The verbal information, in writing, given in the drawing is known as lettering. Lettering plays an important role as far as logical comprehension of the drawing is concerned, particularly for those parts of the drawing which cannot be shown by lines. A well meaning drawing must be associated with clean dimensioning with good letter quality. Therefore, lettering should be lucid, legible and uniform in appearance and easy-to-write for rapid freehand writing. The art of writing letters such as alphabets and numbers etc. is known as lettering. Lettering forms an important part of drawing and is used to write letters, dimensions, notes and such other necessary information as may be required for complete execution of the drawing of an object.
Certain principles need to be followed for developing good writing skill for lettering. One must have knowledge of the following parameters in order to master the art of good lettering.
- Shape and proportion of each letter
- Order and direction of the stroke
- General composition of letters
- Rules for combining letters into words
- Skill of writing the letters in plain and simple style so that the lettering can be done freehand
Letter Styles
Letter styles are generally classified as Gothic, Roman, Italic and Text. They were all made with speedball pens and are therefore largely single-stroke letters. If the letters are drawn in outline and filled in, they are referred to as “filled- in” letters. The plainest and most legible style is the Gothic from which the single-stroke engineering letters are derived. The term roman refers to any letter having wide down ward strokes and thin connecting strokes. Roman letters include old roman and modern roman, and may be vertical or inclined. Inclined letters are also referred to as italic, regardless of the letter style; text letters are often referred to as old English.
Depending upon the spacing between words and thickness of strokes, letters may be classified into two types.
1) Extended and Condensed Letters
To meet design or space requirements, letters may be narrower and spaced closer together, in which case they are called “Compressed” or “Condensed” letters. If the letters are wider than normal, they are referred to as “Extended” letters.
2) Light Face and Bold Face Letters
Letters also vary as to the thickness of the stems or strokes. Letters having very thin stems are called Light Face Letters, while those having heavy stems are called Bold Face Letters.
Single-Stroke Letters
The Bureau of Indian Standards (IS: 9609-1990) recommends single stroke lettering for use in engineering drawing. These are the simplest forms of letters and are usually employed in most of the engineering drawings. The word single stroke should not be misconstrued to mean that the letter should be made in one stroke without lifting the pencil. It actually means that the thickness of the line of letter should be such as it is obtained in one stroke of the pencil. The horizontal lines of letters should be drawn from left to right and vertical or inclined lines from top to bottom.
Single-stroke letters are of two types.
1) Vertical – Stem of vertical letters are perpendicular to the horizontal
2) Inclined - Inclined letters lean to the right, the slope being 75° with the horizontal.
According to the height of letters, they are classified as:
i) Lettering ‘A’
ii) Lettering ‘B’
In lettering ‘A’ type, the height of the capital letter is divided into 14 parts, while in lettering ‘B’ type, it is divided into 10 parts. The height of the letters and numerals for engineering drawing can be selected from 2.5, 3.5, 5, 7, 10, 14 and 20 mm according to the size of the drawing. The ratio of height to width varies but in case of most of the letters it is 6:5. The details of the characteristics of the types of lettering are given in Table 1 and Table 2.
Table 1 Characteristics of Type ‘A’ Lettering
Table 3 Different Sizes of Letters for Different Purposes
Fig. 2 Single-Stroke Vertical Capital Letters and Figures with Approximate Proportions
Fig. 3 Single-Stroke Inclined Capital Letters and Figures with Approximate Proportions
Fig. 5 Single-Stroke Inclined Lowercase Letters and Figures with Approximate Proportions
Single-stroke inclined capital letters and figures are shown in Fig. 3. The lower-case letters are usually used in architectural drawings. Vertical and inclined lower-case alphabets are shown in Fig. 4 and Fig. 5 respectively. The width of the majority of letters is equal to the height. All letters should be uniform in shape, slope, size, shade and spacing. The shape and slope of every letter should be uniform throughout a drawing. For maintaining uniformity in size, thin and light guide-lines may first be drawn and lettering may then be done between them. The shade of every letter must be the same as that of the outlines of drawings, i.e. intensely black. Therefore, H or HB grade of pencil is recommended for this purpose.
The spacing between two letters should not necessarily be equal. The letters should be so spaced that they do not appear too close together or too much apart. Judging by the eye, the background areas between the letters should be kept approximately equal. The distance between the words must be uniform and at least equal to the height of the letters. Lettering should be done as can be read from the front with the main title horizontal, i.e. when the drawing is viewed from the bottom edge. All sub-titles should be placed below but not too close to the respective views. Lettering, except the dimension figures, should be underlined to make them more prominent.
Gothic Letters
Gothic letters are formed by thickening the stems of single-stroke letters. These are mostly used for main titles of ink-drawings. The outlines of the letters are first drawn with the aid of instruments and then filled-in with ink. The thickness of the stem may vary from 1/5th to 1/10th of the height of the letters. Fig.6 shows the alphabets and figures in gothic with thickness equal to 1/7th of the height.
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