Scales

There is a wide variation in sizes for engineering objects. Some are very large (eg. Aero planes, rockets, etc) Some are vey small ( wrist watch, MEMs components)
There is a need to reduce or enlarge while drawing the objects on paper. Some objects can be drawn to their actual size. The proportion by which the drawing of aan object is enlarged or reduced is called the scale of the drawing.

Definition
A scale is defined as the ratio of the linear dimensions of the object as  represented in a drawing to the actual dimensions of the same.

• Drawings drawn with the same size as the objects are called full sized drawing.
• It is not convenient, always, to draw drawings of the object to its actual size. e.g. Buildings,
• Heavy machines, Bridges, Watches, Electronic devices etc.
• Hence scales are used to prepare drawing at

• Full size
• Reduced size 
• Enlarged size

BIS Recommended Scales are shown in table 1.

Table 1. The common scales recommended.

Intermediate scales can be used in exceptional cases where recommended scales can not be applied for functional reasons.

Types of Scale :-
Engineers Scale :  The relation between the dimension on the drawing and the actual dimension of the object is mentioned numerically  (like 10 mm = 15 m).

Graphical Scale:  Scale is drawn on the drawing itself. This takes care of the shrinkage of the engineer’s scale when the drawing becomes old.