March 28, 2024

Drawing plays a significant role in the expression of thought and ideas. Often, descriptions which cannot be fully expressed in words, are made clearer with the use of drawings. Thus, drawing is similar to a language. However, unlike a language where words are the means of expressing ideas; lines, points, and shapes are usually employed in the case of drawings.

 

Definition of Technical Drawing

There are several kinds of drawings. The kind most relevant to technology comprises those referred to as technical drawings.

As a subject technical drawing is defined as a standard way of expressing technical information through the use of lines and points. Such technical information is usually about machine parts and components, building plans, infrastructure (roads, bridges, dams and others), plumbing works, electric devices, home appliances and so forth.

Technical drawing is also variously known by such names as machine drawing, engineering drawing, and drafting. In technical drawing, a point represents a position. A line, defined as a collection of points joined end to end, represents a distance. Combinations of lines can also be used to represent areas and volumes. Both straight and curved lines are used.

You should note that technical drawing is clearly different from fine art. In fine art, use is made of very dark lines with bold pencils, various colours and most especially an effect showing the direction of light is created on the object. In contrast, technical drawing uses only faint or moderately thick lines made with pencils producing thin marks. No contrast in the intensity of light is shown on technical drawings. Also no colouring is shown on technical drawings.

Sets of instruments and materials used in technical drawing exist. They are all made with the objective of helping the user to produce very accurate drawings. The basic set of equipment is enumerated as follows.

1) Drawing board and Tee-square

The drawing board provides a smooth, flat surface on which technical drawings are made. Drawing boards fall into two classes namely the portable types and the stationary types. Two portable types are the Half imperial (length 585mm, breath 452mm) and the Full imperial (Length 812mm, breadth 585mm). These sizes are suitable for use by secondary school students.

Stationary types are basically drawing tables. They are bulky and are usually fitted with accompanying gadgets such as lamps, seat and scales. These are used at higher levels of technical education.

The tee-square obtains its name from its shape. Its function is to provide horizontal reference lines on the paper. The crossbar of the tee-square by which the equipment is held is called stock. Tee-squares are often made with graduations along their edges (called blades).

The most widely used material for making drawing board and tee-square is wood. Plastics, and to a much lesser extent metals are also used.

 

2) Drawing Paper and Sticker Tape

Drawing paper is the sheet on which lines, arcs and letters, which constitute the drawings, are drawn. Various standard sizes are available. Drawing paper is sometimes made as a big sheet, which may be easily cut to any desired size. Drawing is made only on one face of the paper. Two popular types of drawing sheets are the white-coloured paper and the tracing paper. All forms of drawings can be made on the two types. The latter type is translucent and is therefore well suited for tracing drawings. This significantly aids accurate duplication. The printing paper is also part of technical drawing materials. The printing paper is used when drawings made on tracing paper are to be printed as permanent blueprints on paper.

A sticker or adhesive tape is required for pasting the paper on the board. Pins should not be used for this purpose because they can damage the surface of the board.

 

3) Pencils

Drawing pencils are made in two series namely the B and H series. The B series constitutes soft pencils, which make very dark and bold marks on paper. These are much used in fine art drawings and are not suitable for technical drawings. The H series constitutes the hard pencils which when used, produce faint and usually thin marks. This is the series of pencils used in technical drawings.

The H series of pencils is denoted as H, 2H, 3H, 4H, 5H, 6H, 7H, 8H and 9H. The higher the number, the harder is the pencil and therefore the fainter its marks. For the B series of pencils, the higher the number, the softer is the pencil and hence the bolder the mark that it makes. The B series of pencils are not useful in technical drawing. In drawing, for general sketching or rough work, the ideal option is the HB pencil, which is halfway between the two series.

A pencil should always be sharpened to a conical shape having a well-pointed tip. A flat tip will sometimes produce double lines and thus should be avoided. A pencil is often wrongly called lead pencil. You should note that a pencil does not contain lead. It is made from a mixture of graphite, clay, wax and certain other chemicals. This wrong name arose from the fact that graphite used to be mistakenly called black lead.

 

4) Sharpener and Soft Eraser

A good sharpener or a smooth-edged sharp blade is part of the technical drawing equipment. Immediately the sharpener begins to get blunt, it should be changed.

A good eraser made from soft rubber is also needed. This eraser must be able to rub off pencil marks without leaving any mark on the paper. Along with an eraser, a small white cloth is also needed. This should be used exclusively for wiping the drawing paper as needed. The white colour aids easy detection of any dirt in the cloth. The cloth should be washed when required.

 

5) Set squares

A set square is a triangular-shaped object used in drawing lines at various angles to each other. Each set square has a right angle and angles of 45°, or 30° and 60°. Set squares are most commonly made of plastic. Wooden and metal types also exist.

A more useful set square is the adjustable set square. A wide range of angles can be obtained using this type. Set squares are usually made with graduations on the sides.

 

6) Scale Rule

A scale rule is used for making linear measurements. A common scale rule has a triangular cross-section and has graduations of two different scales on each of its three sides. This greatly helps when making scale drawings. In the absence of a scale rule, a ruler can be employed for linear measurements. Because a ruler is usually graduated on one scale its use makes drawing with different scales quite sluggish.

 

7) Compasses and Dividers

A pair of compasses is needed for accurate drawing of regular arcs and circles. Also required is a pair of dividers. This is needed for transferring measurements. The fact that pins are used on the dividers ensures that no pencil marks are left on the paper in the course of transfer

 

8) Protractor

A protractor is used for measuring angles. It may be circular or semi-circular in shape. The latter can measure angles between 0 and 180 degrees while the former can measure angles between 0 and 360 degrees.

 

9) French Curve and Flexicurve

The purpose of a French curve is for drawing irregular arcs. There are two different types namely; the rigid French curve and the flexicurve. The rigid type has several different curves inscribed on it. Rigid French curves are often made in sets. This allows a full range of curves to be drawn. The flexicurve is a rubber cord, which can be easily bent to suit the shape of the desired arc or curve. The French curve or flexicurve, compasses and set squares are all used together with a pencil.

To produce good technical drawings, you must take note of the following points.

  1. Use the drawing equipment that is in good condition and you must use them rightly.
  2. Draw neatly, and
  3. Practice your drawings regularly.

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