Engineering Working Drawings of Brackets, Sleeves and Cylinders for SS 3

Class: SS 3
Term: First Term
Week: 5
Age: 17 years
Duration: 60 minutes
Subject: Technical Drawing
Curriculum Theme: Engineering Working Drawings
Previous Lesson: Locking Devices and Their Applications
Topic: ENGINEERING WORKING DRAWINGS.
Subject Matter: Example of machine parts; g. brackets, sleeves cylinders etc

Specific Objectives

By the end of the lesson, pupils/students should be able to:

Cognitive Domain

• Identify common machine parts requiring working drawings, such as brackets, sleeves, and cylinders.
• Describe the purpose and importance of engineering working drawings.
• State the essential elements found in a complete working drawing.

Affective Domain

• Appreciate the importance of accuracy and precision in technical drawing.
• Show interest in creating detailed engineering drawings for machine parts.

Psychomotor Domain

• Prepare orthographic views of simple machine parts like brackets, sleeves, and cylinders.
• Apply correct dimensioning techniques to working drawings.
• Construct a complete working drawing of a given simple machine part.

Reference Materials

The following resources were used in planning this lesson:

• 2014 Senior Secondary Education Curriculum (SSEC)
• Relevant State Unified Scheme of Work
• Technical Drawing for Senior Secondary Schools by A.B. Oluyemi
• FCT ERC/NAPPS Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Drawing board, T-square, set squares, protractor, compass, pencils (HB, H, 2H), eraser.
• Drawing paper.
• Examples of actual machine parts (e.g., crank, pedal, simple bracket, sleeve, cylinder) or their models.
• Sample engineering working drawings of simple machine parts.
• Whiteboard and markers.

Rationale for the Lesson

This lesson is important as it equips students with the fundamental skills required to produce clear and precise technical drawings of machine components. Understanding engineering working drawings is crucial for effective communication in engineering and manufacturing, enabling accurate fabrication and assembly of parts. It provides practical experience in applying theoretical knowledge of orthographic projection and dimensioning to real-world objects.

Prerequisite/Previous Knowledge

Pupils/students should have prior knowledge of basic technical drawing principles, including orthographic projection, different types of lines, and basic dimensioning techniques.

Lesson Content/Board Summary

Engineering Working Drawings

What are Engineering Working Drawings?

Engineering working drawings are detailed graphical representations of machine parts or assemblies that provide all the necessary information for their manufacture, assembly, and inspection. They serve as a universal language for engineers, designers, and manufacturers.

Key Features of Engineering Working Drawings

A complete engineering working drawing typically includes:

1. Orthographic Views: Multiple views (e.g., front, top, side) to show the object from different angles, revealing its true shape and features.
2. Sectional Views: Views that show the internal features of an object by cutting through it.
3. Auxiliary Views: Views used to show the true shape of inclined surfaces.
4. Dimensions: Numerical values indicating the size and location of features, including length, width, height, diameters, radii, and angles.
5. Tolerances: Permissible variations in dimensions, indicating the acceptable range for manufacturing.
6. Material Specifications: Information about the material from which the part is to be made.
7. Surface Finish Symbols: Indications of the required smoothness or roughness of surfaces.
8. Title Block: Contains essential information such as the part name, drawing number, scale, date, designer, and company name.
9. Part List/Bill of Materials (for assemblies): A list of all components in an assembly.

Examples of Machine Parts for Working Drawings

Brackets

Brackets are common machine parts used to support or hold other components. They often have complex shapes involving flat surfaces, curves, holes, and ribs. Drawing a bracket requires careful consideration of its functional features and how they are represented in orthographic views.

Example: An L-shaped bracket used to mount a motor.

Sleeves

Sleeves are cylindrical components, often hollow, used to enclose, protect, or connect shafts and other rotating parts. They can be plain, flanged, or stepped. Working drawings of sleeves emphasize their internal and external diameters, lengths, and any specific features like keyways or threads.

Example: A plain bearing sleeve or a coupling sleeve.

Cylinders

Cylinders are fundamental geometric shapes in engineering, appearing as shafts, pins, pistons, or housing components. Their working drawings primarily involve representing their circular ends and cylindrical body in orthographic views, with accurate dimensioning of diameter and length.

Example: A hydraulic cylinder body or a simple cylindrical pin.

General Steps for Preparing Working Drawings of Machine Parts

The process of creating a working drawing involves several key steps:

1. Understand the Part: Carefully study the object or design to understand its function, shape, and critical features.
2. Select Views: Determine the minimum number of orthographic views (e.g., front, top, right side) required to fully describe the object without ambiguity. Consider using sectional or auxiliary views if necessary.
3. Layout the Views: Sketch the chosen views on the drawing paper, ensuring proper spacing for dimensions and notes.
4. Draw Visible Lines: Use continuous thick lines to represent visible edges and contours.
5. Draw Hidden Lines: Use dashed lines to represent hidden edges and features.
6. Draw Centre Lines: Use chain lines to indicate axes of symmetry, centres of circles, and cylindrical features.
7. Add Dimensions: Apply dimensions accurately using appropriate dimensioning techniques (e.g., chain, parallel, or combined dimensioning). Ensure all necessary dimensions for manufacturing are included, avoiding redundancy.
8. Add Notes and Specifications: Include any required notes on material, surface finish, heat treatment, or special manufacturing processes.
9. Complete Title Block: Fill in all details in the title block.
10. Check and Verify: Review the drawing for completeness, accuracy, clarity, and adherence to drawing standards.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Practical Activity

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Recalling/Motivation

Teacher’s Activity: The teacher greets the students and reviews the previous lesson on orthographic projection. The teacher then asks students about the importance of accurate drawings in engineering and introduces the topic of engineering working drawings of machine parts.

Pupils’ Activity: Pupils respond to questions about orthographic projection and listen attentively to the introduction of the new topic.

Learning Point: Importance of accurate drawings

Step 2: Explanation of Engineering Working Drawings

Time: 10 minutes

Teaching Skill: Explanation/Illustration

Teacher’s Activity: The teacher explains what engineering working drawings are and discusses their key features, such as orthographic views, dimensions, and material specifications. The teacher uses sample drawings to illustrate these features.

Pupils’ Activity: Pupils listen, observe the sample drawings, and ask questions for clarification.

Learning Point: Features of working drawings

Step 3: Identification of Machine Parts

Time: 10 minutes

Teaching Skill: Identification/Demonstration

Teacher’s Activity: The teacher presents actual machine parts (e.g., a simple bracket, sleeve, cylinder, crank, pedal) or their models. The teacher guides students to identify these parts and discuss their basic functions and shapes, relating them to the need for working drawings.

Pupils’ Activity: Pupils identify the machine parts, discuss their functions, and observe their shapes.

Learning Point: Common machine parts

Step 4: Principles for Drawing Brackets

Time: 10 minutes

Teaching Skill: Demonstration/Guidance

Teacher’s Activity: The teacher demonstrates how to prepare a working drawing of a simple bracket. This includes selecting appropriate views (front, top, side), sketching the outlines, adding hidden lines, and applying correct dimensions. The teacher emphasizes clarity and standard conventions.

Pupils’ Activity: Pupils observe the demonstration, ask questions, and make preliminary sketches in their notebooks.

Learning Point: Drawing principles for brackets

Step 5: Principles for Drawing Sleeves and Cylinders

Time: 5 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher briefly explains and demonstrates the specific considerations for drawing sleeves and cylinders, focusing on representing circular features, internal bores, and length dimensions accurately in orthographic views.

Pupils’ Activity: Pupils observe the demonstration and note key points for drawing cylindrical parts.

Learning Point: Drawing cylindrical parts

Step 6: Guided Practice on a Simple Machine Part

Time: 5 minutes

Teaching Skill: Guided Practice/Supervision

Teacher’s Activity: The teacher guides students to begin preparing a working drawing of a simple machine part, such as a crank or pedal, using their drawing instruments. The teacher circulates to provide individual assistance and correct errors.

Pupils’ Activity: Pupils start drawing the given machine part under the teacher’s guidance, applying the principles learned.

Learning Point: Practical drawing application

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. What is the main purpose of an engineering working drawing?
2. Mention two essential elements found in a complete working drawing.
3. Name three machine parts that typically require working drawings.
4. Why is accurate dimensioning important in a working drawing?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding working drawings

Step 8: Note-Taking

Time: 10 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on engineering working drawings and examples of machine parts into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Recording lesson content

Step 9: Conclusion

Time: 5 minutes

Teaching Skill: Consolidation

Teacher’s Activity: The teacher summarises the key points of the lesson, reiterating the importance of precision and adherence to standards in preparing engineering working drawings for various machine parts. The teacher encourages students to practice regularly.

Pupils’ Activity: Pupils listen to the summary and prepare for the next lesson.

Learning Point: Reinforcing drawing importance

Continuous Assessment/Further Study

Type: Homework/Practice Exercise

Instruction: Using appropriate drawing instruments, prepare a complete engineering working drawing for one of the following simple machine parts. Ensure all necessary orthographic views and dimensions are included.

1. A simple cylindrical shaft with a keyway.
2. A flanged sleeve.
3. A rectangular support bracket with two holes.

Lesson Keywords

• Working Drawing – A detailed technical drawing providing all information for manufacturing.
• Orthographic Projection – Method of representing 3D objects in 2D views.
• Dimensioning – Adding numerical values to indicate size and location.
• Bracket – A supporting machine part, often L-shaped.
• Sleeve – A cylindrical component, often hollow, used for enclosure or connection.
• Cylinder – A basic geometric shape, common in machine parts like shafts or pins.
• Tolerances – Permissible variations in dimensions.

Differentiation

For students who grasp the concepts quickly, the teacher can provide more complex machine parts to draw or challenge them to include sectional views and surface finish symbols. For students needing additional support, the teacher can provide pre-drawn outlines for simpler parts, focusing on correct dimensioning and line types, and offer more one-on-one guidance during the practical activity.

Suggested Lesson Videos

Search YouTube for: “Engineering working drawings basics”, “Technical drawing machine parts SS3”, “How to draw orthographic views of a bracket”