Saturday, June 21, 2014

Scales in Engineering Drawing (Mechanical Department @ LAQSHYA College)

Engineering Drawing - Scales
Dimensions of large objects must be reduced to accommodate on standard size drawing sheet. This reduction creates a scale of that reduction ratio, which is generally a fraction. Such a scale is called reducing scale and that ratio is called representative factor.
Similarly in case of tiny objects dimensions must be increased for above purpose. Hence this scale is called enlarging scale.
Here the ratio called representative factor is more than unity.

Representative factor (r.f.) =   Dimension of drawing / Dimension of object

Length of scale =     r.f.  * max. Length to be measured.

Types of scales:

  1. Plain scales                 ( for dimensions up to single decimal)
  2. Diagonal scales           ( for dimensions up to two decimals)
  3. Vernier scales             ( for dimensions up to two decimals)
  4. Comparative scales     ( for comparing two different units)
  5. Scale of cords              ( for measuring/constructing angles)
Plain scale
Plain scale: - This type of scale represents two units or a unit and its sub-division.

Problem:-  Draw a scale 1 cm = 1m to read decimeters, to measure maximum distance of 6 m. Show on it a distance of 4 m and 6 dm.


Calculate r.f. = Dimension of drawing / Dimension of object
                                   r.f. = 1cm/ 1m = 1/100
 length of scale =   r.f. x max. Distance
                       = 1/100 x 600 cm
                                  = 6 cms
B) Draw a line 6 cm long and divide it in 6 equal parts. Each part will represent larger division unit.
C) Sub divides the first part which will represent second unit or fraction of first unit.
D) Place (0) at the end of first unit. Number the units on right side of zero and subdivisions. On left-hand side of zero. Take height of scale 5 to 10 mm for getting a look of scale.
E) After construction of scale mention its rf and name of scale as shown.
 f) Show the distance 4 m 6 dm on it as shown.

Article By
N.Nagendra Kumar                  
Assistant Professor
Mechanical Department
LAQSHYA Institute of Technology & Sciences              

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