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## CHAPTER 10

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**CHAPTER 10**Dimensioning and Tolerancing**Learning Objectives**• Identify and use common dimensioning systems • Explain and apply dimensioning standards based on ASME Y14.5-2009 • Apply proper specific notes for manufacturing features • Place proper general notes and flag notes on a drawing • Interpret and use correct tolerancing techniques**Learning Objectives**• Prepare completely dimensioned multiview drawings from engineering sketches and industrial drawings • Apply draft angles as needed to a drawing • Dimension CAD/CAM machine tool drawings • Prepare casting and forging drawings**Learning Objectives**• Provide surface finish symbols on drawings • Solve tolerance problems including limits and fits • Use an engineering problem as the basis for your layout techniques • Describe the purpose of ISO 9000 Quality Systems Standard and related standards**Dimensions**• Required on detail drawings • Provide shape and size description • Size dimensions • Location dimensions • Notes • Local notes (specific notes) • General notes**ASME Dimensioning Standards**• ASME Y14.5, Dimensioning and Tolerancing • General note: DIMENSIONING AND TOLERANCING PER ASME Y14.5-2009 • Several other ASME documents with standards related to dimensioning and tolerancing**Dimensioning Definitions**• Actual size • Allowance • Basic dimension • Bilateral tolerance • Datum • Diameter • Feature • Feature of size • Geometric tolerance • Least material condition (LMC) • Limits of dimension**Dimensioning Definitions**• Maximum material condition (MMC) • Nominal size • Radius • Reference dimension • Stock size • Specified dimension • Tolerance • Unilateral tolerance**Fundamental ASME Y14.5 Dimensioning Rules**• Each dimension has a tolerance except reference, maximum, minimum, or stock • Dimensioning and tolerancing must be complete • Show each necessary dimension of an end product • Select and arrange dimensions to suit the function and mating relationship of a part**Fundamental ASME Y14.5 Dimensioning Rules**• Dimensions must not be subject to more than one interpretation • Do not specify the manufacturing processes unless necessary • Identify nonmandatory dimensions with an appropriate note • Arrange dimensions to provide required information and optimum readability • Show dimensions in true profile views and visible outlines**Fundamental ASME Y14.5 Dimensioning Rules**• Dimension diameter or thickness of materials manufactured to gage or code numbers • 90°angle is implied for centerlines and lines • 90°basic angle is implied for centerlines located by basic dimensions • A zero basic dimension applies where axes, center planes, or surfaces are shown one over the other with established geometric controls**Fundamental ASME Y14.5 Dimensioning Rules**• Unless otherwise specified, all: • Dimensions and tolerances are measured at 20°C (68°F) • Dimensions and tolerances apply in a free state condition except for nonrigid parts • Tolerances apply for the full depth, length, and width of the feature • Dimensions and tolerances apply on the drawing where specified**Fundamental ASME Y14.5 Dimensioning Rules**• Coordinate systems: • Right-handed (arranged clockwise) • Labeled axes and positive direction shown • 3-D model complies with ASME Y14.41, Digital Product Definition Data Practices**Unidirectional Dimensioning**• Numerals, figures, and notes lettered horizontally • Read from the bottom of the drawing sheet • Mechanical drafting for manufacturing**Aligned Dimensioning**• Numerals, figures, and notes aligned with the dimension lines • Horizontal dimensions read from the bottom • Vertical dimensions read from the right side • Architectural and structural drafting 0**Rectangular Coordinate Dimensioning without Dimension Lines**• Ordinate dimensioning • Dimension values aligned with extension lines • Dimension represents a measurement originating from datums or coordinates • Features such as holes sized using specific notes or a table • Popular for: • Precision sheet metal part drawings • Electronics drafting**Tabular Dimensioning**• Form of rectangular coordinate dimensioning without dimension lines • Features dimensioned in a table**Chart Dimensioning**• Used when a part or assembly has one or more dimensions that change depending on the specific application**Millimeter Dimensions**• Millimeters (mm) • Common International System of Units (SI) unit of measure • General note: UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN MILLIMETERS • Follow any inch dimensions with IN**Proper Use of Metric Units**• Omit decimal point and 0 when dimension is a whole number • Precede a decimal value that is less than 1 with a 0 • When the value is greater than a whole number by a fraction of a mm, do not place a 0 next to last digit • Exception: when displaying tolerance values**Proper Use of Metric Units**• Plus and minus tolerance values have same number of decimal places • Limit tolerance values have same number of decimal points • Unilateral tolerances use a single 0 without a corresponding + or – sign**Inch Dimensions**• Decimal inches (IN) • United States (U.S.) customary unit of measure • General note: UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN INCHES • Follow any millimeter dimensions with mm**Proper Use of Inch Units**• Do not precede a value that is less than 1 inch with a 0 • Express a specified dimension to the same number of decimal places as its tolerance • Fractional inches generally indicate larger tolerance**Proper Use of Inch Units**• Plus and minus tolerance values have the same number of decimal places • Unilateral tolerances use the + and – sign • The 0 value has the same number of decimal places as the value that is greater or less than 0 • Limit tolerance values have the same number of decimal points**Proper Use of Angular Units**• Use decimal or degrees–minutes–seconds format • Angle and tolerance values have the same number of decimal places • Include 0°or 0°0″ when specifying only minutes or seconds, as applicable**Using Fractions**• Not as common as decimal inches or millimeters • Architectural and structural drawings • Generally indicate larger tolerance**Arrowheads**• Terminate dimension lines and leaders • Three times as long as they are wide • Consistent size • Filled in solid or open**Dimension Line Spacing**• First dimension line: • Uniform distance from the object • .375 in. (10 mm) minimum • .5 - 1.0 in. (12 - 24 mm) preferred • Succeeding dimension lines: • Equally spaced • .25 in. (6 mm) minimum • .5 - .75 in. (12 - 20 mm) preferred**Chain Dimensioning**• Creates tolerance stacking (tolerance buildup) • Omit one intermediate dimension or the overall dimension**Baseline Dimensioning**• Size or location of features controlled from a common reference plane • Reduces possibility of tolerance stacking**Direct Dimensioning**• Results in the least tolerance stacking**Preferred Dimensioning Practices**• Avoid crossing extension lines • Do not break extension lines when they cross • Never cross extension lines over dimension lines • Break the extension line where it crosses over a dimension line when necessary**Preferred Dimensioning Practices**• Never break a dimension line • Break extension lines when they cross over or near an arrowhead • Avoid dimensioning over or through the object • Avoid dimensioning to hidden features**Preferred Dimensioning Practices**• Avoid long extension lines • Avoid using any line of the object as an extension line • Dimension between views when possible • Group adjacent dimensions**Preferred Dimensioning Practices**• Dimension to views that provide the best shape description • Do not use a centerline, extension line, phantom line, visible object line, or a continuation of any of these lines as a dimension line • Stagger adjacent dimension numerals so they do not line up**Dimensioning Hexagons and Other Polygons**• Dimension across the flats**Additional Radius Dimensioning Applications**• True radius • TRUE R followed by the actual radius • Controlled radius • CR followed by the radius • Spherical radius • SR followed by the radius