Sections and Sectional Views, Revolved and Offset Sections for SS 3

Class: SS 3
Term: First Term
Week: 9
Age: 17 years
Duration: 60 minutes
Subject: Technical Drawing
Curriculum Theme: Orthographic Projection and Sectional Views
Previous Lesson: Engineering Working Drawings of Bearing Brackets and Pulleys
Topic: SECTIONS AND SECTIONAL VIEWS
Subject Matter: Type of section revolving section off centre etc

Specific Objectives

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

Cognitive Domain

• Define what a section and a sectional view are.
• Identify the purpose of using sectional views in technical drawing.
• Differentiate between various types of sections, specifically revolving and offset sections.
• Explain the application of revolved and offset sections in drawing machine parts.

Affective Domain

• Appreciate the importance of sectional views for clarity in technical drawings.
• Show keen interest in accurately interpreting and drawing sectional views.
• Collaborate effectively with peers during drawing activities.

Psychomotor Domain

• Sketch simple examples of revolved sections.
• Draw accurate offset sections of given machine parts.
• Construct sectional views of machine assemblies using appropriate techniques.

Social Domain

• Discuss the advantages of using sectional views in engineering communication.
• Share drawing techniques and solutions with classmates.

Reference Materials

The following resources were used in planning this lesson:

• 2014 Senior Secondary Education Curriculum (SSEC)
• Relevant State Unified Scheme of Work
• A suitable Technical Drawing textbook for SS 3
• FCT ERC/NAPPS Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Diagrams of machine parts with sectional views
• Figures illustrating revolved and offset sections
• Charts showing different types of sections
• Drawing boards, T-squares, set squares, pencils, erasers, and drawing paper
• Actual machine parts (if available) to demonstrate internal features

Rationale for the Lesson

This lesson is important as it equips students with the fundamental skills to understand and represent the internal features of objects, which are often hidden in standard orthographic projections. Mastering sectional views enhances their ability to communicate design intent clearly and accurately in engineering and manufacturing contexts. This knowledge is crucial for further studies in engineering and related technical fields.

Prerequisite/Previous Knowledge

Students should have a basic understanding of orthographic projection, including first and third angle projection, and the ability to draw basic views of simple objects.

Lesson Content/Board Summary

SECTIONS AND SECTIONAL VIEWS

Meaning of Section and Sectional View

In technical drawing, a section refers to the imaginary cut made through an object to reveal its internal structure. A sectional view is the orthographic projection of an object as it would appear after being cut by an imaginary cutting plane.

The main purpose of sectional views is to clarify the internal construction of an object that cannot be clearly shown by hidden lines in standard exterior views. Section lines (hatching) are used to indicate the solid material that has been cut by the imaginary cutting plane.

Types of Sections

While there are several types of sections, this lesson focuses on those that clarify specific internal features or complex geometries.

1. Full Section: The cutting plane passes entirely through the object, removing half of it.
2. Half Section: The cutting plane passes through one-quarter of the object, revealing both internal and external features in a single view.
3. Revolved Section: This type of section is used to show the cross-sectional shape of a rib, spoke, arm, or similar elongated feature directly on the view where the feature appears. The cutting plane is passed perpendicular to the axis of the feature, and the resulting section is then revolved 90 degrees into the plane of the drawing.

Application of Revolved Sections

Revolved sections are typically used for:

1. Showing the true shape of a cross-section of a bar, spoke, or arm.
2. Avoiding the need for a separate view, thus saving space and improving clarity.

Drawing Revolved Sections

Revolved sections can be drawn in two main ways:

1. Superimposed: The section is drawn directly on the view, often breaking the outline of the object. The outline of the revolved section is drawn with a continuous thick line, and the sectioned area is hatched.
2. Broken-out: The section is drawn within a break in the object’s outline, usually bounded by a thin, irregular line.

4. Offset Section: An offset section is used when the internal features to be shown do not lie in a straight line. The cutting plane is “bent” or offset to pass through various features that are not in the same plane. The bends in the cutting plane are not shown in the sectional view; the view is drawn as if the cutting plane were straight.

Application of Offset Sections

Offset sections are particularly useful for:

1. Revealing multiple internal features that are not aligned.
2. Simplifying complex internal geometries into a single, comprehensive sectional view.

Drawing Offset Sections

When drawing an offset section:

1. The cutting plane line indicates the path of the imaginary cut, showing the offsets.
2. In the sectional view, the changes in direction of the cutting plane are ignored, and the view is drawn as if the entire cutting plane were in one plane.
3. No lines are drawn at the points where the cutting plane changes direction in the sectional view, as these are imaginary bends.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Observation, Practical Activity

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Explaining/Questioning

Teacher’s Activity: The teacher introduces the lesson by asking students about the limitations of showing internal details with hidden lines in orthographic projections. The teacher then explains that sectional views overcome this limitation by showing internal features clearly.

Pupils’ Activity: Pupils respond to questions and listen attentively to the introduction.

Learning Point: Limitations of hidden lines

Step 2: Definition of Section and Sectional View

Time: 10 minutes

Teaching Skill: Explanation/Illustration

Teacher’s Activity: The teacher defines what a section and a sectional view are, using diagrams and simple objects to illustrate the concept of an imaginary cutting plane. The teacher also explains the purpose of using sectional views.

Pupils’ Activity: Pupils observe the illustrations, ask questions for clarification, and understand the basic concepts.

Learning Point: Meaning of sectioning

Step 3: Introduction to Types of Sections

Time: 5 minutes

Teaching Skill: Categorisation/Briefing

Teacher’s Activity: The teacher briefly mentions common types of sections like full and half sections to provide context, then states that the lesson will focus on revolved and offset sections.

Pupils’ Activity: Pupils listen and recall previous knowledge about basic sections.

Learning Point: Overview of section types

Step 4: Explaining Revolved Sections

Time: 10 minutes

Teaching Skill: Demonstration/Explanation

Teacher’s Activity: The teacher explains revolved sections, demonstrating with diagrams how a cutting plane passes through a feature like a spoke or rib and how the section is then rotated into the view. The teacher shows examples of superimposed and broken-out revolved sections.

Pupils’ Activity: Pupils observe the diagrams and explanations, asking questions about the rotation and placement of the section.

Learning Point: Revolved section principles

Step 5: Explaining Offset Sections

Time: 10 minutes

Teaching Skill: Demonstration/Explanation

Teacher’s Activity: The teacher explains offset sections, using diagrams to show how the cutting plane is bent to pass through multiple non-aligned internal features. The teacher clarifies that the bends are not shown in the resulting sectional view.

Pupils’ Activity: Pupils study the diagrams, understand the concept of a bent cutting plane, and note how the sectional view is drawn.

Learning Point: Offset section principles

Step 6: Guided Drawing Practice

Time: 10 minutes

Teaching Skill: Guided Practice/Supervision

Teacher’s Activity: The teacher provides simple drawing exercises for revolved and offset sections. The teacher guides students to draw a simple machine part requiring a revolved section and another requiring an offset section, offering individual assistance.

Pupils’ Activity: Pupils attempt to draw the sectional views on their drawing paper, applying the concepts learned, and seeking help when needed.

Learning Point: Drawing sectional views

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 the primary purpose of a sectional view?
2. Explain the difference between a revolved section and an offset section.
3. When would you use a revolved section in a technical drawing?
4. Describe how an offset cutting plane is represented in the sectional view.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding section types

Step 8: Note-Taking

Time: 10 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on sections, sectional views, revolved sections, and offset sections into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Recording key concepts

Step 9: Conclusion

Time: 5 minutes

Teaching Skill: Summarising/Reinforcement

Teacher’s Activity: The teacher briefly summarises the importance of sectional views, especially revolved and offset sections, for clear communication in technical drawing. The teacher encourages students to practice drawing these sections regularly.

Pupils’ Activity: Pupils listen to the summary and prepare for the next lesson.

Learning Point: Reinforcing lesson importance

Continuous Assessment/Further Study

Type: Homework/Practice Exercise

Instruction: Draw the orthographic views (Front View and Top View) of the given machine part. Then, create a full sectional front view, a revolved section of the central rib, and an offset section to show the internal holes. Ensure all section lines and drawing conventions are correctly applied.

1. Draw a machine bracket with a central rib and two non-aligned internal holes.
2. Produce the necessary orthographic views.
3. Apply a revolved section to clearly show the cross-section of the rib.
4. Apply an offset section to reveal the two internal holes.

Lesson Keywords

• Section – An imaginary cut through an object.
• Sectional View – An orthographic projection showing the internal features of an object after an imaginary cut.
• Cutting Plane – An imaginary plane that cuts through an object to create a section.
• Section Lines (Hatching) – Parallel lines used to indicate the solid material cut by the cutting plane.
• Revolved Section – A section rotated 90 degrees into the plane of the drawing to show the cross-sectional shape of a feature.
• Offset Section – A section created by a bent or stepped cutting plane to show multiple non-aligned internal features.

Differentiation

For struggling learners: Provide simpler diagrams with fewer features for drawing practice. Offer pre-drawn outlines for them to complete the sectioning. Focus on identifying the cutting plane path for offset sections.

For advanced learners: Challenge them with more complex machine parts requiring multiple types of sections in a single drawing. Encourage them to design a simple part and then draw its sectional views, justifying their choice of section type.

Suggested Lesson Videos

For further understanding and visual demonstration, students can search on YouTube for:

• technical drawing revolved section tutorial ss3
• technical drawing offset section tutorial ss3
• types of sectional views technical drawing