Lesson Notes By Weeks and Term v5 - Grade 12
Complex assemblies and detailed working drawings – Week 5 focus
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Complex assemblies and detailed working drawings – Week 5 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: 1st Term
Week: 5
Theme: General lesson support
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This week, we delve into the intricate world of complex assemblies and detailed working drawings. This is where all your previous knowledge converges to create comprehensive technical documentation for manufactured products. Understanding assemblies and detailed working drawings is crucial because it forms the bedrock of South Africa's manufacturing, engineering, and construction sectors. From designing and producing agricultural machinery that supports our farmers to creating the infrastructure that connects our cities, the ability to accurately represent complex systems through technical drawings is essential for economic growth and development.
2.1 Assembly Drawings: An assembly drawing shows how different parts of a product fit together. It is not meant to be a detailed manufacturing drawing for individual parts. Instead, it gives a general overview of the complete unit.
Purpose: To show how components fit together, visualize the assembled product, and identify parts by their numbers in the bill of materials.
Characteristics: Simplified representation of individual parts. Part numbers (ballooned) that link to the Bill of Materials. Hidden detail is generally omitted unless necessary for clarity. Section views often used to reveal internal features. Exploded views are used to show the order of assembly.
Example: Imagine an assembly drawing of a gear pump used in agricultural irrigation. The drawing shows the casing, gears, seals, and bolts all fitted together. It wouldn't show the exact surface finish of the gears, but it would show how they mesh and fit within the casing. 2.2 Detailed Working Drawings: A detailed working drawing provides all the information needed to manufacture a single component of an assembly. This includes dimensions, tolerances, materials, surface finishes, and any other specific manufacturing instructions.
Purpose: To provide comprehensive information for manufacturing a part.
Characteristics: Complete dimensioning, including overall dimensions, feature sizes, and location dimensions. Application of tolerances (dimensional and geometric) to ensure proper fit and function. Surface finish specifications (e.g., Ra values). Material specifications (e.g., cast iron, steel grade). Notes specifying manufacturing processes (e.g., "Heat treat to Rockwell C 50"). Multiple views (orthographic projections) to fully define the part geometry.
Example: Imagine a detailed working drawing for one of the gears in the gear pump. This drawing would specify the exact number of teeth, the tooth profile, the bore diameter, the material, the surface hardness, and the permissible tolerances for each of these features. 2.3 Bill of Materials (BOM): The BOM is a comprehensive list of all the parts, components, and materials required to manufacture an assembly. It is a crucial document for purchasing, inventory control, and production planning.
Purpose: To list all components of an assembly and track their quantities and specifications.
Characteristics: Part Number: A unique identifier for each component.
Description: A brief description of the component.
Quantity: The number of units of that component required for one assembly.
Material: The material from which the component is made.
Unit Cost (Optional): The cost of one unit of the component.
Vendor (Optional): The supplier of the component.
Example BOM: | Part Number | Description | Quantity | Material | |---|---|---|---| | GP-001 | Gear Pump Casing | 1 | Cast Iron | | GP-002 | Drive Gear | 1 | Steel, EN8 | | GP-003 | Driven Gear | 1 | Steel, EN8 | | GP-004 | Seal | 2 | Rubber | | GP-005 | Bolt, M8 x 25 | 4 | Steel | 2.4 Section Views: Section views are used to reveal internal features of an object that would be hidden in a regular view. Different types of section views exist, each with its own purpose: Full Section: The cutting plane passes entirely through the object.
Half Section: The cutting plane passes halfway through the object, showing half of the object in section and the other half in a regular view. Often used for symmetrical objects.
Offset Section: The cutting plane is bent or offset to pass through features that are not in a straight line.
Revolved Section: A section view that is rotated 90 degrees and superimposed on the regular view. Used to show the shape of a rib or spoke.
Removed Section: A section view that is drawn separately from the regular view, usually to a larger scale. 2.5 Tolerances: Tolerances define the permissible variation in the size or shape of a component. They are essential for ensuring that parts fit together correctly and function as intended.
Dimensional Tolerances: Specify the allowable variation in a linear dimension (e.g., ±0.1 mm).
Geometric Tolerances: Specify the allowable variation in the form, profile, orientation, or location of a feature (e.g., flatness, perpendicularity, position).