Presentation on theme: "CHAPTER 10 Dimensioning and Tolerancing. Learning Objectives Identify and use common dimensioning systems Explain and apply dimensioning standards based."— Presentation transcript:
CHAPTER 10 Dimensioning and Tolerancing
Learning Objectives Identify and use common dimensioning systems Explain and apply dimensioning standards based on ASME Y 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) Local notes (specific notes) General notes General notes
ASME Dimensioning Standards ASME Y14.5, Dimensioning and Tolerancing General note: DIMENSIONING AND TOLERANCING PER ASME Y 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 toleranceGeometric tolerance Least material condition (LMC)Least material condition (LMC) Limits of dimensionLimits of dimension
Dimensioning Definitions Maximum material condition (MMC)Maximum material condition (MMC) Nominal size Radius Reference dimensionReference dimension Stock size Specified dimensionSpecified dimension Tolerance Unilateral toleranceUnilateral 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 partsfree state conditionnonrigid 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
Rectangular Coordinate Dimensioning without Dimension Lines
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 in. ( mm) preferred Succeeding dimension lines: Equally spaced .25 in. (6 mm) minimum in. ( mm) preferred
Chain Dimensioning Creates tolerance stacking (tolerance buildup)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
Dimensioning Symmetrical Objects
Dimensioning Square Features
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 Angular Surfaces
Dimensioning Conical Shapes
Dimensioning Hexagons and Other Polygons Dimension across the flats
Dimensioning Arc Radius
Dimensioning Arc Length
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
Dimensioning Contours Not Defined as Arcs Dimension coordinates or points along the contour from common surfaces Series of dimensions on the object and along the contour Tabular dimensioning
Locating a Point Established by Extension Lines
Dimensioning Circles and Thru Holes
Dimensioning Blind HolesBlind Holes
Dimensioning a CounterboreCounterbore
Dimensioning a SpotfaceSpotface
CountersinkCountersink or CounterdrillCounterdrill
Dimensioning Multiple Features Number of features, X, a space, feature specification Dimension to one of the features only Examples: 4X Ø6 THRU or 4X Ø6 2X R.50 3X 8X45°
Dimensioning Keyseats and KeywaysKeyseatsKeyways
Dimensioning Necks and GroovesNecks
Rectangular Coordinate Dimensioning
Polar Coordinate Dimensioning
Dimensioning Repetitive Features
Locating Multiple Tabs in a Polar Orientation
Locating Multiple Features of Nearly the Same Size
Specifying Dimension Origin Clearly identifies from which feature the dimension originates
Dimensioning Auxiliary Views
General Notes and Specifications Sheet blocks: Material General tolerances Scale Part name Sheet size Part number Number of revisions Projection Outside sheet blocks: Machining practices Common dimensions Finish or other treatments
Flag Notes Delta noteDelta Specific note placed with general notes Keyed to the drawing Delta symbol (Δ) common Hexagons and circles also used
Tolerances Help ensure parts fit together and function in an assembly Apply to all dimensions on a drawing, except: Reference Maximum Minimum Stock size
Plus-Minus Dimensioning Calculate the upper and lower limits from the specified dimension and plus-minus tolerancelimitsspecified dimension Bilateral tolerance Most common tolerancing method Equal bilateral tolerance [Insert 6.5 0.2, match to unequal bilateral tolerance style] Often preferred by manufactures Unequal bilateral tolerance [Insert ]
Unilateral Tolerance [Insert, match to unequal bilateral tolerance style] Used by some companies to define fits between mating parts Often avoided by CNC machine programmers
Limit Dimensioning Calculate the tolerance from the upper and lower limits Common for defining fits between mating parts Preferred by some companies or departments
Single Limits Can be used for common machine processes Follow dimension value with (MIN) or (MAX) Design determines unspecified limit
Specified and Unspecified Inch Tolerances
Specified and Unspecified Metric Tolerances ISO 2768 classes of size tolerances: Fine (f) Medium (m) Coarse (c) Very coarse (v)
Interference Fit Force or shrink fit Examples: Bushing pressed onto a housing Pin is pressed into a hole
Extreme Form Variation Established by limits of sizelimits of size Specified by “Rule 1” in ASME Y14.5
Limits and Fits Between Mating Parts Fit determined first based on the use or service Limits of size established second to ensure the desired fit ANSI/ASME B4.1 Preferred Limits and Fits for Cylindrical Parts ANSI/ASME B4.2 Preferred Metric Limits and Fits Tables of establishing dimensions for standard ANSI fits
Running and Sliding Fits (RFC) RC1—Close sliding fits RC2—Sliding fits RC3—Precision running fits RC4—Close running fits RC5 and RC6—Medium running fits RC7—Free running fits RC8 and RC9—Loose running fits
Force Fits (FN) FN1—Light drive fits FN2—Medium drive fits FN3—Heavy drive fits FN4 and FN5—Force fits
Dimensions 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
CastingCasting Drawing and Design Depends on: Casting process and characteristics Material Design or shape of the part Die or mold Diemold Based on ASME Y14.8, Castings and Forgings standard
Shrinkage 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 rulesPatternmaker
Draft Not necessary on horizontal surfaces Begin at the parting line and parting planeparting lineparting plane Tapers away from the molding material
Draft on a Drawing General note: ALL DRAFT ANGLES.010 ALL DRAFT ANGLES 6° Angular dimensions Plus draft and/or minus draft methods
Parting Lines on a Drawing
Fillets and Rounds in Casting Allow the pattern to eject freely from the mold Fillets help reduce the tendency of cracks to develop during shrinkage Radii determined by part thickness
Machining 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
Casting Drawings Casting drawing Machining drawing Combined casting and machining drawing Drawing phantom lines to show machining allowance and draft angles
Forging Design and Drawing Focuses on dies Draft Fillets and rounds Machining allowance Based on ASME Y14.8, Castings and Forgings standard
Forging Drawings Stock material drawings: Show size and shape of the stock material Outline of the end product using phantom lines Detail drawings Show the end product Usually show draft Use phantom lines to show machining allowance and draft angles
Surface Finish (Surface Texture) Obtained by: Machining Grinding Honing Lapping Specified using surface finish symbol
Design and Drafting of Machined Features Capabilities of the machinery available Least-expensive method to get the desired result Avoid over-machining
Tool Design Jig and fixture design Machining operations require special tools to hold the workpiece or guide the machine tool Involves knowledge of: Kinematics Machining operations Machine tool function Material handling Material characteristics
Jig and Fixture Drawings Assembly drawing with all components of the tool Fast-acting clamps Spring-loaded positioners Clamp straps Quick-release locating pins Handles Knobs
Jig and Fixture Drawings
Tools in Manufacturing Drill jigs Datums Drill fixtures Machining fixtures Welding fixtures Inspection fixtures Progressive dies
Qualities of Tools Reliability Repeatability Ease of use Ease of manufacture Ease of maintenance and repair
Basic Elements of Tool Design 1.Visualizing how shop personnel will accomplish a specific task 2.Conceptualizing hardware to assist in the accomplishment of that task 3.Creating drawings so the hardware can be manufactured
Introduction to ISO 9000 ISO Direction and definitions that describe what each standard contains Assists companies in the selection and use of the appropriate ISO standard ISO 9001 Model for designing, documenting, and implementing ISO standards ISO 9002 ISO 9001 but does not contain the requirement of documenting the design and development process
Introduction to ISO 9000 ISO 9003 Companies or organizations that only need to demonstrate through inspection and testing methods that they are providing the desired product or service ISO Set of guidelines for development and implementation of a quality management system
Glossary Actual size The measured size of a feature or part after manufacturing. Allowance The tightest possible fit between two mating parts. Allowance The tightest possible fit between two mating parts.
Glossary Baseline dimensioning A common method of dimensioning machine parts whereby each feature dimension originates from a common surface, axis, or center plane. Basic dimension A theoretically exact size, location, profile, or orientation of a feature or point. Bilateral tolerance A tolerance allowed to vary in two directions from the specified dimension.
Glossary Bilateral tolerance A tolerance in which variation is permitted in both directions from the specified dimension. Blind hole A hole that does not go through. Casting An object or part produced by pouring molten metal into a mold.
Glossary Chain dimensioning Also known as point-to-point dimensioning, a method of dimensioning from one feature to the next. Chamfer A slight surface angle used to relieve a sharp corner. Clearance fit A condition when, due to the limits of dimensions, there is always a clearance between mating parts.
Glossary Controlled radius The limits of the radius tolerance zone must be tangent to the adjacent surfaces, and there can be no reversals in the contour. Counterbore Often used to machine a diameter below the surface of a part so a bolt head or other fastener can be recessed. Counterdrill A combination of two drilled features.
Glossary Countersink A conical feature in the end of a machined hole. Datum A theoretically exact surface, plane, axis, center plane, or point from which dimensions for related features are established. Delta A triangle symbol (Δ) placed on the drawing for reference.
Glossary Diameter The distance across a circle measured through the center. Die Any device used to produce a desired shape, form or finish to a material. Dimension A 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.
Glossary Direct dimensioning Dimensioning applied to control the size or location of one or more specific features. Draft The taper allowance on all vertical surfaces of a pattern, which is necessary to facilitate the removal of the pattern from the mold. Equal bilateral tolerance A tolerance where the variation from the specified dimension is the same in both the + and – directions.
Glossary Extreme form variation The variation of the form of the feature between the upper limit and lower limit of a size dimension. Feature of size One 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. Feature The general term applied to describe a physical portion of a part or object, such as a surface, slot, tab, pin, keyseat, or hole.
Glossary Forging A process of shaping malleable metals by hammering or pressing between dies that duplicate the desired shape. Free state condition Distortion of the part after removal of forces applied during manufacturing. General notes Information that relates to the entire drawing.
Glossary General notes Notes placed separate from the views and relate to the entire drawing. Geometric tolerance The general term applied to the category of tolerances used to control size, form, profile, orientation, location, and runout. Interference fit The condition that exists when, due to the limits of the dimensions, mating parts must be pressed together.
Glossary Keyseat A groove or channel cut in a shaft. Keyway A shaft and key are inserted into a hub, wheel, or pulley where the key mates with a groove called a keyway. Kinematics The study of mechanisms.
Glossary Knurling A cold forming process used to form a cylindrical or flat surface uniformly with a diamond or straight pattern creating a knurl. Lay The 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.
Glossary Least material condition (LMC) The opposite of MMC, the least amount of material possible in the size of a feature within the stated limits. Limit dimensioning A system of dimensioning where the upper and lower limits of the tolerance are provided and there is no specified dimension given. Limits of dimension The largest and smallest possible boundary to which a feature can be made as related to the tolerance of the dimension.
Glossary Limits of size 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 dimensions Dimensions that provide the relationship of features of an object.
Glossary Locational fits (LC, LT, LN) 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.
Glossary Mold A form made to pour or inject material to produce the desired shape. Neck The result of a machining operation that establishes a narrow groove on a cylindrical part or object. Nominal size A dimension used for general identification such as stock size or thread diameter.
Glossary Nonrigid parts Parts that can have dimensional change due to thin wall characteristics. Notes A 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 line The separation between the mold or die components, and is a line on the drawing representing the mating surfaces between the mold or die components.
Glossary Parting plane The mating surfaces of a die or mold. Patternmaker A person who makes a pattern for casting and forging applications. Plus-minus dimensioning A system of dimensioning that provides a nominal dimension and an amount of allowable variance from that dimension.
Glossary Polar coordinate dimensioning Using angular dimensions to locate features from planes or centerlines. Radius The distance from the center of a circle to the outside. Rectangular coordinate dimensioning Using linear dimensions to locate features from planes or centerlines.
Glossary Reference dimension 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 limits Used when the specified dimension cannot be any more than the maximum or less than the minimum given value.
Glossary Size dimensions Dimensions placed directly on a feature to identify a specific size or may be connected to a feature in the form of a note. Specifications Any 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 dimension The part of the dimension from which the limits are calculated.
Glossary Spotface Provides a flat bearing surface for a washer face or bolt head. Statistical tolerancing The assigning of tolerances to related dimensions in an assembly based on the requirements of statistical process control (SPC). Stock size A commercial or pre-manufactured size, such as a particular size of square, round, or hex steel bar.
Glossary Surface finish (surface texture) The roughness, waviness, lay, and flaws of a surface. Surface roughness Fine irregularities in the surface finish and is a result of the manufacturing process used. Surface waviness The often widely spaced condition of surface texture usually caused by such factors as machine chatter, vibrations, work deflection, warpage, or heat treatment
Glossary Tolerance stacking (tolerance buildup) The tolerance of each dimension builds on the next. Tolerance The total permissible variation in size or location. True radius The actual radius of an arc even though it may be shown not true size and shape.
Glossary Unequal bilateral tolerance A tolerance where the variation from the specified dimension is not the same in both directions. Unilateral tolerance A tolerance where the variation is permitted to increase or decrease in only one direction from the specified dimension.