Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Identify and correctly use at least 5 drawing instruments.
• Apply standard lettering techniques for legible text.
• Differentiate and draw at least 5 different line types according to SANS 10111 standards.
• Construct basic geometric shapes accurately.
• Apply appropriate line weights for clarity.

Lesson summary

This week, we delve into the foundational elements of Engineering Graphics and Design (EGD): drawing instruments, lettering, and line types. Mastering these skills is crucial for creating clear, accurate, and professional technical drawings. These drawings serve as a universal language for engineers, architects, and technicians. Think about the blueprints for a new RDP house, the plans for a bridge connecting communities, or the designs for a locally manufactured solar panel – all these rely on precisely executed technical drawings. In South Africa, where infrastructure development and manufacturing are essential for economic growth, a solid understanding of these basics is indispensable.

Lesson notes

2.1 Drawing Instruments Pencils: The cornerstone of EG

D. Hardness Grades: Understanding pencil hardness is crucial. Hard pencils (e.g., 2H, 4H) create light, fine lines ideal for construction lines. Soft pencils (e.g., HB, 2B) produce darker, thicker lines suitable for visible outlines and lettering. Using the correct pencil grade ensures accuracy and prevents smudging.

Sharpening: A properly sharpened pencil, with a conical point, is essential for precise line work. Pencil pointers are designed to achieve this. A dull pencil results in thick, uneven lines.

Set Squares: Used for drawing vertical and angled lines. Commonly available in 45°/45°/90° and 30°/60°/90° configurations. Using them in combination allows you to draw lines at 15° intervals.

Example: To draw a line at 30 degrees, use the 30/60/90 set square. Align the hypotenuse (longest side) of the set square with your horizontal reference line (T-square or drawing board edge) and draw along the 30-degree edge.

T-Square: Used primarily for drawing horizontal lines. The head of the T-square rests firmly against the edge of the drawing board, providing a stable reference.

Important: Make sure the drawing board edge is straight and true!

Compass: Essential for drawing circles and arcs. The compass should be adjusted carefully to the desired radius.

Example: To draw a circle with a radius of 25mm, set the distance between the compass point and the pencil lead to 25mm using a ruler or scale. Place the compass point at the desired center of the circle and rotate the compass to draw the circle.

Dividers: Used for transferring measurements and dividing lines into equal segments. They have two points, unlike a compass which has a point and a pencil lead.

Example: To divide a line into 5 equal segments, set the dividers to an estimated distance. Step off the distance along the line. Adjust the divider opening until you can step off the distance exactly 5 times.

Scales: Used for accurately measuring and transferring dimensions from drawings to real-world objects or vice versa. Different scales (e.g., 1:100, 1:50) represent different ratios between the drawing and the actual size.

Example: A scale of 1:100 means that 1 unit on the drawing represents 100 units in real life. So, if a wall is 5 meters long in reality, it will be represented as 5 cm on the drawing at a scale of 1:100 (5m = 500cm; 500cm / 100 = 5cm).

Eraser: Used for correcting mistakes. Soft erasers are generally preferred as they are less likely to damage the drawing paper.

Drawing board: A flat, stable surface on which to create your drawings. 2.2 Lettering Single-Stroke Gothic: The standard lettering style used in EGD due to its legibility and simplicity.

Principles: Uniform Height: All letters should be the same height.

Uniform Width: Letters should have a consistent width, except for letters like "I" and "W." Vertical or Inclined: Lettering can be vertical or inclined (at an angle of approximately 75 degrees).

Consistent Spacing: Maintain consistent spacing between letters and words.

Guidelines: Use light guidelines (drawn with a hard pencil) to ensure uniform letter height and baseline. Erase the guidelines after lettering.

Importance: Clear and legible lettering is crucial for conveying information accurately on technical drawings. Poor lettering can lead to misinterpretations and errors.

Example: Practice writing the alphabet and numbers using the single-stroke Gothic style. Pay attention to letter formation and spacing. A good starting height for lettering is 5mm. 2.3 Line Types Different line types are used to represent different features on a drawing. SANS 10111 (South African National Standard) specifies the standards for line types.

Visible Lines (Thick Continuous Line): Represent the visible edges and outlines of an object. Drawn with a thicker pencil (e.g., HB, 2B).

Hidden Lines (Dashed Line): Represent edges and outlines that are hidden from view. Drawn with a thinner pencil (e.g., H, 2H). The dashes should be evenly spaced.

Center Lines (Long-Short Dashed Line): Indicate the center of a circle, arc, or symmetrical object. The long dash should be longer than the short dash. They should extend slightly beyond the feature they are referencing. Dimension Lines (Thin Continuous Line with Arrows): Indicate the size of an object or feature. Arrows are placed at the ends of the dimension line, pointing to the extension lines.

Extension Lines (Thin Continuous Line): Extend from the object to the dimension line, indicating the extent of the dimension. They should start slightly away from the outline of the object. Cutting Plane Line (Thick Dashed Line with Arrows): Indicates the location of an imaginary cut through an object to show the internal features in a section view. The arrows point in the direction of viewing. Construction Lines (Very Thin Continuous Line): Light lines used for constructing the drawing.