UNIT OF DIMENSION AND GENERAL RULE FOR DIMENSIONING

UNIT OF DIMENSION:

          As far as possible all dimensions should be given in millimeters, omitting the abbreviation mm. Even when it is not convenient to give dimension in millimeters and another unit is used, only the dimension figures are written. But a foot note such as "All dimensions are present in centimeters/meters" is inserted in a prominent place near the title block. The decimal point in a dimension should be quite distinct and written in line with dimension line. A zero must always precedes the decimal point when the dimension is less than unity.

GENERAL RULE FOR DIMENSIONING:

1) Every dimension of a part/segment must be given, but none should be given more than once.

2) Every dimension should be given so completely that further calculation or assumption of any dimension, or direct measurement from the drawing is not necessary.

3) A dimension should be placed on the view where it use is shown more clearly.

4) Dimension should be placed outside the views, unless they are clearer and more easily read inside.

5) Dimensioning between hidden lines and mutual crossing of dimension lines should be avoided. 

6) Dimension lines should not cross any other line of the drawing.

7) An outline or centre line should never be used as a dimension line. A centre line may be extended to serve as an extension line.

8) In general we use two types of dimensional systems (i.e, Unidirectional and aligned), in those Aligned dimensioning system is recommended.