Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 1st Term
Week: 11
Age: 16 years
Duration: 45 minutes
Subject: Metal Work
Curriculum Theme: Pre-Vocational Studies
Previous Lesson: Screw Threads and Mechanical Fasteners.
Topic: Forms of Screw Thread
Subject Matter: Forms of screw thread (square thread, ACME thread, buttress thread), applications of different thread forms

Specific Objectives

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

Cognitive Domain:

Define different forms of screw threads such as square, ACME, and buttress threads.
Identify the characteristics of each thread form.
Explain the specific applications of each thread form.

Affective Domain:

Appreciate the importance of selecting the correct screw thread for specific applications.
Value the precision required in manufacturing and using screw threads.

Psychomotor Domain:

Sketch the different forms of screw threads.
Propose suitable thread forms for various practical scenarios.

Collaborate in identifying the uses of different screw threads in daily life.

Reference Materials

The following resources were used in planning this lesson:

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

Instructional Materials

The teacher will teach this lesson with the aid of:

Thread charts
Metal samples with different screw threads
Whiteboard and markers

Rationale for the Lesson

This lesson helps pupils understand the various types of screw threads and their unique features. Knowing different thread forms enables pupils to select the appropriate thread for specific mechanical applications, which is essential in metalwork and engineering.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of fasteners, tools, and general workshop safety.

Lesson Content/Board Summary

Forms of Screw Thread

Introduction to Screw Threads

A screw thread is a helical structure used to convert rotational motion into linear motion or to provide a fastening mechanism. Different forms of screw threads are designed for specific purposes based on their strength, efficiency, and direction of load.

Square Thread

The square thread has a thread angle of 0 degrees, meaning its flanks are perpendicular to the axis of the screw. It has a high efficiency in transmitting power due to the absence of radial components of force.

The following are applications of square thread:

Screw jacks
Presses
Clamping devices
Heavy load power transmission

ACME Thread

The ACME thread is a trapezoidal thread form with a 29-degree included angle. It is a modification of the square thread, offering better strength and ease of machining while maintaining good power transmission efficiency.

The following are applications of ACME thread:

Lead screws of lathes
Vices
Clamps
Valve stems
Power transmission in machine tools

Buttress Thread

The buttress thread is an asymmetric thread form, typically with one flank perpendicular to the screw axis (0-degree angle) and the other flank inclined (often 45 degrees). This design makes it very strong in transmitting heavy axial thrust in only one direction.

The following are applications of buttress thread:

Vices
C-clamps
Gun breeches
Jacking screws
Where heavy loads are applied in a single direction

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 name different types of fasteners they know. The teacher then introduces the topic “Forms of Screw Thread” and states the learning objectives.
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively to the introduction.
Learning Point: Pupils are introduced to the topic and understand the learning goals.

Step 2: Square Thread

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher uses thread charts and metal samples to explain the characteristics of the square thread. The teacher also discusses its applications.
Pupils’ Activity: Pupils observe the charts and samples, ask questions, and take notes.
Learning Point: Pupils understand the definition and uses of square threads.

Step 3: ACME Thread

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the ACME thread, highlighting its trapezoidal shape and 29-degree angle. The teacher then demonstrates its typical applications using examples or diagrams.
Pupils’ Activity: Pupils listen, observe the instructional materials, and copy notes.
Learning Point: Pupils learn about the ACME thread and its specific uses.

Step 4: Buttress Thread

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher describes the buttress thread, emphasizing its asymmetric design and its strength in one direction. The teacher provides examples of where it is used.
Pupils’ Activity: Pupils pay attention, interact with the teacher, and write down key points.
Learning Point: Pupils grasp the concept of buttress thread and its directional load-bearing capability.

Step 5: Comparative Discussion and Sketching

Time: 6 minutes
Teaching Skill: Guided Practice
Teacher’s Activity: The teacher leads a brief discussion comparing the three thread forms, prompting pupils to identify their differences and similarities. The teacher then guides pupils to sketch the thread forms.
Pupils’ Activity: Pupils participate in the discussion and attempt to sketch the different thread forms in their notebooks.
Learning Point: Pupils reinforce their understanding by comparing threads and practicing drawing them.

Step 6: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

Define a square thread.
List two applications of ACME thread.
What is the main characteristic of a buttress thread?
State one difference between a square thread and an ACME thread.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 7: Conclusion

Time: 5 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the importance of understanding different screw thread forms for practical applications in metalwork.
Pupils’ Activity: Pupils listen to the summary and ask any remaining questions.
Learning Point: Pupils consolidate their knowledge of the topic.

Lesson Keywords

Screw Thread – A helical ridge on a cylindrical or conical surface, used for fastening or power transmission.
Square Thread – A thread form with flanks perpendicular to the screw axis, used for heavy load transmission.
ACME Thread – A trapezoidal thread form with a 29-degree angle, used for lead screws and power transmission.
Buttress Thread – An asymmetric thread form, strong in one direction, used for heavy axial thrust.
Fasteners – Devices used to mechanically join or affix two or more objects together.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to identify more complex applications or design scenarios for each thread type. For those needing extra support, the teacher can provide pre-drawn outlines of the threads for tracing or simpler identification tasks.

Note for teachers using this lesson plan

Ensure that actual physical samples of different screw threads are available for pupils to observe and handle. Encourage pupils to relate the lesson to real-world applications they encounter in their environment. Emphasize safety when handling metal samples.