Drawing Practices – Oblique Drawing

Subject: Basic Technology

Class: JSS 3

Term: First Term

Week: 10

Age: 12–15 years

Topic: Drawing Practices – Oblique Drawing

Sub-topic: Definition, Types, and Construction of Simple Objects

Duration: 60 minutes

Behavioural Objectives

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

1. Define oblique drawing.
2. Identify and explain the types of oblique drawing.
3. Construct simple objects using oblique projection.
4. Distinguish between oblique and isometric drawings.

Keywords

• Oblique Drawing
• Pictorial Projection
• Cavalier Projection
• Cabinet Projection
• Depth Axis
• 45-degree Angle

Set Induction

The teacher shows an oblique drawing of a simple object, such as a table or a box, and asks students how it differs from a regular 2D sketch. The discussion introduces the concept of depth representation using oblique drawing.

Entry Behaviour

Students already have experience with isometric drawings and orthographic projections.

Learning Resources and Materials

• Oblique graph paper
• Models of simple objects (e.g., rectangular blocks)
• Rulers, pencils, erasers
• Whiteboard for demonstration

Building Background/Connection to Prior Knowledge

In the previous lesson, students learned about isometric drawings, which also represent objects in 3D. Now, they will explore oblique drawing, which shows an object with the front view in full scale and the depth view at an angle (usually 45 degrees).

Embedded Core Skills

• Visual thinking and spatial reasoning
• Fine motor skills
• Problem-solving

Learning Materials

• Oblique graph sheets
• Diagrams of oblique and isometric drawings
• Models of 3D objects

Reference Books

• Lagos State Scheme of Work
• Basic Technology Textbook for Junior Secondary Schools
• “Engineering Drawing” by R.K. Dhawan

Instructional Materials

• Drawing tools (rulers, compasses, pencils)
• Oblique graph paper
• 3D models (e.g., small blocks)

Content

I. Definition of Oblique Drawing

• Oblique drawing is a type of pictorial projection in which the front face of the object is drawn in full scale, while the other sides are projected at an angle, typically 45 degrees, to show depth.
• It is used to represent objects simply without distorting the front view, making it suitable for objects with circular or curved features.

II. Types of Oblique Drawing

1. Cavalier Projection:
   • The depth is drawn at full scale, meaning no reduction in size.
   • Objects appear slightly stretched in the depth axis.
2. Cabinet Projection:
   • The depth is reduced to half scale to make the object look more natural.
   • This type of oblique drawing is commonly used in furniture design and product illustrations.

III. Construction of Simple Objects in Oblique Drawing

Steps to Draw a Simple Box Using Oblique Projection

1. Step 1: Draw the front face (e.g., a square) in full scale.
2. Step 2: From the corners of the front face, draw depth lines at 45 degrees to the horizontal.
3. Step 3: Decide whether the depth lines should be full length (Cavalier) or half length (Cabinet).
4. Step 4: Complete the depth faces by connecting the corresponding points.
5. Step 5: Darken the lines to finalize the drawing.

Examples of Simple Objects to Draw in Oblique Projection

1. Box
2. Table
3. Chair
4. Cuboid
5. Circular Pipe

Evaluation (Fill-in-the-Blank Questions)

1. __________ drawing shows an object with its front face in full scale.
   (a) Oblique (b) Orthographic (c) Isometric (d) Cavalier
2. In __________ projection, the depth is drawn at full scale.
   (a) Cabinet (b) Cavalier (c) Isometric (d) Orthographic
3. Cabinet projection shows the depth at __________ scale.
   (a) half (b) full (c) double (d) three-quarter
4. The depth lines in oblique drawing are drawn at __________ degrees.
   (a) 30 (b) 45 (c) 60 (d) 90
5. __________ drawing is often used to represent objects with circular or curved faces.
   (a) Orthographic (b) Isometric (c) Oblique (d) Linear
6. A table design is often represented using __________ projection.
   (a) Cavalier (b) Isometric (c) Orthographic (d) Cabinet
7. In Cabinet projection, the depth is __________ the length of the front view.
   (a) equal to (b) half of (c) twice (d) three times
8. The __________ view remains undistorted in oblique drawings.
   (a) side (b) front (c) top (d) depth
9. In Cavalier projection, the depth is drawn __________.
   (a) half size (b) full size (c) double size (d) quarter size
10. Oblique projection is used to represent __________ objects in a simple form.
    (a) 2D (b) complex (c) 3D (d) flat

Class Activity Discussion (FAQs)

1. What is an oblique drawing?
   Oblique drawing shows an object with the front face in full scale and the depth drawn at an angle.
2. What are the types of oblique drawing?
   There are two types: Cavalier and Cabinet projections.
3. Why is Cabinet projection more realistic than Cavalier projection?
   Because it reduces the depth to half scale, making the object appear more natural.
4. What is the purpose of oblique drawing?
   It helps show the full front view of an object along with some depth for easy visualization.
5. At what angle are the depth lines drawn in oblique drawings?
   The depth lines are drawn at 45 degrees.
6. How do you differentiate between Cavalier and Cabinet projections?
   Cavalier projection shows depth at full scale, while Cabinet projection shows depth at half scale.
7. What objects are commonly drawn using oblique projection?
   Objects like furniture, pipes, and simple household items.
8. Why is the front view undistorted in oblique drawings?
   To ensure accurate measurement and clarity of the main face.
9. Can curved surfaces be drawn using oblique drawing?
   Yes, it is suitable for objects with curved and circular shapes.
10. How is oblique drawing used in real life?
    It is used in product design, furniture sketches, and architectural illustrations.

Teacher’s Activities

1. Explain the two types of oblique projection (Cavalier and Cabinet).
2. Demonstrate the construction of a simple box using oblique drawing.
3. Provide examples of objects that can be drawn using oblique projection.

Learners’ Activities

1. Draw a box using both Cavalier and Cabinet projections.
2. Identify objects around them that could be represented using oblique drawing.
3. Compare their oblique drawings with isometric ones.

Evaluation Questions

1. Define oblique drawing.
2. List the two types of oblique projection.
3. What is the difference between Cavalier and Cabinet projections?
4. At what angle are depth lines drawn in oblique drawing?
5. Give two examples of objects drawn using oblique projection.
6. Why is the front view drawn in full scale in oblique projection?
7. What type of projection reduces the depth by half?
8. What drawing technique shows all three dimensions on one view?
9. How does oblique projection compare to isometric drawing?
10. Mention one real-life application of oblique drawing.

Conclusion

The teacher reviews students’ drawings and provides feedback on their accuracy and understanding. Corrections are made where necessary.