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Metric Dimensioning Guide

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Revision as of 02:49, 24 March 2006; view current revision
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Written by Allan

Created 2-July-2004

Lines

  • Projection lines indicate extremities of a dimension. A gap of 1mm is generally drawn from the object to the start of the projection line. An extension of 2mm is generally drawn past the dimension line.
  • Dimension lines run between the projection lines. They generally terminate with and arrowhead or tick. Arrowheads are usually 3x1mm and ticks, 2mm long.
  • Thin linework should be used of dimension and projection lines.
  • For dimensions that cannot be drawn to there true termination point, the free end is terminated in a double arrowhead.
  • 15 x scale is the formula for working out the gap between dimension lines and the object.

Notation

  • Dimensions are usually in millimetres (millimeters). Place a note in the title block stating "ALL DIMENSIONS IN mm" to avoid the need to specify "mm" after every number.
  • Dimensions lest than 1 should lead with a "0" before the decimal point. Example: 0.5
  • Angular dimesions are specified in decimal degrees, degrees and minutes or degrees minutes and seconds. Example: 10.5° - 10°30' - 10°30'30"
  • When specifying an overall dimension, one non-critical component dimension should be omitted. Where all component dimesions must be specified, and overall lenght should be specified as an auxiliary dimension.
  • Auxiliary dimensions should be shown in brackets or noted "REFERENCE".
  • Dimensions that are not to scale are underlined or noted "NTS".
  • Where the "plus minus" symbol appears after a number, the number has been rounded of to the nearest whole number. Generally this is not required, unless in clears up why a dimension string does not close off.

Alignment

  • There are two common methods of aligning notations, "Aligned" is the most common.
  1. Aligned: The dimensions are parallel to the dimension line. Dimensions can always be readable either from the bottom or the right of the drawing.
  2. Unidirectional: All dimensions are written horizontally.

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