Machine Drawing

(avery) #1
A4

A3

A2

A1

A0

10


PRINCIPLES OF DRAWING* 2


2.1 Introduction


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


and size of the object can be visualised 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).


2.2 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.


2.2.1 Sheet Sizes


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 m^2 , 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 (Fig. 2.1).


2.2.2 Designation of Sizes


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.


Fig. 2.1 Drawing sheet formats

*Material for this chapter has been taken from BIS; SP–46: 1988.

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