Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Identify and use at least 5 different types of lines according to SANS 10111.
• Construct neat single-stroke vertical capital lettering.
• Select the appropriate line type for a given feature.
• Explain the purpose of different line weights (thicknesses).
• Produce a drawing combining accurate line types and lettering.

Lesson summary

Welcome, Grade 10 learners! This week, we delve deeper into the essential tools and techniques that form the bedrock of Engineering Graphics and Design (EGD). Mastering drawing instruments, understanding lettering conventions, and skillfully applying different line types are not just academic exercises. These skills are crucial for clear communication in various fields, from architecture and civil engineering to manufacturing and even graphic design. Imagine designing a new taxi rank in your community, planning the layout of a sustainable farm, or creating detailed instructions for assembling furniture made in South Africa.

Lesson notes

2.1 Line Types and Conventions (SANS 10111) Lines are the alphabet of engineering drawings. Different line types convey different information about the object being represented. In South Africa, we adhere to the SANS 10111 standard for technical drawings, which dictates the types of lines to be used and their applications. Here are some of the most common line types you will encounter: Visible Outline (Continuous Thick): Used to represent the visible edges and outlines of the object. This is the "main" line of your drawing. Use a 0.5mm or 0.7mm pen for this. Think of it as the solid edge you would see if you held the object in your hand.

Hidden Detail (Dashed Medium): Used to represent edges and surfaces that are hidden from view. These lines are typically 3mm dashes with 1mm gaps. Use a 0.3mm or 0.5mm pen. They help you understand the internal structure of an object without having to cut it open. Imagine looking at a solid brick wall. Hidden detail lines could show you the mortar lines between the bricks on the other side.

Center Line (Long Dash Dot Dash Thin): Used to indicate the center of a symmetrical shape, such as a circle, cylinder, or hole. The dashes are typically 10-20mm long, the dots are short, and the gaps are about 1-2mm. Use a 0.3mm pen. These lines are crucial for correctly positioning features on your drawing.

Dimension Line (Continuous Thin): Used to indicate the extent of a dimension, terminated by arrowheads that touch the extension lines. Use a 0.25mm or 0.3mm pen. The dimension value is placed above (or sometimes within) the dimension line.

Extension Line (Continuous Thin): Used to extend a point or line from the object to the dimension line. They extend slightly beyond the dimension line. Use a 0.25mm or 0.3mm pen. Cutting Plane Line (Long Dash Double Dot Dash Thick): Used to indicate the location of an imaginary cut through the object for a sectional view. Arrowheads at the ends of the line show the direction of sight. This line is thicker than a center line and typically heavier than a visible outline.

Line Weight (Thickness): The thickness of a line, also known as its weight, is crucial for visual clarity. Thicker lines emphasize important features (like visible outlines), while thinner lines are used for less prominent features (like dimension lines). Using different pen sizes (e.g., 0.7mm for visible outlines, 0.3mm for hidden detail and center lines) helps achieve this effect. Consistent line weight makes your drawings easier to understand.

Worked example

Imagine you're drawing a rectangular block with a circular hole through the center.

The visible outlines of the rectangular block would be drawn using a continuous thick line (e.g., 0.7mm pen).

The edges of the hole that are hidden inside the block would be represented by dashed medium lines (e.g., 0.3mm pen).

A center line (long dash dot dash thin, 0.3mm pen) would be drawn through the center of the hole, indicating its position.

Dimension and extension lines (continuous thin, 0.25mm pen) would be used to indicate the size and position of the hole and the block.

2.2 Lettering Conventions

Technical drawings require clear, consistent, and legible lettering. Single-stroke vertical capital lettering is the standard for most engineering drawings. This means each letter is formed with a single, consistent stroke of the pen, and the letters are upright (vertical).

Key Principles for Good Lettering:

Height: All letters should be the same height. Common heights are 3.5mm or 5mm. Use a ruler or lettering guide to ensure consistency.

Width: Letters should have a consistent width, generally about 2/3 to 3/4 of their height (except for narrow letters like 'I').

Spacing: The space between letters should be uniform and visually appealing. Avoid overcrowding or excessive gaps. A good rule of thumb is to leave a space roughly equal to the thickness of the line used to draw the letters.

Consistency: Maintain a consistent style throughout the drawing.

Legibility: The primary goal is to ensure the lettering is easy to read.

Practice Tips:

Use light guidelines to maintain consistent height and spacing. These guidelines can be erased after the lettering is complete.

Practice regularly to develop muscle memory and improve your technique.

Use a sharp pencil or technical pen for crisp, clean lines.