Dimensioning is a method of accurately communicating size information about objects and structures so they can be produced. After completing this chapter you will be able to apply the standard dimensioning practices for mechanical drawings, differentiate current ANSI standards and past practices for dimensioning. | Dimensioning Definition Size and shape Position Surface texture or Geometric characteristic Of a feature A dimension is a numerical value that defines the: Units Millimeters (mm) in the metric system Inches in the English system The default dimensional units in most CAD systems are: NOTE: Dimensions in millimeters typically expressed as whole numbers Dimensions in inches typically expressed to two decimal place accuracy Terminology Leader – Line (w/ arrow) drawn from a feature to a note Reference dimension – Numerical value provided for information only and not used in fabrication of the part NOTE: Dimension text heights are typically 3 mm, and are uniform throughout the drawing Dimensioning Guidelines for Prisms-1 Do not repeat dimensions Dimension most descriptive view of feature being dimensioned Dimension between views Omit one intermediate dimension Smaller dimensions inside of larger dimensions Extension lines may cross object lines and other extension lines Dimensioning Guidelines for Prisms-2 Avoid dimensioning inside an object Dimension to visible object lines, not to hidden lines Dimensioning Rules/Guidelines for Cylinders and Arcs Dimension diameter of cylindrical parts in their rectangular views Dimension diameter of cylindrical holes in their circular views Dimension radius of fillets and rounds (180 degrees or less) Locate center of holes C’est . | Dimensioning Definition Size and shape Position Surface texture or Geometric characteristic Of a feature A dimension is a numerical value that defines the: Units Millimeters (mm) in the metric system Inches in the English system The default dimensional units in most CAD systems are: NOTE: Dimensions in millimeters typically expressed as whole numbers Dimensions in inches typically expressed to two decimal place accuracy Terminology Leader – Line (w/ arrow) drawn from a feature to a note Reference dimension – Numerical value provided for information only and not used in fabrication of the part NOTE: Dimension text heights are typically 3 mm, and are uniform throughout the drawing Dimensioning Guidelines for Prisms-1 Do not repeat dimensions Dimension most descriptive view of feature being dimensioned Dimension between views Omit one intermediate dimension Smaller dimensions inside of larger dimensions Extension lines may cross object lines and other extension lines Dimensioning Guidelines for Prisms-2 Avoid dimensioning inside an object Dimension to visible object lines, not to hidden lines Dimensioning Rules/Guidelines for Cylinders and Arcs Dimension diameter of cylindrical parts in their rectangular views Dimension diameter of cylindrical holes in their circular views Dimension radius of fillets and rounds (180 degrees or less) Locate center of holes C’est tout!
