TYPES OF LINES

Lines of different types and thicknesses are used for graphical representation of objects. The

types of lines and their applications are shown in Table. Typical applications of different

types of lines are shown in Figs. 

THICKNESS OF LINES

Two thicknesses of lines are used in draughting practice. The ratio of the thick to thin line

should not be less than 2:1. The thickness of lines should be chosen according to the size and

type of the drawing from the following range:

0.18, 0.25, 0.35, 0.5, 0.7, 1, 1.4 and 2

It is recommended that the space between two parallel lines, including hatching, should

never be less than 0.7 mm.

SCALES IN DRAWING

 Scale is the ratio of the linear dimension of an element of an object as represented in the

drawing, to the real linear dimension of the same element of the object itself. Wherever possible,

it is desirable to make full size drawings, so as to represent true shapes and sizes. If this is not

practicable, the largest possible scale should be used. While drawing very small objects, such

as watch components and other similar objects, it is advisable to use enlarging scales.

DESIGNATION

The complete designation of a scale should consist of the word Scale, followed by the indication

of its ratio as:

SCALE 1 : 1 for full size,

SCALE × : 1 for enlarged scales,

SCALE 1 : × for reduced scales.

The designation of the scale used on the drawing should be shown in the title block.

RECMANDED SCALE

The recommended scales for use on technical drawings are given in Table . The scale and

the size of the object in turn, will decide the size of the drawing.

SCALE SPECIFICATION

If all drawings are made to the same scale, the scale should be indicated in or near the title

block. Where it is necessary to use more than one scale on a drawing, the main scale only

should be shown in the title block and all the other scales, adjacent to the item reference

number of the part concerned or near the drawings.

BORDER AND FRAMES

 Borders enclosed by the edges of the trimmed sheet and the frame, limiting the drawing space,

should be provided with all sheet sizes. It is recommended that these borders have a minimum

width of 20 mm for the sizes A0 and A1 and a minimum width of 10 mm for the sizes A2, A3

and A4 (Fig.). A filing margin for taking perforations, may be provided on the edge, far left

of the title block.

Centring Mark

Four centring marks may be provided, in order to facilitate positioning of the drawing when

reproduced or microfilmed. Two orientation marks may be provided to indicate the orientation

of the drawing sheet on the drawing board

METRIC REFERENCE GRADUATUON

It is recommended to provide a figure-less metric reference graduation, with a minimum length

of 100 mm and divided into 10 intervals on all the drawing sheets (Fig. ) which are intended

to be microfilmed. The metric reference graduation may be disposed symmetrically about a

centring mark, near the frame at the border, with a minimum width of 5 mm.

GRID REFERENCE SYSTEM

The provision of a grid reference system is recommended for all the sizes, in order to permit

easy location on the drawing of details, additions, modifications, etc. The number of divisions

should be divisible by two and be chosen in relation to the complexity of the drawing. It is

recommended that the length of any side of the grid should not be less than 25 mm and not

more than 75 mm. The rectangles of the grid should be referenced by means of capital letters

along one edge and numerals along the other edge, as shown in Fig. 2.4. The numbering direction

may start at the sheet corner opposite to the title block and be repeated on the opposite sides.

Trimming marks

Trimming marks may be provided in the borders at the four corners of the sheet, in order to

facilitate trimming. These marks may be in the form of right angled isosceles triangles or two

short strokes at each corner (Fig.).

TITLE BLOCK

 The title block should lie within the drawing

space such that, the location of it, containing the

identification of the drawing, is at the bottom

right hand corner. This must be followed, both

for sheets positioned horizontally or vertically

The direction of viewing of the title block

should correspond in general with that of the

drawing. The title block can have a maximum

length of 170 mm. Figure 2.3 shows a typical title

block, providing the following information:

(i) Title of the drawing

(ii) Sheet number

(iii) Scale

(iv) Symbol, denoting the method of projection

(v) Name of the firm

(vi) Initials of staff drawn, checked and approved.

NOTE :According to Bureau of Indian Standards, SP-46:1998, ‘‘Engineering Drawing Practice

for Schools and Colleges’’, First angle projection is preferred.

PRINCIPLE OF DRAWING

INTRODUCTION

 Engineering drawings are to be prepared on standard size drawing sheets. The correct shape

and size of the object can be visualized from the understanding of not only the views of it but

also from the various types of lines used, dimensions, notes, scale, etc. To provide the correct

information about the drawings to all the people concerned, the drawings must be prepared,

following certain standard practices, as recommended by Bureau of Indian Standards (BIS).

DRAWING SHEET

Engineering drawings are prepared on drawing sheets

of standard sizes. The use of standard size sheet, saves

paper and facilitates convenient storage of drawings.

The basic principles involved in arriving at the sizes

of drawing sheets are:

(a) X : Y = 1 : √ 2  , (b) XY = 1

where X and Y are the sides of the sheet. For a

reference size A0 (Table 2.1) having a surface area of

1 m2, X = 841 mm and Y = 1189 mm. The successive

format sizes are obtained either by halving along the

length or doubling along the width, the areas being

in the ratio 1:2 

DESIGNATION OF SIZE

The original drawing should be made on the smallest

sheet, permitting the necessary clarity and resolution.

The preferred sizes according to ISO-A series (First

choice) of the drawing sheets are given in Table 2.1.

When sheets of greater length are needed, special

elongated sizes (Second choice) are used (Table 2.2).

These sizes are obtained by extending the shorter

sides of format of the ISO-A series to lengths that are

multiples of the shorter sides of the chosen basic

format.