Lettering Styles Used in Engineering Drawing

Introduction

Writing of titles, dimensions, notes, and other important particulars on a drawing is called lettering. Lettering is an important part of a drawing. However accurate and neat a drawing may be drawn, its appearance is spoiled and sometimes, its usefulness is impaired by poor lettering.  Lettering should, therefore, be done properly in clear, legible and uniform style. It should be in plain and simple style so that it could be done free hand and speedily.

Style of Lettering

There are various forms of alphabets used in the art of lettering and each type is used for some particular purpose. ‘Old Roman’ style is the parent of all these styles. It is the basic standard for architects and artists. A variation of this style is known as ‘Modern Roman’ used by civil engineers, in maps and photo-graphical drawings. The simplified forms called ‘Commercial Gothic’ are used almost exclusively for working drawings. ‘Gothic’ letters are elementary strokes of even width. ‘Roman’ letters have elementary strokes “accented” or consisting of heavy and light lines. All slanting letters are classified as ‘Italics’.

Typical Stenciled Style
Typical Stenciled Style

Types of Lettering

Lettering may be drawn in various types. These are given below:

(a) According to the Height

  • Lettering ‘A’
  • 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 letters and numerals for engineering drawing are generally in the range of 2.5, 3.5, 5, 7, 10, 14 and 20 mm according to the size of drawing. (Refer Tables Below)

Table 1: Lettering ‘A’ (d=h/14)

Characteristic

Ratio

Dimensions (mm)

Lettering height of capitals

h

(14/14)h2.53.5571420
Height of lower case letters

c

(10/14)h2.53.5571014
Spacing between characters

a

(2/14)h0.350.50.711.422.8
Minimum spacing of base lines

b

(20/14)h3.55710142028
Minimum spacing between words

e

(6/14)h1.051.52.134.268.4
Thickness of lines

d

(1/14)h0.180.250.350.50.71

1.4

Table 2: Lettering ‘B’ (d=h/10)

Characteristic

Ratio

Dimensions (mm)

Lettering height of capitals

h

(10/10)h2.53.557101420
Height of lower case letters

c

(7/10)h  –2.53.55710

14

Spacing between characters

a

(2/10)h0.50.711.422.8

4

Minimum spacing of base lines

b

(14/10)h3.557101420

28

Minimum spacing between words

e

(6/10)h1.52.134.268.4

12

Thickness of lines

d

(1/10)h0.25 0.35 0.5 0.711.4

2

(b) According to the Proportion of Width and Height

  • Normal Letters. Normal letters have usual height and width and are used for general purpose written in usual space.
  • Compressed or Condensed Letters. Compressed or condensed letters are those which are written narrow in their proportion of width to height, i.e. height of these letters is more than the width. These are used when the space is limited.
  • Extended Letters. Extended letters are those which are written wide in their proportion of width to height, i.e. height of these letters is less or equal to the width.

Normal, Condensed and Extended Letters

(c) According to the Stem Thickness. Letters also vary in the thickness of the stems or strokes. Letters having very thin stems are called light face, while those having heavy stems are called bold face.

Light and Bold Face Letters

(d) According to the Stroke of Pencil

  • Single Stroke Letters. The thickness of the lines of the single-stroke letters is obtained in one stroke of the pencil.  This is the reason why these are called single stroke letters.  These letters being simple are usually employed in most of the engineering drawings.  Single stroke letters are of two types: (i) vertical (ii) inclined. Both vertical and inclined letters and numerals are suitable for general use.  One can resort to any of these two, depending upon convenience.  The lines of the inclined letters are drawn at an approximate inclination of 75O to the right.
  • Double Stroke Letters. The thickness of the lines of the double-stroke letters cannot be obtained by a single stroke of pencil and hence, two strokes of the pencil are used.  This is the reason why these are called double stroke letters. The letters and numerals have uniform thickness in this style. The ratio of thickness and height of letters is 1:10 and 1: 14.

A good style of single stroke lettering should aim at:

  • Uniformity of Thickness. Conical point pencil is used for uniformity. Pencil should not be too sharp as it would pierce into the surface of the drawing paper.
  • Uniformity of Size. The width of the stroke of the pencil or pen is to be same as the width of the letter. Light guide lines for both top and bottom of letters should always be drawn with a sharp pencil.
  • Uniformity of Style. One of the two styles, vertical or inclined, should be used. Vertical lettering is usually preferred. Both vertical and inclined letters are standard and the technicians should use them according to their practice and convenience.
  • Uniformity of Spacing. Uniformity in spacing of letters, whether they are vertical or inclined, is a matter of equalizing the spaces between alphabets, words, lines, etc. The background area between letters, not only the distance between them, should be approximately equal.
  • Uniformity of Shape. The shape of all the letters, irrespective of the styles or types used, should be uniform. If inclined letters are used, all of them must have the same inclination and should be inclined towards the right-hand side.
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