Drawing Instruments, Uses and Basic Drawing Practice for JSS 1

Workshop Processes: Drawing practice

Performance Objectives

By the end of the lesson, students should be able to:

1. identify drawing instruments and materials;
2. demonstrate correct techniques for handling drawing instruments and materials;
3. construct shapes with drawing instruments and materials;
4. care for drawing instruments and materials.

Introduction to Drawing Instruments and Materials

Technical drawing is a universal language used by engineers, architects and designers to communicate ideas clearly. To produce accurate and neat drawings, specific tools are required.

Drawing instruments are specialized, reusable tools used to guide the hand in creating precise lines, curves, angles and shapes on paper.

Drawing materials are consumable items that are used up or worn down during the drawing process.

The quality of a technical drawing depends heavily on the correct selection, handling and maintenance of these instruments and materials.

Identification and Uses of Drawing Instruments

Each drawing instrument has a specific function. Understanding these functions ensures that drawings are constructed accurately and efficiently.

The T-Square

A T-square consists of two main parts: a wooden or plastic blade and a stock. The stock is held firmly against the edge of the drawing board, allowing the blade to slide up and down.

The primary uses of the T-square are:

1. To draw horizontal lines.
2. To act as a base or support for set-squares when drawing vertical or inclined lines.

Set-Squares

Set-squares are triangular drawing instruments made of transparent plastic. They come in pairs with specific angles.

The two types of set-squares are:

1. The 45-degree set-square, which has angles of 45°, 45° and 90°.
2. The 30/60-degree set-square, which has angles of 30°, 60° and 90°.

Set-squares are used to draw vertical lines, diagonal lines at specific angles, and parallel or perpendicular lines when combined with a T-square.

Pair of Compasses

A compass is an instrument with two legs joined at the top by a hinge. One leg ends in a sharp metal point, while the other leg holds a pencil lead or a pencil.

The primary uses of a pair of compasses are:

1. To draw circles of various sizes.
2. To draw arcs and construct angles.
3. To transfer measurements from a ruler to the drawing paper.

Pair of Dividers

A divider looks similar to a compass, but both of its legs end in sharp metal points.

The primary uses of a pair of dividers are:

1. To transfer distances from one part of a drawing to another.
2. To divide a straight line or an arc into equal parts.
3. To step off equal measurements along a line.

French Curves

French curves are plastic templates with various curved edges. Unlike a compass, which draws perfect circular arcs, French curves are used to draw irregular, non-circular curves by connecting a series of plotted points smoothly.

Protractor

A protractor is a semi-circular or circular instrument made of transparent plastic, graduated in degrees from 0° to 180° or 360°.

The primary uses of a protractor are:

1. To measure existing angles on a drawing.
2. To lay out or plot angles that cannot be easily drawn with set-squares.

Ruler

A standard drawing ruler is a straightedge graduated in millimetres and centimetres.

The primary uses of a ruler are:

1. To measure straight distances.
2. To draw straight lines when a T-square is not being used.

Identification and Uses of Drawing Materials

Drawing materials are the consumables that support the drawing process. They must be selected carefully to maintain drawing quality.

Drawing Board

A drawing board is a flat, smooth wooden board with a straight working edge on the left side. It provides a rigid surface for supporting the drawing paper.

Drawing Paper

Drawing paper is the surface upon which the drawing is made. Standard sizes for school use include A3 and A4 paper. The paper must have a smooth texture and be strong enough to withstand erasing without tearing.

Drawing Pencils

Pencils are graded according to the hardness or softness of their lead. The grade is indicated by letters and numbers on the pencil body.

The main categories of drawing pencils are:

1. Hard pencils (such as 2H, 3H or 4H), which produce thin, light lines. These are used for initial construction lines and layout work.
2. Medium pencils (such as H or HB), which produce moderately dark lines. These are used for lettering, object outlines and border lines.
3. Soft pencils (such as B or 2B), which produce dark, thick lines. These are generally avoided in technical drawing because they smudge easily.

Eraser and Shield

An eraser is used to remove unwanted pencil lines. A soft, high-quality vinyl eraser is preferred because it does not smudge the paper. An erasing shield is a thin metal or plastic plate with various openings, used to protect correct lines while erasing nearby mistakes.

Masking Tape or Clips

Masking tape or drawing paper clips are used to secure the drawing paper firmly to the drawing board. This prevents the paper from moving while drawing.

Handling and Manipulation Techniques

Correct handling of drawing instruments prevents damage to the tools and ensures high precision in drawing work.

Setting Up the Drawing Paper

The procedure for securing drawing paper to the drawing board involves the following steps:

1. Place the drawing board flat on the table.
2. Place the drawing paper near the top-left corner of the board.
3. Slide the stock of the T-square firmly against the left edge of the drawing board.
4. Align the top edge of the drawing paper with the top edge of the T-square blade.
5. Hold the paper in place and stick pieces of masking tape on the top two corners of the paper.
6. Smooth the paper downwards and secure the bottom two corners with masking tape.

Manipulating the T-Square and Set-Squares

The T-square must always be operated from the left edge of the drawing board (for right-handed users). The stock must be held tightly against the board edge with the left hand, while the right hand is used to draw lines along the blade.

To draw vertical or angled lines, a set-square is placed on top of the T-square blade. The left hand holds both the T-square and the set-square firmly in position, while the right hand guides the pencil along the edge of the set-square.

Handling Pencils and Drawing Lines

Pencils should be sharpened to a conical point for general drawing, or a chisel point for drawing long straight lines. When drawing a line, the pencil should be inclined at an angle of about 60 degrees to the paper in the direction of the line. The pencil should be rotated slowly between the fingers while drawing to ensure even wear of the lead and a uniform line thickness.

Constructing Shapes with Drawing Instruments

Using drawing instruments correctly allows for the construction of precise geometric shapes. Below are the procedures for constructing basic shapes.

How to Construct a Square

A square has four equal sides and four 90-degree angles. The construction of a square with a given side length involves the following steps:

1. Place the T-square on the drawing board and draw a horizontal line of the required length, labeling the endpoints A and B.
2. Place a 45-degree or 30/60-degree set-square on top of the T-square blade.
3. Align the vertical edge of the set-square with point A and draw a vertical line upwards.
4. Align the vertical edge of the set-square with point B and draw a vertical line upwards.
5. Use a ruler or a pair of compasses to measure the distance AB.
6. Mark this same distance along the vertical line from A to find point D, and along the vertical line from B to find point C.
7. Use the T-square to draw a horizontal line connecting point D and point C to complete the square ABCD.

How to Construct a Triangle

An equilateral triangle has three equal sides and three 60-degree angles. The construction of an equilateral triangle with a given side length involves the following steps:

1. Draw a horizontal base line of the required length using a T-square, and label the endpoints A and B.
2. Adjust a pair of compasses so that the distance between the metal point and the pencil point is exactly equal to the length of the line AB.
3. Place the metal point of the compass on point A and draw an arc above the line.
4. Without changing the compass width, place the metal point on point B and draw another arc that intersects the first arc. Label the intersection point C.
5. Use a ruler to draw straight lines connecting point A to point C, and point B to point C to complete the triangle ABC.

How to Construct a Circle

A circle is a closed curve where all points on the boundary are at an equal distance (the radius) from a fixed center point. The construction of a circle of a given radius involves the following steps:

1. Mark a small cross on the paper to represent the center point of the circle, and label it O.
2. Place a ruler flat on the paper.
3. Place the metal point of a pair of compasses on the zero mark of the ruler, and adjust the pencil leg until the pencil point aligns with the required radius measurement.
4. Place the metal point of the compass firmly on the center point O.
5. Hold the handle at the top of the compass between the thumb and index finger.
6. Rotate the compass smoothly in a clockwise direction, letting the pencil point lightly touch the paper to draw a complete, continuous circular line.

Care and Maintenance of Drawing Instruments

Drawing instruments are delicate and expensive. Proper care ensures their accuracy and extends their lifespan.

Important care and maintenance rules include:

1. Clean all plastic instruments, such as T-squares, set-squares and protractors, regularly with a damp cloth and mild soap to remove dirt and graphite dust.
2. Never use a penknife or razor blade to cut paper against the edge of a T-square or set-square, as this will damage the straight edges.
3. Keep the metal points of compasses and dividers protected when not in use to prevent them from becoming blunt or causing injury.
4. Avoid dropping drawing instruments, as impact can crack plastic tools or bend the metal legs of compasses and dividers.
5. Store all drawing instruments in a protective case or box when they are not in use.
6. Keep hands clean and dry while drawing to prevent smudging the paper and rusting metal tools.
7. Do not use drawing pencils for non-drawing purposes, such as poking holes or tapping on desks, as this breaks the internal lead.

Summary of Drawing Instruments and Materials

The table below summarizes the key drawing instruments, materials and their primary functions.