information. Dimensions should be selected to suitthe function and should not be subject to morethan one interpretation.Detailed dimensioning format and standardswill be discussed freely in this chapter to meetspecific requirements. You will notice that dimen-sioning construction or project drawings differsin some applications from dimensioning generaltechnical drawings. This occurs primarily becauseof the materials and methods of construction.Units of MeasureAs we stated earlier, the unit of measurementselected should be according to the policy of theuser and the geographical area in which theproject plans will be used. The U.S. linear unitcommonly used on project drawings is the inch,while that of SI (metric) linear units is themillimeter. On drawings where all dimensions areeither in millimeters or inches, individual linearunit identification is NOT required. However,when this is the case, your drawing shouldcontain a note stating “UNLESS OTHERWISESPECIFIED, ALL DIMENSIONS ARE ININCHES” (or“IN MILLIMETERS,” asapplicable). Millimeter dimension values shownon an inch-dimensioned drawing must be followedby the symbol mm, while inch dimension valuesshown on a millimeter-dimensioned drawing willbe followed by the abbreviation IN.Similarly, dimensions for angular units areexpressed in either degrees and decimal parts ofa degree or in degrees, minutes, and seconds.Refer to figure 10-3 for guidance, as applicable.Figure 10-3.-Dimensioning angular units.Application of DimensionsDimensions are applied by means of dimensionlines, extension lines, or a leader from a dimen-sion, note, or specification directed to theappropriate feature. Some of the standard rulesto be followed when you are drawing DIMEN-SION LINES are as follows:1. The breaking of dimension lines forinsertion of numerals, as shown in figure 10-4,Figure 10-4.-Applications of dimensions and dimensionlines: A. Breaking dimension lines for insertion ofnumerals; B. Grouping lines for uniform appearance;C. Proper spacing of dimension lines from object.10-7
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