Presentation on theme: "Dimensioning and Tolerancing"— Presentation transcript:
1Dimensioning and Tolerancing CHAPTER 10Dimensioning and Tolerancing
2Learning Objectives Identify and use common dimensioning systems Explain and apply dimensioning standards based on ASME YApply proper specific notes for manufacturing featuresPlace proper general notes and flag notes on a drawingInterpret and use correct tolerancing techniques
3Learning ObjectivesPrepare completely dimensioned multiview drawings from engineering sketches and industrial drawingsApply draft angles as needed to a drawingDimension CAD/CAM machine tool drawingsPrepare casting and forging drawings
4Learning Objectives Provide surface finish symbols on drawings Solve tolerance problems including limits and fitsUse an engineering problem as the basis for your layout techniquesDescribe the purpose of ISO 9000 Quality Systems Standard and related standards
5Dimensions Required on detail drawings Provide shape and size descriptionSize dimensionsLocation dimensionsNotesLocal notes (specific notes)General notes
7ASME Dimensioning Standards ASME Y14.5, Dimensioning and TolerancingGeneral note: DIMENSIONING AND TOLERANCING PER ASME YSeveral other ASME documents with standards related to dimensioning and tolerancing
8Dimensioning Definitions Actual sizeFeature of sizeAllowanceGeometric toleranceBasic dimensionLeast material condition (LMC)Bilateral toleranceDatumLimits of dimensionDiameterFeature
9Dimensioning Definitions Maximum material condition (MMC)Specified dimensionNominal sizeToleranceRadiusUnilateral toleranceReference dimensionStock size
10Fundamental ASME Y14.5 Dimensioning Rules Each dimension has a tolerance except reference, maximum, minimum, or stockDimensioning and tolerancing must be completeShow each necessary dimension of an end productSelect and arrange dimensions to suit the function and mating relationship of a part
11Fundamental ASME Y14.5 Dimensioning Rules Dimensions must not be subject to more than one interpretationDo not specify the manufacturing processes unless necessaryIdentify nonmandatory dimensions with an appropriate noteArrange dimensions to provide required information and optimum readabilityShow dimensions in true profile views and visible outlines
12Fundamental ASME Y14.5 Dimensioning Rules Dimension diameter or thickness of materials manufactured to gage or code numbers90°angle is implied for centerlines and lines90°basic angle is implied for centerlines located by basic dimensionsA zero basic dimension applies where axes, center planes, or surfaces are shown one over the other with established geometric controls
13Fundamental 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 partsTolerances apply for the full depth, length, and width of the featureDimensions and tolerances apply on the drawing where specified
14Fundamental ASME Y14.5 Dimensioning Rules Coordinate systems:Right-handed (arranged clockwise)Labeled axes and positive direction shown3-D model complies with ASME Y14.41, Digital Product Definition Data Practices
17Unidirectional Dimensioning Numerals, figures, and notes lettered horizontallyRead from the bottom of the drawing sheetMechanical drafting for manufacturing
18Aligned DimensioningNumerals, figures, and notes aligned with the dimension linesArchitectural and structural draftingHorizontal dimensions read from the bottomVertical dimensions read from the right side
19Rectangular Coordinate Dimensioning without Dimension Lines Dimension values aligned with extension linesDimension represents a measurement originating from datums or coordinatesFeatures such as holes sized using specific notes or a tablePopular for:Precision sheet metal part drawingsElectronics drafting
20Rectangular Coordinate Dimensioning without Dimension Lines
21Tabular DimensioningForm of rectangular coordinate dimensioning without dimension linesFeatures dimensioned in a table
22Chart DimensioningUsed when a part or assembly has one or more dimensions that change depending on the specific application
23Millimeter Dimensions Millimeters (mm)Common International System of Units (SI) unit of measureGeneral note: UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN MILLIMETERSFollow any inch dimensions with IN
24Proper Use of Metric Units Omit decimal point and 0 when dimension is a whole numberPrecede a decimal value that is less than 1 with a 0When the value is greater than a whole number by a fraction of a mm, do not place a 0 next to last digitException: when displaying tolerance values
25Proper Use of Metric Units Plus and minus tolerance values have same number of decimal placesLimit tolerance values have same number of decimal pointsUnilateral tolerances use a single 0 without a corresponding + or – sign
26Inch Dimensions Decimal inches (IN) United States (U.S.) customary unit of measureGeneral note: UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN INCHESFollow any millimeter dimensions with mm
27Proper Use of Inch Units Do not precede a value that is less than 1 inch with a 0Express a specified dimension to the same number of decimal places as its toleranceFractional inches generally indicate larger tolerance
28Proper Use of Inch Units Plus and minus tolerance values have the same number of decimal placesUnilateral tolerances use the + and – signThe 0 value has the same number of decimal places as the value that is greater or less than 0Limit tolerance values have the same number of decimal points
29Proper Use of Angular Units Use decimal or degrees–minutes–seconds formatAngle and tolerance values have the same number of decimal placesInclude 0°or 0°0″ when specifying only minutes or seconds, as applicable
30Using Fractions Not as common as decimal inches or millimeters Architectural and structural drawingsGenerally indicate larger tolerance
31Arrowheads Terminate dimension lines and leaders Three times as long as they are wideConsistent sizeFilled in solid or open
32Dimension Line Spacing First dimension line:Uniform distance from the object.375 in. (10 mm) minimumin. ( mm) preferredSucceeding dimension lines:Equally spaced.25 in. (6 mm) minimumin. ( mm) preferred
40Preferred Dimensioning Practices Avoid crossing extension linesDo not break extension lines when they crossNever cross extension lines over dimension linesBreak the extension line where it crosses over a dimension line when necessary
41Preferred Dimensioning Practices Never break a dimension lineBreak extension lines when they cross over or near an arrowheadAvoid dimensioning over or through the objectAvoid dimensioning to hidden features
42Preferred Dimensioning Practices Avoid long extension linesAvoid using any line of the object as an extension lineDimension between views when possibleGroup adjacent dimensions
43Preferred Dimensioning Practices Dimension to views that provide the best shape descriptionDo not use a centerline, extension line, phantom line, visible object line, or a continuation of any of these lines as a dimension lineStagger adjacent dimension numerals so they do not line up
70General Notes and Specifications Sheet blocks:Outside sheet blocks:MaterialMachining practicesGeneral tolerancesCommon dimensionsScaleFinish or other treatmentsPart nameSheet sizePart numberNumber of revisionsProjection
71Flag Notes Delta note Specific note placed with general notes Keyed to the drawingDelta symbol (Δ) commonHexagons and circles also used
72Tolerances Help ensure parts fit together and function in an assembly Apply to all dimensions on a drawing, except:ReferenceMaximumMinimumStock size
73Plus-Minus Dimensioning Calculate the upper and lower limits from the specified dimension and plus-minus toleranceBilateral toleranceMost common tolerancing methodEqual bilateral tolerance[Insert 6.5 0.2, match to unequal bilateral tolerance style]Often preferred by manufacturesUnequal bilateral tolerance[Insert ]
74[Insert , match to unequal bilateral tolerance style] Unilateral Tolerance[Insert , match to unequal bilateral tolerance style]Used by some companies to define fits between mating partsOften avoided by CNC machine programmers
75Limit DimensioningCalculate the tolerance from the upper and lower limitsCommon for defining fits between mating partsPreferred by some companies or departments
76Single Limits Can be used for common machine processes Follow dimension value with (MIN) or (MAX)Design determines unspecified limit
84Interference Fit Force or shrink fit Examples: Bushing pressed onto a housingPin is pressed into a hole
85Extreme Form Variation Established by limits of sizeSpecified by “Rule 1” in ASME Y14.5
86Limits and Fits Between Mating Parts Fit determined first based on the use or serviceLimits of size established second to ensure the desired fitANSI/ASME B4.1 Preferred Limits and Fits for Cylindrical PartsANSI/ASME B4.2 Preferred Metric Limits and FitsTables of establishing dimensions for standard ANSI fits
87Running and Sliding Fits (RFC) RC1—Close sliding fitsRC2—Sliding fitsRC3—Precision running fitsRC4—Close running fitsRC5 and RC6—Medium running fitsRC7—Free running fitsRC8 and RC9—Loose running fits
90Dimensions Applied to Platings and Coatings General note:DIMENSIONAL LIMITS APPLY BEFORE (AFTER) PLATING (COATING)Specific note:Leader with a dot pointing to the specific surface instead of an arrowhead
91Casting Drawing and Design Depends on:Casting process and characteristicsMaterialDesign or shape of the partDie or moldBased on ASME Y14.8, Castings and Forgings standard
92Shrinkage Allowance Extra material to account for cooling Examples: Iron .125 in. per ft. (.4 mm per meter)Steel .250 in. per ft.Aluminum .125 to .156 in. per ft. (.4 mm–.5 per meter)Brass .22 in. per ft. (.7 mm per meter)Bronze .156 in. per ft. (.5 mm per meter)Patternmaker applies shrink rules
93Draft Not necessary on horizontal surfaces Begin at the parting line and parting planeTapers away from the molding material
94Draft on a Drawing General note: Angular dimensions ALL DRAFT ANGLES .010ALL DRAFT ANGLES 6°Angular dimensionsPlus draft and/or minus draft methods
96Fillets and Rounds in Casting Allow the pattern to eject freely from the moldFillets help reduce the tendency of cracks to develop during shrinkageRadii determined by part thickness
97Machining Allowance Extra material for any surface to be machined Examples:Iron and steel .125 in. (3 mm)Brass, bronze, and aluminum .062 in. (1.5 mm)Greater for large castings or those with a tendency to warp
98Casting Drawings Casting drawing Machining drawing Combined casting and machining drawingDrawing phantom lines to show machining allowance and draft angles
99Forging Design and Drawing Focuses on diesDraftFillets and roundsMachining allowanceBased on ASME Y14.8, Castings and Forgings standard
100Forging Drawings Stock material drawings: Detail drawings Show size and shape of the stock materialOutline of the end product using phantom linesDetail drawingsShow the end productUsually show draftUse phantom lines to show machining allowance and draft angles
101Surface Finish (Surface Texture) Obtained by:MachiningGrindingHoningLappingSpecified using surface finish symbol
104Design and Drafting of Machined Features Capabilities of the machinery availableLeast-expensive method to get the desired resultAvoid over-machining
105Tool Design Jig and fixture design Machining operations require special tools to hold the workpiece or guide the machine toolInvolves knowledge of:KinematicsMachining operationsMachine tool functionMaterial handlingMaterial characteristics
106Jig and Fixture Drawings Assembly drawing with all components of the toolFast-acting clampsSpring-loaded positionersClamp strapsQuick-release locating pinsHandlesKnobs
108Tools in Manufacturing Drill jigsDatumsDrill fixturesMachining fixturesWelding fixturesInspection fixturesProgressive dies
109Qualities of Tools Reliability Repeatability Ease of use Ease of manufactureEase of maintenance and repair
110Basic Elements of Tool Design Visualizing how shop personnel will accomplish a specific taskConceptualizing hardware to assist in the accomplishment of that taskCreating drawings so the hardware can be manufactured
111Introduction to ISO 9000 ISO 9000-1 ISO 9001 ISO 9002 Direction and definitions that describe what each standard containsAssists companies in the selection and use of the appropriate ISO standardISO 9001Model for designing, documenting, and implementing ISO standardsISO 9002ISO 9001 but does not contain the requirement of documenting the design and development process
112Introduction to ISO 9000 ISO 9003 ISO 9004-1 Companies or organizations that only need to demonstrate through inspection and testing methods that they are providing the desired product or serviceISOSet of guidelines for development and implementation of a quality management system
113Glossary Actual size Allowance The measured size of a feature or part after manufacturing.AllowanceThe tightest possible fit between two mating parts.
114Glossary Baseline dimensioning Basic dimension Bilateral tolerance A common method of dimensioning machine parts whereby each feature dimension originates from a common surface, axis, or center plane.Basic dimensionA theoretically exact size, location, profile, or orientation of a feature or point.Bilateral toleranceA tolerance allowed to vary in two directions from the specified dimension.
115Glossary Bilateral tolerance Blind hole Casting A tolerance in which variation is permitted in both directions from the specified dimension.Blind holeA hole that does not go through.CastingAn object or part produced by pouring molten metal into a mold.
116Glossary Chain dimensioning Chamfer Clearance fit Also known as point-to-point dimensioning, a method of dimensioning from one feature to the next.ChamferA slight surface angle used to relieve a sharp corner.Clearance fitA condition when, due to the limits of dimensions, there is always a clearance between mating parts.
117Glossary Controlled radius Counterbore Counterdrill The limits of the radius tolerance zone must be tangent to the adjacent surfaces, and there can be no reversals in the contour.CounterboreOften used to machine a diameter below the surface of a part so a bolt head or other fastener can be recessed.CounterdrillA combination of two drilled features.
118Glossary Countersink Datum Delta A conical feature in the end of a machined hole.DatumA theoretically exact surface, plane, axis, center plane, or point from which dimensions for related features are established.DeltaA triangle symbol (Δ) placed on the drawing for reference.
119Glossary Diameter Die Dimension The distance across a circle measured through the center.DieAny device used to produce a desired shape, form or finish to a material.DimensionA numerical value or values, or mathematical expression provided in appropriate units of measure and used to define form, size, orientation or location of a feature or part.
120Glossary Direct dimensioning Draft Equal bilateral tolerance Dimensioning applied to control the size or location of one or more specific features.DraftThe taper allowance on all vertical surfaces of a pattern, which is necessary to facilitate the removal of the pattern from the mold.Equal bilateral toleranceA tolerance where the variation from the specified dimension is the same in both the + and – directions.
121Glossary Extreme form variation Feature of size Feature The variation of the form of the feature between the upper limit and lower limit of a size dimension.Feature of sizeOne cylindrical or spherical surface, a circular element, or a set of two opposed elements or opposed parallel plane surfaces, each of which is associated with a directly toleranced dimension.FeatureThe general term applied to describe a physical portion of a part or object, such as a surface, slot, tab, pin, keyseat, or hole.
122Glossary Forging Free state condition General notes A process of shaping malleable metals by hammering or pressing between dies that duplicate the desired shape.Free state conditionDistortion of the part after removal of forces applied during manufacturing.General notesInformation that relates to the entire drawing.
123Glossary General notes Geometric tolerance Interference fit Notes placed separate from the views and relate to the entire drawing.Geometric toleranceThe general term applied to the category of tolerances used to control size, form, profile, orientation, location, and runout.Interference fitThe condition that exists when, due to the limits of the dimensions, mating parts must be pressed together.
124Glossary Keyseat Keyway Kinematics A groove or channel cut in a shaft. A shaft and key are inserted into a hub, wheel, or pulley where the key mates with a groove called a keyway.KinematicsThe study of mechanisms.
125Glossary Knurling Lay Least material condition (LMC) A cold forming process used to form a cylindrical or flat surface uniformly with a diamond or straight pattern creating a knurl.LayThe direction or configuration of the predominant surface pattern.Least material condition (LMC)The condition where a feature contains the least amount of material allowed by the size limits.
126Glossary Least material condition (LMC) Limit dimensioning The opposite of MMC, the least amount of material possible in the size of a feature within the stated limits.Limit dimensioningA system of dimensioning where the upper and lower limits of the tolerance are provided and there is no specified dimension given.Limits of dimensionThe largest and smallest possible boundary to which a feature can be made as related to the tolerance of the dimension.
127Glossary Limits of size Local notes (specific notes) The amount of variation in size and geometric form of a feature control. The boundary between maximum material condition (MMC) and least material condition (LMC).Local notes (specific notes)Notes connected to specific features on the views of the drawing.Location dimensionsDimensions that provide the relationship of features of an object.
128Glossary Locational fits (LC, LT, LN) Maximum material condition (MMC) Provide rigid or accurate location, as with interference fits, or provide some freedom of location, as with clearance fits.Maximum material condition (MMC)The condition of a part or feature when it contains the most amount of material within the stated limits.
129Glossary Mold Neck Nominal size A form made to pour or inject material to produce the desired shape.NeckThe result of a machining operation that establishes a narrow groove on a cylindrical part or object.Nominal sizeA dimension used for general identification such as stock size or thread diameter.
130Glossary Nonrigid parts Notes Parting line Parts that can have dimensional change due to thin wall characteristics.NotesA type of dimension that generally identify the size of a feature or features with written specifications that are more detailed than a numerical value.Parting lineThe separation between the mold or die components, and is a line on the drawing representing the mating surfaces between the mold or die components.
131Glossary Parting plane Patternmaker Plus-minus dimensioning The mating surfaces of a die or mold.PatternmakerA person who makes a pattern for casting and forging applications.Plus-minus dimensioningA system of dimensioning that provides a nominal dimension and an amount of allowable variance from that dimension.
132Glossary Polar coordinate dimensioning Radius Using angular dimensions to locate features from planes or centerlines.RadiusThe distance from the center of a circle to the outside.Rectangular coordinate dimensioningUsing linear dimensions to locate features from planes or centerlines.
133Glossary Reference dimension Running and sliding fits (RFC) A dimension used for information purposes only and is usually without a tolerance.Running and sliding fits (RFC)Intended to provide a similar running performance with suitable lubrication allowance throughout their range of sizes.Single limitsUsed when the specified dimension cannot be any more than the maximum or less than the minimum given value.
134Glossary Size dimensions Specifications Specified dimension Dimensions placed directly on a feature to identify a specific size or may be connected to a feature in the form of a note.SpecificationsAny written information or instructions included on the drawing or with a set of drawings, giving all necessary information not shown in the drawing field.Specified dimensionThe part of the dimension from which the limits are calculated.
135Glossary Spotface Statistical tolerancing Stock size Provides a flat bearing surface for a washer face or bolt head.Statistical tolerancingThe assigning of tolerances to related dimensions in an assembly based on the requirements of statistical process control (SPC).Stock sizeA commercial or pre-manufactured size, such as a particular size of square, round, or hex steel bar.
136Glossary Surface finish (surface texture) Surface roughness The roughness, waviness, lay, and flaws of a surface.Surface roughnessFine irregularities in the surface finish and is a result of the manufacturing process used.Surface wavinessThe often widely spaced condition of surface texture usually caused by such factors as machine chatter, vibrations, work deflection, warpage, or heat treatment
137Glossary Tolerance stacking (tolerance buildup) Tolerance True radius The tolerance of each dimension builds on the next.ToleranceThe total permissible variation in size or location.True radiusThe actual radius of an arc even though it may be shown not true size and shape.
138Glossary Unequal bilateral tolerance Unilateral tolerance A tolerance where the variation from the specified dimension is not the same in both directions.Unilateral toleranceA tolerance where the variation is permitted to increase or decrease in only one direction from the specified dimension.