Class: Senior Secondary School 2 (SS2 / SSS 2)
Term: Third Term
Week: 8
Age: 16 years
Duration: 45 minutes
Subject: Metal Work
Curriculum Theme: Pre-Vocational Studies
Previous Lesson: Lathe Machine and Operations.
Topic: Lathe Cutting Tools
Subject Matter: Lathe cutting tools (right hand tool, left hand tool, slotting tool), tool holders, cutting speed for lathe

Specific Objectives

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

Cognitive Domain:

Define lathe cutting tools.
Identify different types of lathe cutting tools and their uses.
State the formula for calculating cutting speed.
List factors affecting cutting speed in lathe operations.

Affective Domain:

Appreciate the importance of selecting the correct cutting tool for different operations.
Value the importance of safety precautions when working with lathe machines and tools.

Psychomotor Domain:

Identify various lathe cutting tools from a collection.
Calculate cutting speed for a given lathe operation using the correct formula.
Select the appropriate tool holder for different cutting tools.

Work cooperatively in groups to identify and discuss different cutting tools.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Schools Education Curriculum
State Unified Scheme of Work
D.N. Denyer, A.J. Tredgold & H. Williams. (2010). Metalwork Technology for Senior Secondary Schools. Macmillan Publishers.
https://www.machining-design.com/lathe-cutting-tools/
https://www.engineersedge.com/machining_tables/lathe_cutting_speed_feed_table.htm

Instructional Materials

The teacher will teach this lesson with the aid of:

Assorted lathe cutting tools (e.g., right hand tool, left hand tool, parting tool, boring tool)
Charts showing different lathe cutting tools and their parts
A calculator
Whiteboard and markers

Rationale for the Lesson

This lesson helps pupils understand the essential tools used in lathe operations and how to determine the correct cutting speed. This knowledge is important for performing precise and efficient metal turning, contributing to their practical skills in metalwork and preparing them for further vocational training.

Prerequisite/Previous Knowledge

Pupils have basic knowledge of the lathe machine and its main parts, as well as general workshop safety rules.

Lesson Content/Board Summary

Lathe Cutting Tools

Introduction to Lathe Cutting Tools

Lathe cutting tools are specialized tools used in a lathe machine to remove material from a workpiece, shaping it into the desired form. These tools are typically made from hard, wear-resistant materials like high-speed steel (HSS), carbide, or ceramic.

Types of Lathe Cutting Tools

The type of cutting tool used depends on the operation to be performed and the material being machined. The following are common types:

Right Hand Tool: Used for turning operations where the cut progresses from right to left. The cutting edge is on the left side of the tool point.
Left Hand Tool: Used for turning operations where the cut progresses from left to right. The cutting edge is on the right side of the tool point.
Slotting Tool (Parting-off Tool): Used to cut grooves or to completely cut off a section of the workpiece. It has a narrow cutting edge.
Facing Tool: Used to machine the end face of a workpiece, making it flat and perpendicular to the axis of rotation.
Boring Tool: Used to enlarge an existing hole or to machine an internal cylindrical surface.
Threading Tool: Used to cut external or internal threads on a workpiece.
Knurling Tool: Used to produce a textured pattern on the surface of a workpiece, usually for grip.

Tool Holders

Tool holders are devices used to securely clamp and position the cutting tool in the lathe’s tool post. They ensure the tool is held rigidly and at the correct height relative to the workpiece, which is critical for accurate and safe machining.

Cutting Speed for Lathe Operations

Cutting speed (CS) is the rate at which the cutting edge of the tool passes over the surface of the workpiece. It is typically expressed in meters per minute (m/min) or feet per minute (ft/min).

Formula for Cutting Speed:
CS = (πDN) / 1000

Where:

CS = Cutting Speed (m/min)
π (Pi) = Approximately 3.142 or 22/7
D = Diameter of the workpiece (mm)
N = Revolutions per minute (RPM) of the workpiece
1000 = Conversion factor (to convert mm to meters)

Factors Affecting Cutting Speed:

Type of workpiece material (e.g., steel, aluminum, brass).
Type of cutting tool material (e.g., HSS, carbide).
Depth of cut.
Feed rate (how fast the tool moves along the workpiece).
Required surface finish.
Rigidity of the machine and workpiece.
Use of cutting fluids (coolants).

Worked Examples for Cutting Speed Calculation:

Example 1:
A mild steel workpiece with a diameter of 50 mm is machined at 400 RPM. Calculate the cutting speed.

Step 1: Write down the formula.
CS = (πDN) / 1000

Step 2: Substitute the given values.
D = 50 mm, N = 400 RPM, π ≈ 3.142
CS = (3.142 × 50 × 400) / 1000

Step 3: Calculate the product.
CS = (62840) / 1000

Step 4: Perform the division and state the unit.
CS = 62.84 m/min

Therefore, the cutting speed is 62.84 meters per minute.

Example 2:
A brass workpiece with a diameter of 30 mm needs to be machined at a cutting speed of 90 m/min. Calculate the required spindle speed (RPM).

Step 1: Write down the formula and rearrange to find N.
CS = (πDN) / 1000
N = (CS × 1000) / (πD)

Step 2: Substitute the given values.
CS = 90 m/min, D = 30 mm, π ≈ 3.142
N = (90 × 1000) / (3.142 × 30)

Step 3: Calculate the numerator and denominator.
N = 90000 / 94.26

Step 4: Perform the division and state the unit.
N ≈ 954.8 RPM

Therefore, the required spindle speed is approximately 955 revolutions per minute.

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 reviews the previous lesson on the parts of a lathe machine. The teacher then introduces the topic by asking pupils what tools they think are used to shape metal on a lathe.
Pupils’ Activity: Pupils respond to the teacher’s questions and share their ideas about lathe tools.
Learning Point: Pupils recall previous knowledge and are prepared for the new topic.

Step 2: Explanation of Lathe Cutting Tools

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher defines lathe cutting tools and explains their general purpose using charts and actual tools. The teacher emphasizes the importance of tool material.
Pupils’ Activity: Pupils listen attentively, observe the tools, and ask questions for clarification.
Learning Point: Pupils understand the definition and purpose of lathe cutting tools.

Step 3: Types of Lathe Cutting Tools

Time: 8 minutes
Teaching Skill: Illustration/Identification
Teacher’s Activity: The teacher displays various types of lathe cutting tools (right hand, left hand, slotting, etc.) and explains the specific function of each. The teacher encourages pupils to identify the tools.
Pupils’ Activity: Pupils identify the different tools and relate them to their functions. They may handle the tools carefully.
Learning Point: Pupils can identify and differentiate between various lathe cutting tools and state their uses.

Step 4: Tool Holders

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains the function of tool holders and their importance in securely clamping the cutting tool in the lathe’s tool post. The teacher may show a tool holder.
Pupils’ Activity: Pupils listen and understand the role of tool holders in lathe operations.
Learning Point: Pupils understand the purpose and importance of tool holders.

Step 5: Introduction to Cutting Speed

Time: 5 minutes
Teaching Skill: Definition/Concept Introduction
Teacher’s Activity: The teacher defines cutting speed and explains why it is an important parameter in machining. The teacher introduces the formula for calculating cutting speed.
Pupils’ Activity: Pupils listen and copy the definition and the formula into their notes.
Learning Point: Pupils understand the concept of cutting speed and its formula.

Step 6: Calculation of Cutting Speed

Time: 8 minutes
Teaching Skill: Problem Solving/Demonstration
Teacher’s Activity: The teacher explains each variable in the cutting speed formula and solves two worked examples on the board, demonstrating step-by-step calculations. The teacher also discusses factors affecting cutting speed.
Pupils’ Activity: Pupils follow the calculations, copy the examples, and ask questions where they need clarification. They may attempt to solve similar problems.
Learning Point: Pupils can calculate cutting speed and explain factors influencing it.

Step 7: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define a lathe cutting tool.
Mention three types of lathe cutting tools.
State the purpose of a tool holder.
Write down the formula for calculating cutting speed and explain each variable.
A workpiece with a diameter of 40 mm is machined at 500 RPM. Calculate the cutting speed.

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, reiterating the importance of knowing different cutting tools and calculating cutting speed for effective lathe operations. The teacher gives homework.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils consolidate their learning and are assigned further practice.

Lesson Keywords

Lathe – A machine tool used for shaping metal or wood by rotating the workpiece against a cutting tool.
Cutting Tool – An implement used to remove material from a workpiece.
Right Hand Tool – A lathe tool used for turning from right to left, with the cutting edge on the left.
Left Hand Tool – A lathe tool used for turning from left to right, with the cutting edge on the right.
Slotting Tool – A narrow tool used for cutting grooves or parting off material.
Tool Holder – A device that clamps and positions a cutting tool in the tool post.
Cutting Speed (CS) – The rate at which the cutting edge passes over the workpiece surface.
Revolutions Per Minute (RPM) – The number of rotations a spindle or workpiece makes in one minute.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide additional challenges, such as asking them to calculate RPM given cutting speed and diameter, or to identify specific tool angles. For pupils who need more support, the teacher can provide simplified diagrams, re-explain concepts individually, and offer more guided practice on cutting speed calculations.

Note for teachers using this lesson plan

Ensure a variety of actual lathe cutting tools are available for pupils to observe and handle carefully. Emphasize safety precautions when discussing tools and lathe operations. Encourage active participation during the calculation examples to build confidence in problem-solving.