Engineering Working Drawings of Machine Parts for SS 3

Class: SS 3
Term: First Term
Week: 6
Age: 17 years
Duration: 60 minutes
Subject: Technical Drawing
Curriculum Theme: Engineering Drawing
Previous Lesson: Engineering Working Drawings of Brackets, Sleeves and Cylinders
Topic: ENGINEERING WORKING DRAWINGS OF MACHINE PARTS
Subject Matter: Example of machine parts rod etc

Specific Objectives

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

Cognitive Domain

• Define engineering working drawings.
• Identify common machine parts such as piston, connecting rod, and crank.
• State the purpose of engineering working drawings.

Psychomotor Domain

• Prepare orthographic views of simple machine parts like a piston.
• Prepare orthographic views of a connecting rod.
• Prepare orthographic views of a crank.
• Apply correct dimensioning techniques to working drawings.

Affective Domain

• Appreciate the importance of precision and accuracy in technical drawing.
• Develop an interest in the application of technical drawing in mechanical engineering.

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:

• Models of a piston, connecting rod, and crank
• Drawing board
• T-square
• Set squares (45° and 30°/60°)
• Drawing pencils (HB, H, 2H)
• Eraser
• Drawing paper
• Dividers and compasses
• Protractor
• Dimensioning rules and standards charts

Rationale for the Lesson

This lesson is important as it provides students with practical skills in creating detailed technical drawings, which are fundamental for communication in engineering and manufacturing industries. Understanding working drawings enables students to interpret and produce designs accurately, bridging the gap between design concepts and physical production.

Prerequisite/Previous Knowledge

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

Lesson Content/Board Summary

ENGINEERING WORKING DRAWINGS OF MACHINE PARTS

What are Engineering Working Drawings?

Engineering working drawings are detailed graphical representations of components or assemblies used in manufacturing and construction. They serve as a universal language for engineers, designers, and manufacturers to communicate precise design information.

Their primary purpose is to provide all the necessary information for a part to be manufactured or an assembly to be put together correctly. This information includes:

1. Geometric features (shapes, sizes).
2. Dimensions and tolerances.
3. Material specifications.
4. Surface finishes.
5. Manufacturing processes.

Key Features of Engineering Working Drawings

A complete engineering working drawing typically includes several key elements to ensure clarity and accuracy:

1. Orthographic Views: Multiple 2D views (e.g., front, top, side) arranged according to first-angle or third-angle projection to show the object from different perspectives.
2. Dimensions: Numerical values indicating the size and location of features, including lengths, widths, heights, diameters, radii, and angles.
3. Tolerances: Permissible variations in dimensions or geometric features, indicating the acceptable range for manufacturing.
4. Material Specifications: Information about the material from which the part is to be made (e.g., steel, aluminium, plastic).
5. Surface Finish Symbols: Indications of the required smoothness or texture of a surface.
6. Title Block: A standard block containing essential information such as the drawing title, part number, scale, date, designer, and material.
7. Part List/Bill of Materials (BOM): For assemblies, a list of all individual components with their quantities and descriptions.

Examples of Machine Parts and their Working Drawings

Working drawings are essential for producing various machine parts. Here are examples of common machine parts and the elements typically shown in their working drawings:

Piston

A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings.

Elements of a working drawing for a piston typically include:

1. Views: Often a full or half-sectioned front view to show internal features (e.g., piston pin bore, ring grooves), a side view, and sometimes a top view.
2. Critical Dimensions: Piston diameter, height, piston pin bore diameter, width and depth of ring grooves, combustion bowl shape (if applicable).
3. Material: Usually aluminium alloy or cast iron.
4. Tolerances: Tight tolerances for diameter and pin bore to ensure proper fit and function.

Connecting Rod

A connecting rod connects the piston to the crankshaft, converting the reciprocating motion of the piston into the rotary motion of the crankshaft. It is subjected to significant compressive and tensile forces.

Elements of a working drawing for a connecting rod typically include:

1. Views: Front view (often sectioned through the big end and small end), and a side view.
2. Critical Dimensions: Centre-to-centre length between the big end and small end bores, big end bore diameter, small end bore diameter, width of both ends, beam cross-section dimensions.
3. Material: Typically forged steel.
4. Tolerances: Close tolerances for bore diameters and parallelism between the bores.

Crank

A crank is a part of a crankshaft, which is a mechanical part able to perform a conversion between reciprocating motion and rotational motion. In a reciprocating engine, it translates the linear reciprocating motion of the piston into rotational motion.

Elements of a working drawing for a crank (part of a crankshaft) typically include:

1. Views: Front view, top view, and side view to fully define its complex geometry.
2. Critical Dimensions: Crank radius (throw), main journal diameters, crankpin diameter, web thickness and shape, overall length.
3. Material: Typically forged steel or cast iron.
4. Tolerances: Very tight tolerances on journal diameters, runout, and balance to ensure smooth engine operation.

Teaching Methods/Instructional Techniques

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

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Questioning/Review

Teacher’s Activity: The teacher greets the students and reviews the previous lesson on orthographic projection. The teacher then introduces the new topic by asking students what they think engineers use to communicate designs for manufacturing machine parts.

Pupils’ Activity: Pupils respond to questions about orthographic projection and offer ideas on how designs are communicated.

Learning Point: Introduction to topic

Step 2: Explanation of Engineering Working Drawings

Time: 10 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains what engineering working drawings are, their purpose, and their importance in mechanical engineering and manufacturing. The teacher shows examples of simple working drawings (if available) or sketches on the board.

Pupils’ Activity: Pupils listen attentively, ask questions for clarification, and observe the examples.

Learning Point: Meaning of working drawings

Step 3: Identifying Machine Parts

Time: 10 minutes

Teaching Skill: Demonstration/Identification

Teacher’s Activity: The teacher presents the physical models of a piston, connecting rod, and crank. The teacher identifies each part, explains its basic function, and points out key features relevant to drawing them.

Pupils’ Activity: Pupils observe the models, identify the parts, and listen to their functions.

Learning Point: Identification of machine parts

Step 4: Discussing Features of Working Drawings

Time: 10 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher discusses the key features that must be included in a complete working drawing, such as orthographic views, dimensions, tolerances, and material specifications, relating them to the machine parts shown.

Pupils’ Activity: Pupils participate in the discussion, asking how each feature contributes to the drawing’s completeness.

Learning Point: Features of working drawings

Step 5: Guided Practice – Piston Working Drawing

Time: 10 minutes

Teaching Skill: Guided Practice/Demonstration

Teacher’s Activity: The teacher guides students through preparing a basic working drawing of the piston. The teacher demonstrates how to set up the drawing sheet, draw the main orthographic views (e.g., front sectioned view, side view), and add essential dimensions.

Pupils’ Activity: Pupils follow the teacher’s instructions, sketching the piston’s views and adding dimensions on their drawing paper.

Learning Point: Piston drawing practice

Step 6: Guided Practice – Connecting Rod and Crank Working Drawings

Time: 5 minutes

Teaching Skill: Guided Practice/Supervision

Teacher’s Activity: The teacher provides brief guidance on how to approach the working drawings for the connecting rod and crank, highlighting specific views and critical dimensions. The teacher encourages students to attempt these drawings.

Pupils’ Activity: Pupils begin sketching the connecting rod and crank, applying the principles learned.

Learning Point: Connecting rod and crank drawing

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 an engineering working drawing?
2. Mention two key features of a complete working drawing.
3. Name three machine parts discussed today.
4. Why is precision important in technical 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, including definitions, features, 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 lesson by reiterating the importance of engineering working drawings as a communication tool in engineering and encourages students to practice drawing various machine parts to improve their skills.

Pupils’ Activity: Pupils listen and ask any final questions.

Learning Point: Reinforcement of concepts

Continuous Assessment/Further Study

Type: Homework/Practice Exercise

Instruction: On a clean drawing sheet, prepare a complete working drawing for one of the following simple machine parts, ensuring all necessary views, dimensions, and a title block are included:

1. A simple shaft with a keyway.
2. A flanged coupling.
3. A simple bearing housing.

Lesson Keywords

• Engineering Drawing – A technical drawing used to define and communicate design ideas.
• Working Drawing – A detailed technical drawing providing all information for manufacturing or assembly.
• Machine Parts – Individual components that make up a machine, such as pistons, rods, and cranks.
• Orthographic Projection – A method of representing 3D objects in 2D views.
• Dimensioning – The process of adding numerical values to a drawing to indicate sizes and locations.
• Piston – A component of reciprocating engines that transmits force.
• Connecting Rod – Links the piston to the crankshaft.
• Crank – Part of a crankshaft that converts motion.

Differentiation

For students who grasp the concepts quickly, the teacher can challenge them to include more complex features like sectional views, auxiliary views, or apply specific geometric dimensioning and tolerancing (GD&T) principles. For students who need more support, the teacher can provide simplified drawing exercises, pre-drawn templates, or offer one-on-one guidance during the practical activity, focusing on basic views and dimensioning.

Suggested Lesson Videos

For further understanding, search on YouTube for:

• Engineering Working Drawings Machine Parts SS3
• how to draw piston technical drawing
• connecting rod technical drawing