Engineering Working Drawings of Parallel Clamps and Water Taps for SS 3

Class: SS 3
Term: First Term
Week: 7
Age: 17 years
Duration: 60 minutes
Subject: Technical Drawing
Curriculum Theme: Engineering Working Drawings
Previous Lesson: Engineering Working Drawings of Machine Parts
Topic: ENGINEERING WORKING DRAWINGS
Subject Matter: Machine assemblies e.g. parallel clamps, water taps

Specific Objectives

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

Cognitive Domain

• Define engineering working drawings for assemblies.
• State the key principles of assembly drawing.
• Identify the main components of a parallel clamp.
• Identify the main components of a water tap.

Psychomotor Domain

• Prepare a working drawing of a parallel clamp assembly.
• Prepare a working drawing of a water tap assembly.
• Incorporate bolts and nuts correctly into assembly drawings.

Affective Domain

• Appreciate the importance of accuracy and detail in technical drawing.
• Develop an interest in the practical application of technical drawing skills.

Reference Materials

The following resources were used in planning this lesson:

• 2014 Senior Secondary Education Curriculum (SSEC)
• Relevant State Unified Scheme of Work
• A suitable Technical Drawing textbook for SS3
• FCT ERC/NAPPS Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Actual parallel clamps
• Actual water taps
• Drawing instruments (T-square, set squares, compass, protractor, drawing pencils, eraser)
• Drawing sheets
• Diagrams or charts showing exploded views and assembled views of parallel clamps and water taps

Rationale for the Lesson

This lesson is essential as it equips students with the practical skill of creating engineering working drawings for machine assemblies. Understanding how to represent assembled components, including fasteners, is fundamental for effective communication in engineering design, manufacturing, and maintenance. It provides a solid foundation for students pursuing careers in technical and engineering fields.

Prerequisite/Previous Knowledge

Students should have a basic understanding of orthographic projection, sectional views, dimensioning, and the drawing of individual machine components.

Lesson Content/Board Summary

ENGINEERING WORKING DRAWINGS

Meaning of Engineering Working Drawings

Engineering working drawings are detailed graphical representations that provide all the necessary information for manufacturing, assembling, and inspecting a product or component. For machine assemblies, these drawings show how individual parts fit together to form a complete functional unit.

Principles of Assembly Drawing

Assembly drawings illustrate the complete product with all its components in their correct relative positions. Key principles include:

1. Overall View: Showing the entire assembly in one or more orthographic views (e.g., front, top, side views).
2. Identification of Parts: Each component is identified, often with part numbers or balloons linked to a parts list or bill of materials.
3. Hidden Lines: Used sparingly to avoid clutter, often replaced by sectional views.
4. Sectional Views: Frequently used to reveal internal construction and how parts mate.
5. Dimensioning: Overall dimensions and critical assembly dimensions are provided, but individual part dimensions are usually left to detail drawings.
6. Fasteners: Standard fasteners like bolts, nuts, and screws are typically shown in their simplified or conventional representations.
7. Exploded Views: Sometimes included to show the order of assembly and how parts relate to each other before assembly.

Components and Assembly Drawing of a Parallel Clamp

Components of a Parallel Clamp

A parallel clamp is a device used to hold workpieces securely. Its typical components include:

1. Fixed Jaw: The stationary part of the clamp.
2. Sliding Jaw: The movable part that adjusts to grip the workpiece.
3. Screw (Spindle): A threaded rod that moves the sliding jaw.
4. Handle/Knob: Used to turn the screw.
5. Guide Bar(s): Rods that ensure the sliding jaw moves parallel to the fixed jaw.
6. Nut/Collar: Often integrated into the fixed jaw or a separate component to engage the screw.

Steps for Drawing a Parallel Clamp Assembly

To prepare a working drawing of a parallel clamp assembly:

1. Understand the Assembly: Study the actual clamp or its exploded view to understand how each part fits.
2. Select Views: Choose appropriate orthographic views (e.g., front view, top view, side view) to clearly show the assembly. A sectional view is often useful.
3. Draw Major Components: Start by drawing the fixed jaw, then position the sliding jaw relative to it.
4. Add Fasteners and Moving Parts: Incorporate the screw, handle, and guide bars in their assembled positions.
5. Apply Conventional Representations: Use standard symbols for threads, bolts, and nuts.
6. Dimensioning: Add overall dimensions and any critical assembly dimensions.
7. Parts List: Create a bill of materials (BOM) listing each component, its quantity, and material.
8. Title Block: Complete the drawing with a title block containing relevant information (e.g., drawing title, scale, date, name).

Components and Assembly Drawing of a Water Tap

Components of a Water Tap

A water tap (faucet) controls the flow of water. Common components include:

1. Body/Casing: The main housing of the tap, often made of brass or chrome-plated metal.
2. Spout: The part from which water flows.
3. Handle/Knob: Used to turn the tap on or off.
4. Valve Stem: A threaded rod connected to the handle, which moves the washer.
5. Washer/Disc: A rubber or ceramic component that seals against the valve seat to stop water flow.
6. Valve Seat: The surface inside the tap body against which the washer presses.
7. Gland Nut/Packing: Seals the valve stem to prevent leaks around the handle.
8. Aerator: (Optional) A mesh screen at the end of the spout to mix air with water.

Steps for Drawing a Water Tap Assembly

To prepare a working drawing of a water tap assembly:

1. Examine the Tap: Disassemble (if possible) or study diagrams to understand the internal mechanism and component arrangement.
2. Choose Views: Select views that best illustrate the internal workings, typically a full or half sectional front view, and a top view.
3. Draw the Body: Begin with the main body of the tap.
4. Assemble Internal Parts: Add the valve stem, washer, valve seat, and gland nut in their correct positions.
5. Attach External Parts: Draw the handle and spout.
6. Show Fasteners: Indicate any internal or external fasteners.
7. Dimensioning: Include overall dimensions and critical assembly dimensions.
8. Parts List and Title Block: Complete with a bill of materials and title block.

Incorporating Bolts and Nuts in Assembly Drawings

Bolts and nuts are common fasteners used to join components in machine assemblies. In working drawings, they are often represented conventionally:

1. Simplified Representation: For clarity, bolts and nuts are usually drawn in a simplified manner, showing their heads, shanks, and threaded portions without intricate thread details.
2. Standard Proportions: Use standard proportions for bolt heads (e.g., hexagonal or square) and nuts relative to the bolt diameter.
3. Sectioning: When a bolt or nut is cut by a section plane, it is conventionally shown unsectioned (not hatched) to indicate that it is a standard part and to avoid obscuring details.
4. Thread Representation: Threads are shown using conventional symbols (e.g., thin lines for major diameter and thick lines for minor diameter, or simplified zig-zag lines).
5. Placement: Ensure bolts and nuts are correctly positioned to show how they secure the assembled parts, passing through clearance holes in the components.

Teaching Methods/Instructional Techniques

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

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Elicitation/Motivation

Teacher’s Activity: The teacher displays actual parallel clamps and water taps, asking students to identify them and discuss their purpose. The teacher then introduces the topic of engineering working drawings for machine assemblies, linking it to the importance of showing how parts fit together.

Pupils’ Activity: Pupils identify the items and share their thoughts on their function. They listen attentively to the introduction.

Learning Point: Introduction to assembly drawings

Step 2: Meaning of Engineering Working Drawings

Time: 5 minutes

Teaching Skill: Explanation

Teacher’s Activity: The teacher defines engineering working drawings, specifically focusing on their application to machine assemblies and their purpose in manufacturing and assembly processes.

Pupils’ Activity: Pupils listen and ask clarifying questions about the definition and purpose.

Learning Point: Definition of working drawings

Step 3: Principles of Assembly Drawing

Time: 5 minutes

Teaching Skill: Explanation/Illustration

Teacher’s Activity: The teacher explains the key principles of assembly drawing, such as overall views, identification of parts, use of sectional views, and dimensioning, using diagrams or examples where possible.

Pupils’ Activity: Pupils listen and observe the illustrations, noting the important principles.

Learning Point: Assembly drawing principles

Step 4: Parallel Clamp Assembly Drawing

Time: 10 minutes

Teaching Skill: Demonstration/Guidance

Teacher’s Activity: The teacher disassembles a parallel clamp (or uses an exploded diagram) to show its components. The teacher then demonstrates how to start sketching an assembly drawing of the parallel clamp, highlighting the positioning of major components.

Pupils’ Activity: Pupils observe the components of the parallel clamp and watch the teacher’s demonstration of sketching the assembly.

Learning Point: Parallel clamp assembly drawing

Step 5: Water Tap Assembly Drawing

Time: 10 minutes

Teaching Skill: Demonstration/Guidance

Teacher’s Activity: The teacher disassembles a water tap (or uses an exploded diagram) to show its components. The teacher then demonstrates how to start sketching an assembly drawing of the water tap, emphasizing internal components and sectional views.

Pupils’ Activity: Pupils observe the components of the water tap and watch the teacher’s demonstration of sketching the assembly.

Learning Point: Water tap assembly drawing

Step 6: Incorporating Fasteners and Guided Practice

Time: 10 minutes

Teaching Skill: Demonstration/Guided Practice

Teacher’s Activity: The teacher explains and demonstrates how to incorporate bolts and nuts into the assembly drawings using conventional representations. The teacher then guides students to begin sketching their own assembly drawings of either the parallel clamp or water tap, focusing on correct component placement and fastener representation.

Pupils’ Activity: Pupils practice sketching the assembly drawings, incorporating fasteners under the teacher’s guidance.

Learning Point: Fastener representation and practice

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 primary purpose of an engineering working drawing for an assembly?
2. Mention two key principles to consider when preparing an assembly drawing.
3. Name three main components of a parallel clamp.
4. How are bolts and nuts typically represented in an assembly drawing?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding assembly drawing concepts

Step 8: Note-Taking

Time: 5 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes into their notebooks, ensuring they capture the definitions, principles, and key drawing steps.

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

Learning Point: Recording lesson notes

Step 9: Conclusion

Time: 5 minutes

Teaching Skill: Consolidation

Teacher’s Activity: The teacher briefly summarizes the importance of accurate engineering working drawings for machine assemblies and encourages students to continue practicing their drawing skills. The teacher also addresses any final questions or misconceptions.

Pupils’ Activity: Pupils listen to the summary and ask any remaining questions.

Learning Point: Reinforcement of assembly drawing

Continuous Assessment/Further Study

Type: Homework/Practice Exercise

Instruction: Prepare a detailed working drawing of one of the following machine assemblies, ensuring all components are correctly positioned and fasteners are appropriately represented:

1. A simple bench vice (showing at least three views).
2. A pipe wrench (showing its main components assembled).
3. A G-clamp (showing its frame, screw, and swivel pad).

Lesson Keywords

• Engineering drawing – Detailed graphical representation for manufacturing and assembly.
• Working drawing – A drawing that provides all information needed to manufacture or assemble a part or product.
• Assembly drawing – A drawing showing how individual parts fit together to form a complete unit.
• Parallel clamp – A tool used to hold workpieces, characterized by jaws that remain parallel.
• Water tap – A device for controlling the flow of water from a pipe.
• Bolts – Threaded fasteners used with nuts to join parts.
• Nuts – Internally threaded fasteners used with bolts.
• Fasteners – Devices used to mechanically join two or more objects together.
• Orthographic projection – A method of representing three-dimensional objects in two dimensions.

Differentiation

Support: For students who struggle, provide simplified diagrams or pre-drawn outlines of the main components to trace. Focus on identifying and correctly positioning just two or three key parts in the assembly. Offer one-on-one guidance during the practical sketching session.

Extension: Challenge advanced students to include an exploded view alongside their assembly drawing, or to add more complex sectional views. They could also be tasked with identifying potential design improvements for the given assemblies.

Suggested Lesson Videos

For further understanding and visual demonstrations, students can search on YouTube for:

• “Engineering working drawings assembly”
• “Parallel clamp assembly drawing tutorial”
• “Water tap sectional view drawing”