Lesson Note on Milling Machine and Dividing Head for SS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 3rd Term
Week: 10
Age: 16 years
Duration: 45 minutes
Subject: Metal Work
Curriculum Theme: Pre-Vocational Studies
Previous Lesson: Shaping and Milling Machines.
Topic: Milling Machine
Subject Matter: Meaning of milling machine (machine for cutting metals using rotating cutter), classification of milling machines, basic milling operations, milling cutter, direction of rotation and feed, universal dividing head (gear cutting), indexing calculation.

Specific Objectives

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

Cognitive Domain:

• Define a milling machine.
• State the different classifications of milling machines.
• List basic milling operations.
• Describe the types of milling cutters.
• Explain the direction of rotation and feed in milling.
• Explain the purpose of a universal dividing head.
• State the formula for simple indexing calculation.

Affective Domain:

• Appreciate the importance of milling machines in metal fabrication.
• Develop interest in the safe operation of milling machines.
• Value the precision achieved through milling operations.

Psychomotor Domain:

• Identify the main parts of a milling machine and a dividing head.
• Perform simple indexing calculations.
• Draw a basic diagram illustrating conventional and climb milling.

Social Domain:

• Collaborate with peers to discuss different milling applications.
• Share ideas on how to solve indexing problems.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• Metal Work for Senior Secondary Schools by E.J. Love and J.W. Love

Instructional Materials

The teacher will teach this lesson with the aid of:

• A milling machine (actual or diagram)
• A dividing head (actual or diagram)
• Various milling cutters
• Charts showing milling operations and calculations

Rationale for the Lesson

Understanding milling machines is important because they are widely used in manufacturing for precise metal shaping. This lesson helps pupils grasp how these machines work and how to perform calculations for specific tasks like gear cutting, preparing them for practical applications in engineering and metalwork.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of machine tools, metal properties, and fundamental workshop safety rules.

Lesson Content/Board Summary

Milling Machine

Meaning of Milling Machine

A milling machine is a machine tool used for machining solid materials. It performs a machining process called milling, which uses rotary cutters to remove material from a workpiece by advancing the cutter into the workpiece. It can machine flat surfaces, angular surfaces, slots, grooves, and produce gears.

Classification of Milling Machines

Milling machines can be classified based on their construction and operation:

• Column and Knee Type Milling Machines:
  • Horizontal Milling Machine
  • Vertical Milling Machine
  • Universal Milling Machine
• Production Type Milling Machines:
  • Planer Type Milling Machine
  • Tracer Controlled Milling Machine
  • Numerical Control (NC) and Computer Numerical Control (CNC) Milling Machine

Basic Milling Operations

Some common milling operations include:

• Plain or Slab Milling: Machining a flat surface parallel to the axis of the cutter.
• Face Milling: Machining a flat surface perpendicular to the axis of the cutter.
• End Milling: Cutting slots, grooves, and pockets using an end mill.
• Side Milling: Machining vertical flat surfaces on the side of a workpiece.
• Slotting: Creating slots or keyways.
• Gear Cutting: Producing teeth on gear blanks.
• Drilling and Boring: Creating holes.

Milling Cutter

A milling cutter is a rotary cutting tool used in milling machines. It has multiple cutting edges (teeth) that remove material from the workpiece.

Types of milling cutters include:

• Plain milling cutters
• Side milling cutters
• Face milling cutters
• End mills
• Slab mills
• Angle milling cutters
• Form cutters (e.g., gear cutters)

Direction of Rotation and Feed

There are two main methods of feeding the workpiece relative to the cutter’s rotation:

• Conventional (Up) Milling: The workpiece is fed against the rotation of the cutter. The chip thickness starts at zero and increases. This method lifts the workpiece, requiring strong clamping.
• Climb (Down) Milling: The workpiece is fed in the same direction as the rotation of the cutter. The chip thickness starts at maximum and decreases. This method pulls the workpiece into the cutter, often preferred for stability and better surface finish.

Universal Dividing Head (Gear Cutting)

The universal dividing head is an accessory used on milling machines to divide the circumference of a workpiece into equally spaced divisions. It is essential for operations like gear cutting, milling splines, fluting reamers, and milling polygons. It consists of a worm and worm wheel mechanism, typically with a 40:1 ratio (40 turns of the crank for 1 revolution of the workpiece).

Indexing Calculation

Indexing is the process of rotating the workpiece to a precise angle or number of divisions. Simple indexing uses the following formula:

Formula:

N = 40 / T

Where:

• N = Number of turns of the indexing crank
• 40 = Worm wheel ratio (standard for most dividing heads)
• T = Number of divisions (teeth) required on the workpiece

Worked Examples:

Example 1: Calculate the number of turns of the indexing crank required to cut a gear with 20 teeth.

Step 1: Write down the formula.

N = 40 / T

Step 2: Substitute the given values.

T = 20 teeth

N = 40 / 20

Step 3: Calculate the result.

N = 2 turns

Therefore, the indexing crank must be turned 2 full revolutions for each tooth.

Example 2: Determine the indexing for cutting a gear with 40 teeth.

Step 1: Write down the formula.

N = 40 / T

Step 2: Substitute the given values.

T = 40 teeth

N = 40 / 40

Step 3: Calculate the result.

N = 1 turn

Therefore, the indexing crank must be turned 1 full revolution for each tooth.

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 reviews the previous lesson on basic machine tools and asks pupils to mention some common machining processes. The teacher then introduces the topic “Milling Machine” by showing a picture or diagram of a milling machine.
Pupils’ Activity: Pupils respond to questions about previous knowledge and observe the provided visual aid.
Learning Point: Pupils recall prior knowledge and are introduced to the new topic.

Step 2: Meaning and Classification of Milling Machine

Time: 8 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines a milling machine as a machine tool that uses rotary cutters to remove material. The teacher then explains and lists the different classifications of milling machines, such as column and knee type and production type.
Pupils’ Activity: Pupils listen attentively, take notes, and ask questions for clarification.
Learning Point: Pupils understand the definition and classifications of milling machines.

Step 3: Basic Milling Operations and Milling Cutters

Time: 8 minutes
Teaching Skill: Explanation/Listing
Teacher’s Activity: The teacher explains various basic milling operations like plain milling, face milling, and slotting, using diagrams if available. The teacher then describes what a milling cutter is and lists different types of cutters, showing examples where possible.
Pupils’ Activity: Pupils listen, observe the diagrams/examples, and note the different operations and cutter types.
Learning Point: Pupils learn about common milling operations and the tools used.

Step 4: Direction of Rotation and Feed

Time: 7 minutes
Teaching Skill: Explanation/Comparison
Teacher’s Activity: The teacher explains the two main methods of feeding the workpiece: conventional (up) milling and climb (down) milling. The teacher highlights the differences and advantages/disadvantages of each method.
Pupils’ Activity: Pupils pay attention, compare the two methods, and understand their implications.
Learning Point: Pupils understand the concepts of conventional and climb milling.

Step 5: Universal Dividing Head

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the purpose of the universal dividing head as an accessory for dividing the circumference of a workpiece. The teacher describes its key components and its role in gear cutting.
Pupils’ Activity: Pupils listen, observe the dividing head (actual or diagram), and understand its function.
Learning Point: Pupils understand the function and importance of the universal dividing head.

Step 6: Indexing Calculation

Time: 8 minutes
Teaching Skill: Problem Solving/Demonstration
Teacher’s Activity: The teacher introduces the concept of indexing and explains the simple indexing formula (N = 40/T). The teacher demonstrates how to apply the formula by solving two worked examples on the board, showing step-by-step calculations.
Pupils’ Activity: Pupils copy the formula and worked examples, and attempt to solve similar problems given by the teacher.
Learning Point: Pupils learn how to perform simple indexing calculations for gear cutting.

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 a milling machine?
2. List two classifications of milling machines.
3. Mention three basic milling operations.
4. State the formula for simple indexing.
5. Calculate the number of turns of the indexing crank required to cut a gear with 10 teeth.

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 milling machines and indexing. The teacher then assigns homework, asking pupils to research compound indexing.
Pupils’ Activity: Pupils listen to the summary and note down the homework assignment.
Learning Point: Pupils consolidate their understanding and receive further learning tasks.

Lesson Keywords

• Milling Machine – A machine tool that uses rotating cutters to remove material from a workpiece.
• Milling Cutter – A multi-edged rotary tool used for machining in a milling machine.
• Conventional Milling – Workpiece fed against the rotation of the cutter.
• Climb Milling – Workpiece fed in the same direction as the rotation of the cutter.
• Dividing Head – An accessory used to divide the circumference of a workpiece into equal divisions.
• Indexing – The process of rotating a workpiece to a precise angle or number of divisions.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide additional complex indexing problems or ask them to research the different types of indexing (e.g., compound, differential). For pupils needing more support, the teacher can provide simplified diagrams of milling operations and offer one-on-one guidance during indexing calculations.

Note for teachers using this lesson plan

Ensure that safety precautions are emphasized throughout the lesson, especially when discussing machine operation. If an actual milling machine is available, a brief practical demonstration of its parts and basic movements would greatly enhance understanding. Encourage pupils to ask questions and participate actively.