Lesson Notes By Weeks and Term v4 - JHS 1

Lesson Video

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Performance objectives

• Identify and describe four types of lines.
• Understand how lines convey messages.
• Create a simple design using different lines.
• Explain the importance of line types.

Lesson summary

Welcome, learners! In our last lesson, we learned about the importance of designing before making an object. But how do we show our design ideas to others clearly? Imagine you want a carpenter to build you a new table. If you just describe it with words, they might build it differently from what you imagined. However, if you draw it, they will know exactly what you want. In technical drawing, we use a special "language" to communicate ideas perfectly. This language is not made of words but of different types of lines. Each line has a specific meaning, just like each word in English or Twi has a meaning.

Lesson notes

In graphic communication (like technical drawing), we use different types of lines to represent different features of an object. Using the correct lines makes a drawing clear and easy to understand. Let's explore the most important ones. The Alphabet of Lines

Think of these lines as the alphabet you use to write a sentence. Each one has a job. Object Line (or Visible Outline) Appearance: This is a very thick and dark continuous line. It is the darkest line on a drawing. Purpose: It is used to show the main shape and visible edges of an object. When you look at an object, the edges you can see are drawn with object lines. Example: Imagine drawing a box of chalk. The lines you draw to show the top, bottom, and sides that you can see are all object lines. Hidden Line Appearance: This is a medium-thick line made of short, evenly spaced dashes. Purpose: It is used to show edges, corners, or surfaces of an object that are hidden from our view. Example: Imagine our box of chalk is closed, but we know there are pieces of chalk inside. If we wanted to show where the chalk is inside the box, we would use hidden lines. Another example: If you draw a cup, the inner bottom edge is hidden from the side view, so you would use a hidden line to show it. Centre Line Appearance: This is a thin line made of alternating long and short dashes. It always starts and ends with a long dash. Purpose: It is used to show the centre of circles, arcs, and symmetrical objects. It helps to locate the middle of a feature. Example: When drawing a car tyre, a Milo tin, or a round kitchen stool, you would use centre lines (one horizontal, one vertical) crossing at the exact middle to show the centre point. Dimension Line Appearance: This is a thin, continuous line with an arrowhead at each end. It has a space in the middle for a number (the measurement). Purpose: It is used to show the size or distance of a feature on a drawing. It tells you how long, wide, or tall something is. Example: To show that the length of a book is 20 cm, you would draw a dimension line parallel to the book's edge with "20 cm" written in the middle. Extension Line (or Projection Line) Appearance: This is a thin, continuous line that extends from the object. There is a small gap between the object line and the start of the extension line. Purpose: It is used together with dimension lines. It shows exactly where a dimension starts and ends. Example: When you are dimensioning the book, the two extension lines would be drawn from the corners of the book outwards, and the dimension line would be drawn between them.

*(See the image for Dimension Line above; the short vertical lines are Extension Lines)* Construction Line Appearance: This is a very light and thin continuous line. It is drawn so lightly that it can be easily erased or is barely visible on the final drawing. Purpose: It is used for laying out a drawing. It helps you to plan where everything will go before you draw the final thick object lines. They are guides. Example: Before drawing a perfect square, you might first draw very light construction lines to guide your ruler and pencil. Once you are happy, you would trace over them with dark object lines.

Guided Practice (With Solutions)