Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Produce neat, proportional freehand sketches.
• Add accurate dimensions using SANS 10111 standards.
• Use leader lines and notes to clarify features.
• Select and apply correct dimensioning units (mm).
• Evaluate the quality and accuracy of sketches.

Lesson summary

Freehand drawing and dimensioning form the foundation of effective communication in engineering and design. Imagine planning a new school building in a growing township like Khayelitsha. Architects and engineers need to quickly sketch ideas, modifications, and specific measurements during site meetings. Without a solid grasp of freehand drawing to visually represent concepts and accurate dimensioning to communicate sizes precisely, projects would be delayed, costly, and prone to errors. These skills aren't just theoretical; they are practical tools used every day by professionals who shape our environment. This week, we'll focus on mastering these essential skills.

Lesson notes

2.1 Freehand Sketching: Freehand sketching is the art of creating drawings without the aid of instruments like rulers, compasses, or set squares. It's about conveying ideas quickly and effectively. Focus on proportion – the relative size of parts in relation to each other and the whole object. Lightly sketch outlines first, establishing the overall shape before adding detail.

Line Quality: Use a soft pencil (e.g., 2B) to create lines that can be easily erased and adjusted. Strive for consistent line thickness and darkness. Varying line weight can emphasize certain features. For example, outlines can be slightly thicker than internal details.

Geometric Shapes: Practice sketching basic geometric shapes. Start with squares and rectangles. Mentally divide the space into equal parts to ensure accurate proportions. For circles, imagine a square and sketch the circle within it, touching the square at four points. For triangles, establish the base and height, then connect the apex to the base ends. 3D Objects: Start with cubes. Sketch a square, then draw three lines extending back from the corners, all at the same angle. Connect these lines to form the back faces of the cube. Cylinders are essentially circles extended in the third dimension. Sketch two circles, one above the other, and connect them with two parallel lines. Prisms are similar to cubes but with different polygonal bases.

Example 1: Sketching a cellphone: Outline: Lightly sketch a rectangle that approximates the overall dimensions of a cellphone.

Screen Area: Divide the rectangle to indicate the screen area, camera position, and speaker location.

Details: Add details such as buttons, camera lenses, and speaker grills. Remember to maintain the relative proportions. Round the corners slightly to simulate the curved edges.

Line Weight: Darken the outlines and important features to make them stand out. 2.2 Dimensioning: Dimensioning is the process of adding measurements to a drawing to define the size and location of its features. Accuracy and clarity are paramount. We follow the South African National Standard SANS 10111, which is based on ISO standards.

Dimension Lines: Thin, continuous lines terminated by arrowheads at each end. The dimension value is placed above (or inline with) the dimension line, usually near the center.

Extension Lines (Witness Lines): Thin, continuous lines that extend from the object to the dimension line. They should start slightly off the object outline (a small gap) and extend slightly beyond the dimension line.

Arrowheads: Should be neat, filled in, and proportional to the size of the drawing.

Dimension Text: Should be clear, legible, and placed above or inline with the dimension line. Use a consistent font and size throughout the drawing. Use millimeters (mm) unless otherwise specified. Meters (m) may be appropriate for large structures. Do NOT include the "mm" symbol after each dimension value. The general note "All dimensions in millimeters" should be placed near the title block.

Leader Lines: Thin lines with an arrowhead pointing to a specific feature. They are used to attach a local note to the drawing.

General Rules: Dimensions should be placed outside the object whenever possible. Avoid crossing dimension lines or extension lines. Dimension hidden lines unless they are crucial to understanding the part. Dimension each feature only once. Place dimensions in a clear and organized manner.

Example 2: Dimensioning a rectangular block: Imagine a rectangular concrete block used in building construction. It's 200mm long, 100mm wide, and 50mm high. Sketch the rectangular block freehand. Draw extension lines extending from each side of the rectangle. Draw dimension lines parallel to each side, extending between the extension lines. Add arrowheads to the ends of the dimension lines. Write the dimension values (200, 100, 50) above the dimension lines, near the center.

Add a general note: "All dimensions in millimeters".

Example 3: Dimensioning a circular hole in a plate: Imagine a metal plate with a hole drilled through it. The plate is 150mm long and 80mm wide. The hole is in the center and has a diameter of 20mm. Sketch the rectangular plate freehand. Sketch the circular hole in the center of the plate. Dimension the length and width of the plate as in Example

2. Use a leader line to point to the circular hole. Write "Ø20" (the diameter symbol followed by the diameter value) at the end of the leader line. Guided Practice (With Solutions)

Question 1: Sketch a freehand drawing of a square prism with sides of 50mm and a height of 80mm. Add dimensions to indicate the size of the prism. Assume all dimensions are in millimeters.

Solution: Sketch the square prism freehand, trying to maintain proportional sides and height. Draw extension lines extending from the sides and the top of the prism. Draw dimension lines parallel to the sides and the top, connecting the extension lines with arrowheads.