CHAPTER 10

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

Dimensions

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

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


• 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


• 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


• 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


• 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

Dimensioning Components

Dimensioning Symbols

Unidirectional Dimensioning

Aligned Dimensioning

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

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

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

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

Dimension Numerals

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

Dimensioning Symmetrical Objects

Dimensioning Cylinders

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


• 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


• Avoid long extension lines• Avoid using any line of the object

as an extension line• Dimension between views when

possible• Group adjacent dimensions


• 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 Chamfers

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 Holes

Dimensioning a Counterbore

Dimensioning a Spotface

Countersink or Counterdrill

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 Slots

Dimensioning Keyseats and Keyways

Dimensioning Knurls

Dimensioning Necks and Grooves

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

Flag Notes

• Delta note• 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 tolerance

• 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

Applying Statistical Tolerancing

Maximum Material Condition (MMC)

• External feature is at MMC at its largest limit

• Internal feature is at MMC at its smallest limit

Least Material Condition (LMC)

• External feature is at LMC at its smallest limit

• Internal feature is at LMC at its largest limit

Clearance Fit

Allowance

MMC Internal Feature– MMC External Feature Allowance

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 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

Locational Fits (LC, LT, LN)

• LC—Locational clearance fits• LT—Locational transition fits• LN—Locational interference 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

Casting Drawing and Design

• Depends on:• Casting process and characteristics

• Material

• Design or shape of the part

• Die or mold

• 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 rules

Draft

• Not necessary on horizontal surfaces

• Begin at the parting line and parting 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

Surface Finish Characteristics

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 9000-1• 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 9004-1• Set of guidelines for development and

implementation of a quality management system

CHAPTER 10

Documents

Transcript of CHAPTER 10