Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Engineering Working Drawings
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Engineering Working Drawings
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Subject: Technical Drawings
Class: Senior Secondary 3
Term: 3rd Term
Week: 1
Theme: Building And Engineering Drawing
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Prepare the working drawings of simple machines parts Prepare working drawings of machine as semblies.
Building And Engineering Drawing screw, positioned 10 mm from one end.
Task: Prepare a complete detail working drawing of this Shaft Collar. Ensure all necessary orthographic views are included, fully dimensioned, with material specification, and surface finish indications where appropriate.
Marking Scheme for Question 1: Orthographic Views (20 marks): Correct number and type of views (Front, Top, Sectional Side/End views) - 10 marks Accuracy of feature representation (bore, tapped hole, centre lines) - 10 marks Dimensioning (20 marks): Completeness (all necessary dimensions) - 10 marks Correctness and clarity (placement, extension lines, dimension lines, values) - 10 marks Drawing Conventions (15 marks): Correct use of line types (visible, hidden, centre lines) - 5 marks Symbols (diameter, chamfer, surface finish) - 5 marks Projection method (First Angle) - 5 marks Information (10 marks): Material specification (Aluminium) - 5 marks Title Block completeness and accuracy - 5 marks Overall Presentation (5 marks): Neatness, legibility, and adherence to sheet layout. Question 2 (Machine Assembly Working Drawing): A small hand press used for cassava processing in rural communities needs an assembly drawing for its 'Ram Assembly'.
The assembly consists of:
1. Ram Body: Steel, Ø50 mm, 200 mm long, with a Ø20 mm threaded hole (M20x2.5) at one end, 30 mm deep.
2. Pressing Foot: Steel, Ø60 mm, 20 mm thick, with a central M20x2.5 threaded hole.
3. Guide Bush: Bronze, Ø50H7 outer, Ø40 inner, 50 mm long (fits into a guide housing, not drawn).
Note: Assume the Guide Bush slides over the Ram Body, and the Pressing Foot screws into the Ram Body.
Task: Prepare an assembly drawing showing the Ram Body, Pressing Foot, and Guide Bush assembled. Include a sectional front view, item numbers, and a complete Bill of Material.
Marking Scheme for Question 2: Orthographic Views (20 marks): Correct choice and representation of sectional view - 10 marks Accuracy of assembly fit and relationship between parts - 10 marks Assembly Information (25 marks): Item Numbers (Balloons) correctly placed and legible - 10 marks Bill of Material completeness and accuracy (Item No., Description, Material, Quantity) - 15 marks Drawing Conventions (10 marks): Correct use of line types and hatching for different materials - 5 marks Projection method (First Angle) - 5 marks Overall Presentation (5 marks): Neatness, legibility, and adherence to sheet layout.
7. Real-life Applications / Integration
1. Local Manufacturing and Fabrication: Engineering working drawings are indispensable in local fabrication workshops (e.g., in places like Nnewi, Onitsha, or Kano) for manufacturing gates, furniture, agricultural tools (e.g., ploughs, planters), vehicle spare parts, and custom machinery. Students skilled in preparing these drawings can be employed to design and document products for these enterprises, improving product quality and reducing manufacturing errors.
2. Infrastructure Development and Maintenance: In road construction, bridge building, and public works projects across Nigeria, working drawings are used for structural steel components, specialized equipment, and custom fittings. For example, designing custom brackets for streetlights or specific components for water treatment plants requires precise working drawings. The maintenance of existing infrastructure also relies heavily on accurate "as-built" drawings.
3. Oil and Gas Industry: The Nigerian oil and gas sector heavily utilizes engineering working drawings for designing, fabricating, installing, and maintaining pipelines, pumps, valves, storage tanks, and offshore platforms. Precision is critical for safety and operational efficiency. Students understanding these drawings can pursue technical roles in this vital sector.
4. Entrepreneurship: With these skills, students can become independent technical illustrators or designers, offering services to small and medium enterprises (SMEs) that lack in-house technical drawing capabilities. They could design modifications for existing machinery, create designs for new locally manufactured products (e.g., food processing equipment, energy solutions), and assist in documentation, fostering local innovation and job creation.
8. Differentiation, Remediation and Extension
A. Remediation (for struggling learners):
1. Simplified Exercises: Provide simpler components for detail drawing (e.g., a plain block, a simple washer) focusing only on orthographic views and basic linear dimensioning.
2. Step-by-Step Templates: Offer partially completed drawings or templates where students only need to add dimensions, specific and medium enterprises (SMEs) that lack in-house technical drawing capabilities. They could design modifications for existing machinery, create designs for new locally manufactured products (e.g., food processing equipment, energy solutions), and assist in documentation, fostering local innovation and job creation.
8. Differentiation, Remediation and Extension
A. Remediation (for struggling learners):
1. Simplified Exercises: Provide simpler components for detail drawing (e.g., a plain block, a simple washer) focusing only on orthographic views and basic linear dimensioning.
2. Step-by-Step Templates: Offer partially completed drawings or templates where students only need to add dimensions, specific features (like holes), or complete the title block.
3. Visual Aids and Tracing: Use clear, large visual aids (pre-drawn charts, projected images) to show correct line types, dimensioning styles, and symbol usage. Allow students to trace over correct examples to develop muscle memory and accuracy.
4. One-on-One Support: Provide individualized attention, breaking down complex instructions into smaller, manageable steps. Focus on mastering one concept (e.g., centre lines) before moving to another.
5. Peer Tutoring: Pair struggling learners with more proficient students for mutual learning and support.
B. Extension (for high-achieving learners):
1. Advanced Component Design: Challenge students to prepare working drawings for more complex machine parts, such as a crankshaft, a cam profile, or a gear wheel, requiring more intricate dimensioning and sectional views.
2. Complex Assembly Design: Task students with creating an assembly drawing of a multi-component machine system, like a gear train, a small engine part, or a complete vice mechanism. This would involve managing many parts and a detailed Bill of Material.
3. Research and Application of Standards: Encourage research into specific Nigerian Industrial Standards (NIS) related to technical drawings or specific industries (e.g., welding symbols, pipe fitting standards). Students could present their findings.
4. Introduction to CAD: Introduce them to free or trial versions of Computer-Aided Design (CAD) software (e.g., TinkerCAD, FreeCAD, or basic AutoCAD tutorials online). This will expose them to modern industrial practices and enable them to transfer their manual drawing skills to digital platforms, which is highly relevant in current engineering fields.
Engineering Working Drawings Term: 3rd Term Week: 4 ---
1. Overview and Learning Objectives This topic, Engineering Working Drawings, is crucial for students pursuing careers in engineering, manufacturing, and technical fields in Nigeria. It bridges the gap between design concepts and the actual fabrication or construction of products. Understanding working drawings is fundamental for communicating precise technical information, ensuring that components are manufactured correctly and assemblies fit together as intended. This skill is highly valued in various Nigerian industries, including fabrication, automotive repair, oil and gas, agriculture, and construction, where accurate technical communication is paramount for efficiency and safety. Upon completion of this lesson, students will be able to: Create detailed technical drawings for individual machine components, showing all necessary information for their manufacture. Produce technical drawings that illustrate how multiple machine components fit together to form a complete assembly. Apply standard conventions for dimensioning, tolerancing, and material specification in their drawings. Interpret engineering working drawings used in various industries within Nigeria.
2. Key Concepts and Explanations Engineering working drawings are a complete set of graphical instructions used to manufacture or assemble a product. They serve as the primary communication tool between designers and manufacturers, ensuring that a product is built exactly to specifications.
A. Types of Working Drawings:
1. Detail Drawings: These drawings provide a complete and unambiguous description of a single machine part. They contain all the information required to manufacture that specific part.
Orthographic Views: Typically include front, top, and side views (using First Angle Projection, which is standard in Nigeria and Europe) to show the true shape and features of the part. Sectional views are used to reveal internal features.
Dimensioning: All critical dimensions required for manufacturing the part (lengths, widths, heights, diameters, radii, hole locations) must be clearly indicated using standard dimensioning practices.
Tolerances: Permissible variations in dimensions and geometric forms (e.g., flatness, perpendicularity).
Dimensional Tolerances: Specify the upper and lower limits of a dimension (e.g., 25 ± 0.1 mm). This is critical for ensuring interchangeability and proper fit.
Geometric Tolerances: Specify the allowable deviation from perfect form, orientation, and location (e.g., flatness, parallelism, concentricity).
Surface Finish Symbols: Indicate the desired smoothness or roughness of machined surfaces (e.g., grinding, turning, milling).
Material Specification: Clearly state the type of material the part is to be made from (e.g., Mild Steel, Aluminium Alloy 6061, Cast Iron SG400).
Heat Treatment: If applicable, specifications for heat treatment processes (e.g., hardening, tempering, annealing) are included.
Part Number and Quantity: Unique identifier for the part and the number required.
Title Block: Contains essential information such as drawing title, drawing number, scale, designer, checker, date, material, and company name (e.g., "XYZ Engineering Ltd., Kaduna").
2. Assembly Drawings: These drawings show how individual components (parts) fit together to form a complete machine or sub-assembly. They primarily focus on the relationship and functionality of parts.
Orthographic Views: May include front, top, and side views of the assembled product. Sectional views are often used to show internal relationships between components.
Exploded Views: Show how parts are separated along an axis but aligned to indicate their assembly sequence. This is very useful for assembly instructions and maintenance.
Item Numbers (Balloons): Circles with numbers or letters pointing to each component in the assembly, linking them to the Bill of Material (BOM).
Bill of Material (BOM) / Parts List: A table listing all components in the assembly, including item number, part number, description, material, quantity, and sometimes vendor information. This is usually placed within or adjacent to the title block.
Overall Dimensions: May show important overall dimensions for installation or space requirements. Individual component dimensions are usually omitted as they are detailed in individual part drawings.
Notes: General instructions for assembly, lubrication, fastening torque, or testing procedures.
B. Drawing Standards and Conventions (Relevant to Nigerian Context): Line Types: Different line types convey specific meanings (e.g., continuous thick for visible outlines, dashed for hidden lines, thin chain for centre lines).
Dimensioning Principles: Dimensions should be placed clearly, avoid redundancy, and be readable from the bottom or right side of