Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 1st Term
Week: 10
Age: 16 years
Duration: 45 minutes
Subject: Metal Work
Curriculum Theme: Pre-Vocational Studies
Previous Lesson: Welding Joints and Defects.
Topic: Temporary Joining Process (Screw Thread)
Subject Matter: Meaning of screw thread (mechanical fastening system), screw thread terms, parts of external screw thread, uses of screw thread, production of screw thread (hand tools, machine tools)

Specific Objectives

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

Cognitive Domain:

Define screw thread as a mechanical fastening system.
Identify and explain common screw thread terms.
List various uses of screw threads in daily life and industry.
Differentiate between hand tools and machine tools used for screw thread production.

Affective Domain:

Appreciate the importance of screw threads in temporary joining.
Show interest in the proper handling and use of threading tools.

Psychomotor Domain:

Sketch the basic parts of an external screw thread.
Identify the hand tools used for cutting external and internal threads.

Participate actively in class discussions about screw threads.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Schools Education Curriculum
State Unified Scheme of Work
Basic Metal Work Technology for Senior Secondary Schools, by A.O. Okoro

Instructional Materials

The teacher will teach this lesson with the aid of:

Lathe machine
Mild steel rod
Threading tools (dies, taps, die stock, tap wrench, cutting oil)
Charts illustrating screw thread terms and parts

Rationale for the Lesson

This lesson helps pupils understand the principles of temporary joining through screw threads, which are essential in assembling and disassembling mechanical components. It enables them to recognize various screw thread applications and the tools involved in their production, which is important for practical skills development.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of metal joining methods, common workshop hand tools, and fundamental machining operations.

Lesson Content/Board Summary

Temporary Joining Process: Screw Thread

Meaning of Screw Thread

A screw thread is a helical structure used to convert rotational motion into linear motion or to provide a fastening mechanism. It is a ridge of uniform section in the form of a helix on the external or internal surface of a cylinder or cone. Screw threads are a common mechanical fastening system.

Screw Thread Terms

The following are common terms associated with screw threads:

Major Diameter: The largest diameter of a screw thread, measured from crest to crest.
Minor Diameter: The smallest diameter of a screw thread, measured from root to root.
Pitch: The distance between corresponding points on adjacent threads, measured parallel to the axis.
Crest: The top surface of a thread.
Root: The bottom surface of the thread valley.
Flank: The surface between the crest and the root.
Thread Angle: The angle included between the flanks of the thread measured in an axial plane.
Lead: The axial distance a screw advances in one complete revolution. For single-start threads, lead equals pitch.

Parts of an External Screw Thread

An external screw thread (on a bolt or shaft) consists of a cylindrical body with a continuous helical ridge. Key parts include the major diameter (outermost), minor diameter (innermost), crests (peaks), roots (valleys), and flanks (sloping sides) which form the thread angle.

Uses of Screw Thread

The following are common uses of screw threads:

For fastening components together (e.g., bolts, nuts, screws).
For transmitting power and motion (e.g., lead screws in lathes, screw jacks).
For making adjustments and precise movements (e.g., micrometers, valves).
For creating fluid-tight seals (e.g., pipe threads).

Production of Screw Thread

Screw threads can be produced using hand tools or machine tools.

Hand Tools for Screw Thread Production

Hand tools are used for cutting threads manually, typically for smaller jobs or repairs.

Dies: Used for cutting external threads on rods or bolts.
Die Stock (Handle): Holds the die for manual rotation.
Taps: Used for cutting internal threads in holes.
Tap Wrench (Handle): Holds the tap for manual rotation.
Cutting Oil: Used to lubricate the cutting process and improve thread quality.

Machine Tools for Screw Thread Production

Machine tools provide greater accuracy, speed, and are suitable for mass production.

Lathe Machine: Used for cutting external and internal threads on cylindrical workpieces with high precision. The workpiece rotates while a single-point cutting tool moves axially.
Thread Milling Machine: Uses a rotating cutter to mill threads.
Thread Grinding Machine: Used for producing highly accurate threads, often after hardening.
Rolling Machine: Forms threads by plastically deforming the material, rather than cutting it, making stronger threads.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them to identify objects in the classroom that are joined together temporarily and can be easily disassembled, such as furniture held by bolts or screws.
Pupils’ Activity: Pupils identify objects like desks, chairs, and doors, mentioning screws and bolts as joining methods.
Learning Point: Pupils recall prior knowledge of temporary joining methods.

Step 2: Meaning of Screw Thread

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher defines screw thread as a helical structure used for fastening or motion transmission, showing a diagram or actual bolt.
Pupils’ Activity: Pupils listen attentively and attempt to define screw thread in their own words.
Learning Point: Pupils understand the basic concept of a screw thread.

Step 3: Screw Thread Terms and Parts

Time: 10 minutes
Teaching Skill: Illustration/Explanation
Teacher’s Activity: The teacher uses a chart or a large model of a screw thread to explain and label terms such as major diameter, minor diameter, pitch, crest, root, and flank.
Pupils’ Activity: Pupils observe the chart, listen to the explanations, and identify the parts and terms.
Learning Point: Pupils learn and identify the specific parts and terminology of a screw thread.

Step 4: Uses of Screw Thread

Time: 5 minutes
Teaching Skill: Discussion
Teacher’s Activity: The teacher leads a discussion on various applications of screw threads, asking pupils to give examples from everyday life and industry.
Pupils’ Activity: Pupils contribute examples like bolts, nuts, bottle caps, and car jacks.
Learning Point: Pupils understand the practical importance and wide range of uses for screw threads.

Step 5: Production of Screw Thread (Hand Tools)

Time: 8 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher explains and demonstrates the use of hand tools (dies, die stock, taps, tap wrench) for cutting external and internal threads, highlighting safety precautions.
Pupils’ Activity: Pupils observe the demonstration and ask questions about the tools and process.
Learning Point: Pupils learn about hand tools and their application in thread cutting.

Step 6: Production of Screw Thread (Machine Tools)

Time: 7 minutes
Teaching Skill: Explanation/Visualisation
Teacher’s Activity: The teacher explains how screw threads are produced using machine tools, specifically focusing on the lathe machine and its operation for threading, using pictures or a video if available.
Pupils’ Activity: Pupils listen and differentiate between hand and machine methods of thread production.
Learning Point: Pupils understand the principles of machine threading and recognize common machine tools.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

What is a screw thread?
List any three terms associated with screw threads.
Mention two uses of screw threads.
State two hand tools used for cutting threads.
How is threading done on a lathe machine?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson and assigns homework, asking pupils to draw and label the parts of an external screw thread.
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: Pupils consolidate their understanding and prepare for further study.

Lesson Keywords

Screw Thread – A helical ridge on a cylinder or cone used for fastening or motion.
Major Diameter – The largest diameter of a screw thread.
Pitch – The distance between adjacent threads.
Die – A hand tool used to cut external threads.
Tap – A hand tool used to cut internal threads.
Lathe Machine – A machine tool used for cutting threads precisely.

Differentiation

For pupils who grasp concepts quickly, the teacher can encourage them to research different types of screw threads (e.g., metric, imperial, Acme) and their specific applications. For pupils needing more support, the teacher will provide simplified diagrams and allow more time for identifying parts and terms, offering one-on-one guidance.

Note for teachers using this lesson plan

Teachers should ensure that actual threading tools and, if possible, a functional lathe machine are available for demonstration. Safety precautions during tool handling and machine operation must be emphasized. Encourage pupils to relate the lesson to practical examples they encounter daily.