hatching (parallel lines) is used to indicate the cut surfaces. This allows us to clearly see the arrangement of gears, bearings, and shafts within the gearbox.

Example 3: Detailed Drawing of a Shaft Consider a shaft that needs to be manufactured for a mechanical device. The detailed drawing will show a front view, and perhaps a sectioned side view to illustrate the interior.