Lesson Note on Computer Aided Drawing: Auxiliary Elevations and Plans for SS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: Second Term
Week: 7
Age: 16 years
Duration: 45 minutes
Subject: Technical Drawing
Curriculum Theme: Technical Drawing
Previous Lesson: Computer Aided Drawing: Isometric, Oblique and Perspective Views.
Topic: COMPUTER AIDED DRAWING
Subject Matter: Computer drawing of auxiliary elevations and plans (first auxiliary, second auxiliary, truncated geometrical solids)

Specific Objectives

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

Cognitive Domain:

• Define Computer Aided Drawing (CAD).
• Explain the purpose of auxiliary elevations and plans.
• Identify the types of auxiliary views.

Affective Domain:

• Appreciate the precision and efficiency of CAD in technical drawing.
• Develop interest in using CAD software for various drawing tasks.

Psychomotor Domain:

• Operate CAD software to create basic drawings.
• Draw a first auxiliary elevation and plan using CAD.
• Draw a second auxiliary elevation and plan using CAD.
• Draw a truncated geometrical solid using CAD.

Social Domain:

• Collaborate with peers when encountering challenges in CAD software.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• Oluyemi, A. O. (2010). Technical Drawing for Senior Secondary Schools. Evans Brothers (Nigeria Publishers) Limited.

Instructional Materials

The teacher will teach this lesson with the aid of:

• Computers with CAD software installed (e.g., CorelDraw, Harvard Graphics, AutoCAD).
• Projector or interactive whiteboard for demonstration.
• Prepared examples of auxiliary views and truncated solids.

Rationale for the Lesson

This lesson helps pupils understand and apply modern drawing techniques using computers, which is important for accuracy and efficiency in technical drawing. It prepares them for advanced studies and careers in engineering, architecture, and other related fields where computer-aided design is standard practice.

Prerequisite/Previous Knowledge

Pupils are expected to have basic knowledge of manual drawing of orthogonal projections, including elevations and plans, and some familiarity with basic computer operations.

Lesson Content/Board Summary

COMPUTER AIDED DRAWING (CAD)

Introduction to CAD

Computer Aided Drawing (CAD) is the use of computer systems to assist in the creation, modification, analysis, or optimization of a design. CAD software helps designers and engineers to create precise 2D and 3D drawings and models.

The following are advantages of CAD over manual drawing:

• Increased precision and accuracy.
• Faster drawing and modification.
• Easy storage and retrieval of designs.
• Ability to create complex designs easily.
• Reduced errors and improved consistency.

Auxiliary Views in CAD

An auxiliary view is an orthographic projection of an object onto a plane that is not parallel to any of the principal projection planes (frontal, horizontal, or profile). Auxiliary views are used to show the true size and shape of inclined or oblique surfaces that appear distorted in standard orthographic views.

Types of Auxiliary Views:

• First Auxiliary View: Projected from a primary orthographic view (e.g., front view) to show the true shape of a surface inclined to that primary view.
• Second Auxiliary View: Projected from a first auxiliary view to show the true shape of a surface that is oblique to all principal planes.

Example: Drawing a First Auxiliary Elevation in CAD

To draw a first auxiliary elevation of an inclined surface using CAD software:

1. Step 1: Draw the Principal Views. Start by drawing the front view and top view (plan) of the object using the appropriate drawing tools in the CAD software. Ensure all lines are accurate and dimensions are correct.
2. Step 2: Identify the Inclined Surface. Locate the inclined surface whose true shape needs to be shown.
3. Step 3: Draw the Reference Line. Draw a line parallel to the inclined surface in the primary view (e.g., front view). This line represents the fold line between the primary view and the auxiliary view.
4. Step 4: Project Perpendicular Lines. From each critical point on the inclined surface in the primary view, draw projection lines perpendicular to the reference line.
5. Step 5: Transfer Distances. Measure the perpendicular distances of the points from the fold line in the adjacent view (e.g., top view). Transfer these distances along the projection lines from the reference line in the auxiliary view direction.
6. Step 6: Connect the Points. Connect the transferred points to form the true shape of the inclined surface. Add any hidden lines or centerlines as necessary.

Drawing Truncated Geometrical Solids in CAD

A truncated geometrical solid is a solid that has been cut by a plane, resulting in a new, non-standard face. Examples include truncated pyramids, cones, and prisms.

Example: Drawing a Truncated Pyramid in CAD

To draw a truncated pyramid using CAD software:

1. Step 1: Draw the Base and Height. Begin by drawing the base of the pyramid (e.g., a square for a square pyramid) in the top view and the corresponding front view showing the pyramid’s height and apex.
2. Step 2: Define the Cutting Plane. Draw the cutting plane line in the front view, indicating where the pyramid is truncated. This line will usually be inclined.
3. Step 3: Locate Intersection Points. Determine the points where the cutting plane intersects the edges of the pyramid in the front view.
4. Step 4: Project Intersection Points to Plan. Project these intersection points from the front view down to the corresponding edges in the top view (plan).
5. Step 5: Connect Points in Plan. Connect the projected points in the top view to show the shape of the cut surface on the plan.
6. Step 6: Draw the True Shape of the Cut Surface (if required). If the true shape of the cut surface is needed, draw an auxiliary view by projecting perpendicular to the cutting plane line and transferring distances, similar to drawing an auxiliary elevation.
7. Step 7: Complete the Drawing. Use appropriate line types to show the visible and hidden edges of the truncated solid in both views.

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 reminds them of their previous knowledge in manual drawing of orthogonal projections. The teacher then introduces the topic by asking pupils if they have ever wondered how modern designs are created with such precision.
Pupils’ Activity: Pupils respond to the teacher’s greetings and questions, relating their prior knowledge to the new topic.
Learning Point: Pupils recall previous knowledge and are prepared for the new lesson.

Step 2: Explanation of CAD

Time: 7 minutes
Teaching Skill: Explanation/Lecture
Teacher’s Activity: The teacher defines Computer Aided Drawing (CAD) and explains its importance and advantages over traditional manual drawing methods, using the projector to show examples of CAD drawings.
Pupils’ Activity: Pupils listen attentively, ask questions for clarification, and take notes on the definition and advantages of CAD.
Learning Point: Pupils understand what CAD is and its benefits.

Step 3: Introduction to Auxiliary Views

Time: 7 minutes
Teaching Skill: Explanation/Visual Aid
Teacher’s Activity: The teacher explains what auxiliary views are, why they are necessary in technical drawing, and introduces the two main types: first auxiliary and second auxiliary views. The teacher uses diagrams to illustrate these concepts.
Pupils’ Activity: Pupils observe the diagrams, listen to the explanation, and ask questions about the different types and purposes of auxiliary views.
Learning Point: Pupils understand the concept and types of auxiliary views.

Step 4: Demonstration of First Auxiliary View

Time: 8 minutes
Teaching Skill: Demonstration/Practical
Teacher’s Activity: The teacher demonstrates how to draw a first auxiliary elevation of an inclined surface using CAD software on a computer, projected for all pupils to see. The teacher guides them through each step.
Pupils’ Activity: Pupils observe the teacher’s demonstration carefully, noting the tools and steps used in the CAD software.
Learning Point: Pupils learn the practical steps for creating a first auxiliary view using CAD.

Step 5: Demonstration of Second Auxiliary View & Truncated Solids

Time: 8 minutes
Teaching Skill: Demonstration/Practical
Teacher’s Activity: The teacher further demonstrates how to draw a second auxiliary view and then how to represent truncated geometrical solids (e.g., a truncated pyramid) using the CAD software, emphasizing the projection and intersection techniques.
Pupils’ Activity: Pupils pay close attention to the advanced demonstrations, identifying similarities and differences in the drawing processes.
Learning Point: Pupils understand how to draw more complex auxiliary views and truncated solids with CAD.

Step 6: Pupils’ Practical Session

Time: 5 minutes
Teaching Skill: Guided Practice
Teacher’s Activity: The teacher guides pupils as they attempt to replicate the demonstrated drawings on their individual computers or in pairs, providing assistance and feedback.
Pupils’ Activity: Pupils actively engage in drawing auxiliary views and truncated solids using the CAD software, seeking help when needed.
Learning Point: Pupils gain hands-on experience and reinforce their learning through practice.

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 Computer Aided Drawing (CAD)?
2. State two advantages of using CAD over manual drawing.
3. Define an auxiliary view.
4. Mention the two main types of auxiliary views.
5. Briefly describe one step in drawing a first auxiliary elevation using CAD.

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 learning points about CAD, auxiliary views, and truncated solids, reminding pupils of the importance of practice. The teacher assigns homework to draw a specified object with an auxiliary view using CAD.
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils consolidate their learning and are given tasks for further practice.

Lesson Keywords

• CAD – Computer Aided Drawing, using computer systems for design.
• Auxiliary View – An orthographic projection onto a plane not parallel to principal planes.
• Elevation – A view of an object from the front, back, or side.
• Plan – A view of an object from above (top view).
• Truncated Solid – A solid cut by a plane, resulting in a new face.

Differentiation

For struggling learners, the teacher will provide simplified examples and one-on-one assistance during the practical session. Advanced learners will be challenged to explore more complex features of the CAD software, such as dimensioning or creating 3D models from their 2D drawings.

Note for teachers using this lesson plan

Ensure that all computers are functional and have the necessary CAD software installed before the lesson. Familiarize yourself with the specific software being used to effectively demonstrate and assist pupils. If computers are limited, organize pupils into small groups for collaborative learning and practical sessions. Emphasize safety precautions when using computer equipment.