DIMENSIONS

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What is Dimensioning
    
       A drawing describes the shape and size of a machine part and also furnishes details regarding the material, manufacturing processes, surface finish, and any other instructions required for the final assembly. The shape description of the part is made by drawing its orthographic views with the necessary sections. The size description of the part is made by furnishing details such as the distance between the two surfaces, location of holes, machining operations like drilling and tapping with their sizes, materials, number required, and etc. supply of these details on the drawing for the correct function of the part using lines, figures, symbols, notes, etc, is called dimensioning.  

       It should be noted that the dimensions shown on a drawing of a machine part should be those that are essential for its production, inspection and correct functioning in the final assembly and should not be misunderstood as those that required to make the drawing of the abject.

Lines and symbols

    The dimensions of a machine part are shown on the drawing using dimension lines, extension lines, leaders, arrowheads, symbols, figures, notes etc.illustrates dimensioning terms and notations.
   Lines of different types and thicknesses are used for graphical representation of objects.  The types of lines and their applications are Typical applications of different types of lines 

Dimension lines

     A dimension line is continuous thin line shown by arrowheads, drawn parallel to the line or surface whose measurement should be indicated. Generally the dimension lines should be placed outside the views wherever possible however some times they may be placed within the view, unless the drawing becomes very clear by doing so. For example dimension line which indicates 5.2 mm is placed within the view. The dimension lines should be placed at least 8mm away from the outline and all other parallel dimension lines should be placed at least 6mm apart and more if space per mints irrespective of the scale of the drawing. For example in the top view in fig. 5.2 the distance between the outline and the first dimension line showing 55mm and 17.5mm is 8mm and the distance between this dimension line and the second parallel dimension line showing 90mm is 6mm. note that the distance 8mm and 6mm are shown in the actual sizes and not according to the scale of the drawing. 

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