Engineering drawing is a universal language of communication between a Designer, Manufacturer and Inspector, it describes the shape, size and Specification of components to be manufactured.
Shape of component is described by different types of Orthographic views, Detail views, and Sectional view.
Size and location of features of a component is described by dimensions derived from different views on drawing sheet.
And necessary specifications required to produce the component are listed as notes in drawing sheet.
ISO 129-1:2018 and ASME 14.5-2018 defines the standards of Dimensioning system.
Different types of dimension which describes the size of component are:
Linear dimension: it describes the straight line distance between two points which may aligned, horizontal, vertical and inclined to each other.
Angular Dimension: it describe the angle between two lines or surfaces.
Radial Dimension: it describes the radius of circle or arc.
Diameter Dimension: It describes the diameter of circular and cylindrical feature. i.e. holes and shaft.
Arc Length: it describes the length of curved feature or arc.
Methods of Dimensioning:
Chain dimensioning: Dimensions are derived from one features to its adjacent feature in a series.
Tolerance accumulation (stack-up) is main dis advantage of this type of dimensioning method.
Base line/Parallel Dimensioning: All dimensions are derived from a common point, line, or a datum.
No tolerance accumulation is seen in this type of dimensioning method but it creates more dimensional lines.
Combined dimensioning: It is combination of both chain and base line dimensioning methods.
Coordinate dimensioning: The locations of the features are described in X and Y coordinates relative to a fixed origin.
Tabular Dimensioning: Dimension and location of features are provided on a tabular column not directly on the drawing.
Ordinate dimensioning: The location of features are measured in X or Y axis, from origin usually from bottom left corner using only one dimension line from origin.
This system is used to generate turning drawing of long shafts.
Running or Progressive Dimensioning: All dimensions are measured from single reference point, and values increase progressively along the object.
