Dimensioning
The size and other details of the object essential for its construction and function, using lines, numerals, symbols, notes, etc are required to be indicated in a drawing by proper dimensioning. These dimensions indicated should be those that are essential for the production, inspection and functioning of the object and should be mistaken as those that are required to make the drawing of an object.  The dimensions are written either above the dimension lines or inserted at the middle by breaking the dimension lines.

Normally two types of dimensioning system exist. i.e. Aligned system and the unidirectional system.These are shown in figure 3.

In the aligned system the dimensions are placed perpendicular to the dimension line in such a way that it may be read from bottom edge or right hand edge of the drawing sheet. The horizontal and inclined dimension can be read from the bottom where as all the vertical dimensions can be read from the right hand side of the drawing sheet.
In the unidirectional system, the dimensions are so oriented such that they can be read from the bottom of the drawing.

Figure 3. The aligned system and unidirectional system of dimensioning.

 

Rules to be followed for dimensioning. Refer figure 4.

• Each feature is dimensioned and positioned only once.
• Each feature is dimensioned and positioned where its shape shows.
• Size dimensions – give the size of the component.
• Every solid has three dimensions, each of the geometric shapes making up the object must have its height, width, and depth indicated in the dimensioning.

 

Figure 4. typical dimension lines