DIMENSIONING CHAPTER TEN OBJECTIVES 1 Use conventional dimensioning

DIMENSIONING CHAPTER TEN

OBJECTIVES 1. Use conventional dimensioning techniques to describe size and shape accurately on an engineering drawing. 2. Create and read a drawing at a specified scale. 3. Correctly place dimension lines, extension lines, angles, and notes. 4. Dimension circles, arcs, and inclined surfaces. 5. Apply finish symbols and notes to a drawing. 6. Dimension contours. 7. Use standard practices for dimensioning prisms, cylinders, holes, and curves. 8. List practices for dimensioning a solid model as documentation. 9. Identify guidelines for the dos and don’ts of dimensioning. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 2 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

UNDERSTANDING DIMENSIONING The increasing need for precision manufacturing and interchangeability has shifted responsibility for size control to the design engineer or detail drafter. Practices for dimensioning architectural and structural drawings are similar in many ways to those for dimensioning manufactured parts, but some practices differ. Refer to the following standards: • ANSI/ASME Y 14. 5 -2009 Dimensioning and Tolerancing • ASME Y 14. 41 -2003 Digital Product definition Data Practices • ASME B 4. 2 -1978 (R 1999) Preferred Metric Limits and Fits Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 3 Automatically Generated Dimensions. Views and dimensions can be generated automatically from a solid model. (Courtesy of Robert Kincaid. ) © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

Three Aspects of Good Dimensioning Technique of dimensioning Placement of dimensions Choice of dimensions Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 4 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

Tolerance is the total amount that the feature on the actual part is allowed to vary from what is specified by the drawing or model dimension. E X A M P L E S ALL TOLERANCES ±. 02 INCH UNLESS OTHERWISE NOTED. A Title Block Specifying Tolerances. (Courtesy of Dynojet Research, Inc. ) Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 5 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

Geometric Breakdown Engineering structures are composed largely of simple geometric shapes, such as the prism, cylinder, pyramid, cone, and sphere. They may be exterior (positive) or interior (negative) forms. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 6 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

LINES USED IN DIMENSIONING Dimension, Extension and Centerlines Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 7 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

Guidelines for USING DIMENSION AND EXTENSION LINES Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 8 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

ARROWHEADS When you are drawing by hand using the arrowhead method in which both strokes are directed toward the point, it is easier to make the strokes toward yourself. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 9 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

LEADERS A leader is a thin, solid line directing attention to a note or dimension and starting with an arrowhead or dot. For the Best Appearance, Make Leaders • near each other and parallel • across as few lines as possible Don’t Make Leaders • parallel to nearby lines of the drawing • through a corner of the view • across each other • longer than needed • horizontal or vertical Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 10 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DRAWING SCALE AND DIMENSIONING Drawing scale is noted in the title block. The drawing should not be scaled for dimensions. (Courtesy of Dynojet Research, Inc. ) Many standard title blocks include a note such as: DO NOT SCALE DRAWING FOR DIMENSIONS Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 11 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIRECTION OF DIMENSION VALUES AND NOTES All dimension values and notes are lettered horizontally to be read from the bottom of the sheet, as oriented by the title block. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 12 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSION UNITS A note stating ALL MEASUREMENTS IN MILLIMETERS or ALL MEASUREMENTS IN INCHES UNLESS OTHERWISE NOTED is used in the title block to indicate the measurement units… (Courtesy of Dynojet Research, Inc. ) Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 13 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

MILLIMETER VALUES The millimeter is the commonly used unit for most metric engineering drawings. Oneplace millimeter decimals are used when tolerance limits permit. Two (or more)–place millimeter decimals are used when higher tolerances are required. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 14 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DECIMAL-INCH VALUES Two-place inch decimals are typical when tolerance limits permit. Three or more decimal places are used for tolerance limits in the thousandths of an inch. In two-place decimals, the second place preferably should be an even digit. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 15 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

RULES FOR DIMENSION VALUES Good hand-lettering is important for dimension values on sketches. The shop produces according to the directions on the drawing so to save time and prevent costly mistakes, make all lettering perfectly legible. Make all decimal points bold, allowing ample space. When the metric dimension is a whole number, do not show either a decimal point or a zero. When the metric dimension is less than 1 mm, a zero precedes the decimal point. When the decimal-inch dimension is used on drawings, a zero is not used before the decimal point of values less than 1 in. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 16 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DUAL DIMENSIONING and COMBINATION UNITS Dual dimensioning is used to show metric and decimal-inch dimensions on the same drawing. Two methods of displaying the dual dimensions are: 1. 2. Position Method Bracket Method Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman DIMENSIONS IN () ARE MILLIMETERS 17 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSION SYMBOLS Dimensioning symbols are used to replace traditional terms or abbreviations. Form and Proportion of Dimensioning Symbols. (Reprinted from ASME Y 14. 5 M-1994 (R 2004), by permission of The American Society of Mechanical Engineers. All rights reserved. ) Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 18 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

PLACING AND SHOWING DIMENSIONS LEGIBLY Rules for the placement of dimensions help you dimension your drawings so that they are clear and readable… Fitting Dimension Values in Limited Spaces (Metric Dimensions) Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 19 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

PLACING AND SHOWING DIMENSIONS LEGIBLY continued… Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 20 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

SUPERFLUOUS DIMENSIONS All necessary dimensions must be shown, but do not give unnecessary or superfluous dimensions. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 21 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

SUPERFLUOUS DIMENSIONS continued… No unnecessary or superfluous dimensions. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 22 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSIONING ANGLES Angles are dimensioned by specifying the angle in degrees and a linear dimension. The coordinate method is better when a high degree of accuracy is required Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 23 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSIONING ARCS, FILLETS AND ROUNDS A circular arc is dimensioned in the view where its true shape in seen by giving the value for its radius preceded by the abbreviation R. Individual fillets and rounds are dimensioned like other arcs. FILLETS R 6 AND ROUNDS R 3 UNLESS OTHERWISE SPECIFIED or ALL CASTING RADII R 6 UNLESS NOTED or simply ALL FILLETS AND ROUNDS R 6. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 24 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

SIZE DIMENSIONS: CYLINDERS Cylinders are usually dimensioned by giving the diameter and length where the cylinder appears as a rectangle. Use “Ø” to indicate circular shape Dimensioning a Machine Part Composed of Cylindrical Shapes Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 25 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

SIZE DIMENSIONING HOLES The leader of a note should point to the circular view of the hole, if possible. Countersunk, counterbored, spotfaced and tapped holes are usually specified by standard symbols or abbreviations. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 26 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSIONING COUNTERBORES AND SPOTFACES WITH FILLETS When a fillet radius is specified for a spotface dimension, the fillet radius is added to the outside of the spotface diameter, Counterbored hole with a fillet radius specified. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 27 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSIONING CURVES One way to dimension curves is to give a group of radii. Both circular and noncircular curves may be dimensioned by using coordinate dimensions, or datums. When angular measurements are unsatisfactory, you may give chordal dimensions Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 28 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSIONING ROUNDED-END SHAPES For accuracy, in parts d –g, overall lengths of rounded-end shapes are given, and radii are indicated, but without specific values. The center-to-center distance may be required for accurate location of some holes. In part g, the hole location is more critical than the location of the radius, so the two are located. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 29 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSIONING THREADS Local notes are used to specify dimensions of threads. For tapped holes, the notes should, if possible, be attached to the circular views of the holes. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 30 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSIONING TAPERS A taper is a conical surface on a shaft or in a hole. The usual method of dimensioning a taper is to give the amount of taper in a note, such as TAPER 0. 167 ON DIA (with TO GAGE often added), and then give the diameter at one end with the length or give the diameter at both ends and omit the length. Taper on diameter means the difference in diameter per unit of length. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 31 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSIONING CHAMFERS Achamfer is a beveled or sloping edge. It is dimensioned by giving the length of the offset and the angle, as in Figure 10. 51 a. A 45° chamfer also may be dimensioned Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 32 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSIONING KEYWAYS The preferred method of dimensioning the depth of a keyway is to give the dimension from the bottom of the keyway to the opposite side of the shaft or hole. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 33 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

DIMENSIONING KNURLS A knurl is a roughened surface to provide a better handgrip or to be used for a press fit between two parts. For handgrip purposes, it is necessary only to give the pitch of the knurl, the type of knurling, and the length of the knurled area. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 34 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

FINISH MARKS A finish mark is used to indicate that a surface is to be machined, or finished, as on a rough casting or forging. To the patternmaker or diemaker, a finish mark means that allowance of extra metal in the rough workpiece must be provided for the machining. The finish mark is shown only on the edge view of a finished surface and is repeated in any other view in which the surface appears as a line, even if the line is a hidden line. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 35 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 36 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

SURFACE ROUGHNESS Surface finish is intimately related to the functioning of a surface, and proper specification of finish of surfaces such as bearings and seals is necessary. Surface quality specifications should be used only where needed, since the cost of producing a finished surface becomes greater as the quality of the surface called for is increased. Generally, the ideal surface finish is the roughest that will do the job satisfactorily. Surface Texture Symbols and Construction. (Reprinted from ASME Y 14. 36 M-1996 (R 2002), by permission of The American Society of Mechanical Engineers. All rights reserved. ) Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 37 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

LOCATION DIMENSIONS After you have specified the sizes of the geometric shapes composing the structure, give location dimensions to show the relative positions of these geometric shapes. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 38 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

MATING DIMENSIONS Mating dimensions should be given on the multiview drawings in the corresponding locations. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 39 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

TABULAR DIMENSIONS A series of objects having like features but varying in dimensions may be represented by one drawing. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 40 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

COORDINATE DIMENSIONING A set of three mutually perpendicular datum or reference planes is usually required for coordinate dimensioning. These planes either must be obvious. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 41 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

SHEET METAL BENDS In sheet metal dimensioning, allowance must be made for bends. The intersection of the plane surfaces adjacent to a bend is called the mold line, and this line, rather than the center of the arc, is used to determine dimensions. Bends Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 42 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.

NOTES It is usually necessary to supplement the direct dimensions with notes. Notes should be brief and carefully worded to allow only one interpretation. Notes should always be lettered horizontally on the sheet and arranged systematically. They should not be crowded and should not be placed between views, if possible. Notes are classified as general notes when they apply to an entire drawing and as local notes when they apply to specific items. Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman 43 © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. • All Rights Reserved.