Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 1st Term
Week: 6
Age: 15 years
Duration: 45 minutes
Subject: Wood Work
Curriculum Theme: Vocational Studies
Previous Lesson: Structure of Wood Cells and Timber Characteristics.
Topic: TIMBER CONVERSION METHODS
Subject Matter: through and through sawing, tangential sawing, radial sawing, saw milling

Specific Objectives

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

Cognitive Domain:

Define timber conversion.
State reasons for converting timber.
Identify different methods of timber conversion.
Explain the process of saw milling.

Affective Domain:

Appreciate the importance of proper timber conversion techniques.
Show interest in observing various timber conversion methods.

Psychomotor Domain:

Describe the characteristics of timber converted by different methods.
Differentiate between through and through, tangential, and radial sawing.

Discuss the socio-economic benefits of saw milling to the community.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Senior Secondary School (Wood Work)
State Unified Scheme of Work for SSS 1 Wood Work
F.O. Ojo. (2010). Woodwork Technology for Senior Secondary Schools. Evans Brothers (Nigeria Publishers) Limited.

Instructional Materials

The teacher will teach this lesson with the aid of:

Charts showing different timber conversion methods.
Actual timber samples demonstrating various cuts.
Diagrams illustrating saw milling processes.
A visit to a local sawmill (if feasible).

Rationale for the Lesson

This lesson helps pupils understand how logs are processed into usable timber. Knowing the different conversion methods is important for selecting the right type of wood for various construction and carpentry purposes, which is a practical skill in daily life.

Prerequisite/Previous Knowledge

Pupils have basic knowledge of wood as a material, its sources, and general uses in construction and furniture making.

Lesson Content/Board Summary

TIMBER CONVERSION METHODS

Definition of Timber Conversion

Timber conversion is the process of cutting logs into desired sizes and shapes of planks, boards, or other forms suitable for various uses.

Reasons for Timber Conversion

The following are reasons for converting timber:

To reduce the weight of the timber for easier transportation.
To facilitate seasoning (drying) of the wood.
To reduce waste and maximize usable portions of the log.
To produce timber of desired dimensions and shapes for specific purposes.
To remove defects such as knots and shakes.

Methods of Timber Conversion

There are several methods used for timber conversion, primarily involving different sawing patterns:

Through and Through Sawing: This is the simplest and most common method. The log is sawn into planks by making parallel cuts from one end to the other without turning the log. It produces wide boards but is prone to warping.
Tangential Sawing (Flat Sawing/Plain Sawing): Cuts are made parallel to the tangent of the annual rings. This method yields boards with prominent grain patterns but can result in more shrinkage and warping across the width.
Radial Sawing (Quarter Sawing): The log is first cut into quarters, and then each quarter is sawn perpendicular to the annual rings. This method produces stable timber with attractive grain patterns (quarter-sawn grain), less prone to warping and shrinking, but it is more wasteful and slower.
Saw Milling: This refers to the entire operation of converting logs into lumber using various types of saws and machinery in a sawmill. It encompasses all the sawing methods described above on an industrial scale.

Saw Milling Process

The saw milling process generally involves the following steps:

Log Debarking: Removing the bark from the logs.
Primary Breakdown: Initial cutting of the log into large sections or cants using head saws (e.g., band saws, circular saws).
Secondary Breakdown: Further cutting of cants into boards and planks of specific dimensions using re-saws.
Edging: Trimming the rough edges of boards to create straight, parallel sides.
Trimming: Cutting boards to their final lengths and removing defects.
Grading: Inspecting and classifying the timber based on quality and intended use.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids, Excursion/Field Trip

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them to recall what they know about wood and how it is obtained from trees. The teacher then introduces the topic: “Timber Conversion Methods,” explaining that today’s lesson will focus on how logs are cut into usable timber.
Pupils’ Activity: Pupils respond to questions about wood and listen attentively to the introduction.
Learning Point: Pupils are prepared for the lesson and connect new knowledge to previous understanding.

Step 2: Definition of Timber Conversion

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines timber conversion as the process of cutting logs into planks, boards, or other desired forms. The teacher writes the definition on the board.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the meaning of timber conversion.

Step 3: Reasons for Timber Conversion

Time: 7 minutes
Teaching Skill: Explanation/Listing
Teacher’s Activity: The teacher explains the various reasons why timber needs to be converted, such as reducing weight, facilitating seasoning, minimizing waste, and producing specific dimensions. The teacher lists these points on the board.
Pupils’ Activity: Pupils listen, contribute ideas if prompted, and write down the reasons.
Learning Point: Pupils identify the importance and purposes of timber conversion.

Step 4: Methods of Timber Conversion

Time: 10 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher explains and illustrates the three main methods of timber conversion: through and through sawing, tangential sawing, and radial sawing, using charts, diagrams, and actual timber samples. If a sawmill visit was conducted, the teacher relates the explanation to observations made during the visit.
Pupils’ Activity: Pupils observe the illustrations and samples, listen to explanations, and ask questions to differentiate between the methods.
Learning Point: Pupils learn and differentiate between the various timber conversion methods.

Step 5: Saw Milling Process

Time: 6 minutes
Teaching Skill: Explanation/Sequencing
Teacher’s Activity: The teacher explains the general steps involved in the saw milling process, from debarking to grading, highlighting the industrial aspect of timber conversion. The teacher lists the steps on the board.
Pupils’ Activity: Pupils listen, take notes, and discuss how these steps relate to the overall conversion.
Learning Point: Pupils understand the sequence of operations in a sawmill.

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 timber conversion.
Mention three reasons why timber is converted.
List and briefly explain two methods of timber conversion.
Outline any three steps involved in the saw milling process.

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/Consolidation
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the definition, reasons, and methods of timber conversion. The teacher assigns homework: “Draw and label diagrams illustrating through and through sawing and radial sawing.”
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: Pupils consolidate their learning and are given an opportunity for further practice.

Lesson Keywords

Timber Conversion – The process of cutting logs into usable forms.
Through and Through Sawing – A method where logs are sawn into parallel planks without turning.
Tangential Sawing – A method where cuts are made parallel to the tangent of the annual rings.
Radial Sawing – A method where logs are quartered and then sawn perpendicular to the annual rings.
Saw Milling – The industrial process of converting logs into lumber.

Differentiation

For pupils who grasp concepts quickly, the teacher can encourage them to research the advantages and disadvantages of each sawing method in more detail. For pupils needing more support, the teacher will provide additional visual aids and simplified explanations, ensuring they can identify and define the basic methods.

Note for teachers using this lesson plan

Teachers should ensure that charts and diagrams are clear and visible to all pupils. If a sawmill visit is not feasible, consider showing videos or detailed pictures of the processes. Emphasize the practical applications of each conversion method in carpentry and construction.