182 Print Reading for Industry Copyright Goodheart-Willcox Co., Inc. eliminates numerous dimension and extension lines and improves the clarity of the drawing. Coordi- nate dimensioning without dimension lines is also called ordinate dimensioning, arrowless dimen- sioning, or datum dimensioning. This system of dimensioning is especially useful on drawings of parts that are to be machined on computer numeri- cally controlled (CNC) equipment. Coordinate dimensioning without dimension lines requires “zero” reference planes be established from which all values are given in the X and Y directions. Dual dimensioning is used on a drawing to show both inch and millimeter values for some or all of the dimensions. Some companies place the millimeter value above the dimension line and the inch value below the dimension line. Other companies use the bracket method and place the metric value in brackets following the inch value, as shown in Figure 9-18. In either case, the method used should be consistent throughout the drawing. A note should appear on the print to explain the method used. Notes and Special Features Notes are almost always necessary to comple- ment views and dimensions. Local notes use leader lines to point to special features, holes, and threads. Special features often include machining speci- fications, including counterbores, countersinks, tapers, knurls, keyways, and chamfers. General notes usually apply to the entire part. Examples of general notes include FILLETS AND ROUNDS R.125 UNLESS SPECIFIED, FINISH ALL OVER, and BREAK ALL SHARP CORNERS. Many of these special fea- tures, machining specifications, and other notes are examined in more detail in Unit 11, Machining Specifications and Drawing Notes. Digital Product Definition The ASME Y14.41 Digital Product Definition Data Practices standard was developed to address alter- native practices for describing size and applying dimensions. Within these practices, an electronic model of the part or assembly can serve as the “contract” information, and the use of projected orthographic views is not required. Still included with the model file data are items you would expect to find on a standard drawing sheet, such as the title, approval dates, part number, originator’s name, and other pertinent data. Annotations, such as dimensions and notes, can also be included. However, rather than attaching the annotations to 2D views, they are attached to the 3D model on 2D planes, Figure 9-19. In reference books and standards, the annotations appear similar to how dimensioned pictorial drawings appear on paper. However, when displayed electronically, the dimen- sions rotate and turn with the model as the model is rotated. Because the 3D model provides much of the size description, annotations may only be necessary for critical measurements and tolerances, features that are not modeled (such as thread notes), or geo- metric size tolerances and datum identification. The Y14.41 standard also allows for a drawing graphic sheet to be included. The drawing graphic sheet may include orthographic and axonometric (rotated) views that are generated directly from the Goodheart-Willcox Publisher Figure 9-17. Coordinate dimensioning without dimension lines eliminates numerous dimension and extension lines and improves the clarity of the drawing. 3.000 2.250 1.500 .750 .000 .000 .500 1.500 1.750 2.000 2.250 2.500 2.750 3.000 3.250 3.500 4.500 5.000 R.250TYP 13X .250 Goodheart-Willcox Publisher Figure 9-18. Dual dimensioning is used on a drawing to show both inch and millimeter values. 2.500 [ 63.50 ] 1.125 [ 28.50 ]