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

• Identify and correctly use a range of drawing instruments.
• Apply correct lettering techniques as per SANS standards.
• Differentiate and accurately apply various line types.
• Produce a simple engineering drawing using these skills.

Lesson summary

Engineering Graphics and Design (EGD) relies on clear and precise communication. This week, we delve into the fundamental tools, lettering styles, and line types that form the backbone of all technical drawings. Mastering these elements allows you to create accurate, unambiguous drawings understood by engineers, architects, builders, and other professionals across South Africa and globally. From designing a simple house extension in Khayelitsha to planning complex infrastructure projects like the Gautrain expansion, clear communication through EGD is crucial for success and safety.

Lesson notes

2.1 Drawing Instruments Pencils: Different grades of pencils are used in EGD. Harder pencils (e.g., 2H, H) are used for light construction lines and accurate details because they produce fine, light lines that are easy to erase. Softer pencils (e.g., HB, B, 2B) are used for object lines, lettering, and shading because they produce darker, bolder lines. Always use the correct grade for the intended purpose.

Important: Always rotate the pencil slightly as you draw to maintain a consistent line thickness.*

Example: Use a 2H pencil to draw the layout lines for a floor plan and a B pencil to draw the final outline of the walls.

Erasers: Soft, non-abrasive erasers are crucial for removing pencil lines without damaging the drawing paper. Avoid using hard erasers, as they can tear the paper and leave smudges. An erasing shield can be used to erase specific lines without affecting adjacent details.

Example: Use an erasing shield to carefully remove a dimension line without erasing the adjacent extension lines.

Set Squares: Typically 45° and 30°/60° set squares are used to draw vertical, horizontal, and inclined lines accurately. They are often used in combination with a T-square or parallel motion drafting board.

Example: Use the 45° set square to draw diagonal lines for a roof pitch on a house elevation drawing. Use in conjunction with a tee square to ensure correct angles.

Compasses: Used to draw circles and arcs. They consist of a point that is fixed to the paper and a pencil lead that rotates around the point.

Example: Use a compass to draw a circular swimming pool in a site plan. Ensure the pencil lead is sharpened to a fine point.

Dividers: Similar to compasses, but with two points instead of a point and a pencil lead. Used to transfer dimensions or divide lines into equal segments.

Example: Use dividers to accurately transfer a measurement from a scale ruler to your drawing.

Drawing Board: A stable, flat surface is essential for accurate drawing. A drawing board provides this surface and often includes a T-square or parallel motion bar for drawing horizontal lines. The surface of the board should be smooth and free of any imperfections.

Example: Using a drawing board with a parallel motion bar ensures that all horizontal lines drawn are perfectly parallel. 2.2 Lettering Lettering in EGD must be clear, legible, and consistent. Single-stroke vertical capital letters are typically used. SANS (South African National Standards) specifies guidelines for letter height, spacing, and line thickness.

Principles: Consistency: Maintain uniform letter height and spacing throughout the drawing.

Legibility: Ensure that letters are clearly formed and easy to read.

Spacing: The space between letters and words should be consistent.

Guidelines: Use light guidelines (drawn with a hard pencil) to ensure uniformity. Erase these after lettering.

Example: For a title block, use a letter height of 5mm and a line thickness of 0.5mm.

The title might be: "PROPOSED HOUSE EXTENSION". 2.3 Line Types Different line types represent different features in a technical drawing. Understanding these conventions is essential for accurate interpretation. According to SANS 10111, common line types include: Visible Lines (Object Lines): Thick, continuous lines used to represent the visible edges of an object. They indicate the shape and outline of the object.

Example:* The outline of a building on a plan.

Hidden Lines: Thin, dashed lines used to represent edges that are hidden from view. They provide information about features that are not directly visible.

Example:* A pipe running behind a wall.

Centre Lines: Thin, long-dashed, short-dashed lines used to indicate the centre of a circle, arc, or symmetrical feature.

Example:* The centre of a circular window.

Dimension Lines: Thin, continuous lines with arrowheads at each end, indicating the extent of a dimension. They are placed outside the object being dimensioned.

Example:* The length of a wall on a floor plan.

Extension Lines: Thin, continuous lines that extend from the object being dimensioned to the dimension line.

Example:* Lines extending from the walls to the dimension lines showing wall length.

Cutting Plane Lines: Thick, dashed lines with arrows indicating the direction of the view. Used to show where a section view has been taken.

Example:* Indicating where a section view of a building has been taken to show internal details.

Construction Lines: Very light lines, drawn using a hard pencil (e.g., 2H, 4H). Used for setting out the drawing and are erased after the drawing is complete.

Example:* Initial layout lines for a complex geometric shape.