Rules for Dimensioning a Technical Drawing

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					                 Rules for Dimensioning a Technical Drawing

1.    Each dimension should be given clearly, so that it can be interpreted in only one
      way.

2.    Dimensions should not be duplicated, or the same information given in two
      different ways, and no dimensions should be given except those needed to
      produce or inspect the part.

3.    Dimensions should be given between views whenever possible. However, it is
      sometimes necessary to place a dimension above or below a view.

4.    Dimensions should be given so that it will not be necessary for the machinist to
      calculate, scale, or estimate any dimension.

5.    Dimensions should be attached to the view where the shape is best shown. This
      is most frequently the front view.

6.    Dimensions should be placed in the views where features dimensioned are
      shown true shape. This sometimes means dimensioning an auxiliary view.

7.    Avoid dimensioning to hidden lines wherever possible.

8.    Dimensions should not be placed upon a view unless clearness is promoted, and
      long extension lines are avoided.

9.    Dimensions applying to two adjacent views should be placed between views,
      unless clearness will be promoted by placing them outside the view.

10.   The longer dimensions should be placed outside all intermediate or shorter
      dimensions, so that dimension lines will not cross extension lines.

11.   In machine drawings, omit all inch marks, except when necessary for clearness;
      for example, 1” VALVE.

12.   A dimension should be attached to only one view: extension lines should not
      connect two views.

13.   Detail dimensions should “line up” in chain fashion.

14.   Avoid a complete chain of detail dimensions; better to omit one. Otherwise, add
      REF (reference) to one detail dimension, or to the overall dimension.

15.   Dimension lines should be spaced uniformly throughout the drawing. They
      should be spaced at least 3/8” from the object, and 1/4" apart.

16.   No line of the drawing should be used as a dimension line or coincide with a
      dimension line.

17.   Dimension line should never cross other dimension lines.
18.   Dimension lines should not cross extension lines; extension lines may cross each
      other.

19.   When extension lines cross other extension lines, no break should be made in
      either line.

20.   A center line may be extended and used as an extension line, in which case, it is
      still drawn as a center line.

21.   Center lines should not extend from view to view.

22.   Leaders for notes should be straight, not curved, and pointing to the circular
      views of holes whenever possible.

23.   Leaders should slope at 45, 30, or 60 degrees with horizontal text, but may be
      made at any angle except vertical or horizontal.

24.   Dimension figures should be approximately centered between the arrowheads,
      except that in a “stack” of dimensions, the figures should be “staggered”.

25.   Dimension figures should be 1/8” high for whole numbers, and 1/4" high for
      fractions.

26.   Notes should always be lettered horizontally on the drawing.

27.   Extension lines should not touch object lines, and should extend roughly 1/8”
      beyond dimension lines.

28.   In general, a cylinder is dimensioned by its diameter, an arc is dimensioned by its
      radius.

29.   A diameter dimension figure should be followed by DIA except when it is
      obviously a diameter.

30.   The letter R should always follow a radius dimension figure. The radial
      dimension line should have only one arrowhead, and it should touch the arc.