product specificationdimensioning and tolerancing

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    Product specification

    Dimensioning and tolerancing

    It is impossible to make a perfectcomponent so when we design a part

    we specify the acceptable range offeatures that make-up the part.

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    IE 316 ManufacturingEngineering I - Processes

    Chapter 2 Suppliment

    DIMENSIONS, TOLERANCES, AND

    SURFACES

    Dimensions, Tolerances, and Related Attributes

    Surfaces

    ASME Y14.5 Form Geometry

    Effect of Manufacturing Processes

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    THE DESIGN PROCESS

    Product Engineering

    Design Process

    Off-road bicycle that ...

    1. Conceptualization

    2. Synthesis3. Analysis

    4. Evaluation

    5. Representation

    Design ProcessHow can this be

    accomplished?

    1. Clarification of the task

    2. Conceptual design

    3. Embodiment design

    4. Detailed design

    Functional requirement -> Design

    Steps 1 & 2 Select material and properties, begin geometricmodeling (needs creativity, sketch is sufficient)

    3 mathematical, engineering analysis4 simulation, cost, physical model5 formal drawing or modeling

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    DESIGN REPRESENTATION

    Design EngineeringRepresentation

    Manufac-turing

    Verbal

    Sketch Multi-view orthographic drawing (drafting)

    CAD drafting

    CAD 3D & surface model

    Solid model

    Feature based design

    Requirement of the representation method

    precisely convey the design concept

    easy to use

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    A FREE-HAND SKETCHOrthographic Projection

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    A FORMAL 3-VIEW DRAWING

    0.9444"

    4 holes 1/4" dia

    around 2" dia , first

    hole at 45

    A

    2.0000.001

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    DESIGN DRAFTING

    Third angle projection

    Profile plane

    Y

    Z

    XIII

    Horizontal

    Frontal plane

    I

    IV

    II

    top

    front

    side

    a

    b c d ef

    g

    h i

    j

    Drafting in the third angle

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    INTERPRETING A DRAWING

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    DESIGN DRAFTING

    Partial view

    Cut off view and auxiliary view

    Provide more local details

    A

    2.0000.001

    AA

    A-A

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    TOLERANCE

    Dimensional tolerance - conventional

    Geometric tolerance - modern

    unilateral

    bilateral

    1.00 0.05+-

    nominal dimension

    tolerance

    0.95+ 0.10- 0.00 1.05

    + 0.00- 0.10

    1.00 0.05+-

    0.95 - 1.05means a range

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    TOLERANCE STACKING

    "TOLERANCE IS ALWAYS ADDITIVE" why?

    What is the expected dimension and tolerances?

    d = 0.80 +1.00 + 1.20 = 3.00

    t = (0.01 + 0.01 + 0.01) = 0.03

    0.80 ' 0.01 1.20 ' 0.01

    1.00 ' 0.01

    ?

    1. Check that the tolerance & dimension specifications arereasonable - for assembly.

    2. Check there is no over or under specification.

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    TOLERANCE STACKING (ii)

    What is the expected dimension and tolerances?

    d = 3.00 - 0.80 - 1.20 = 1.00

    t = (0.01 + 0.01 + 0.01) = 0.03

    0.80 ' 0.01 1.20 ' 0.01

    3.00 ' 0.01

    ?

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    TOLERANCE STACKING (iii)

    Maximum x length = 3.01 - 0.79 - 1.19 = 1.03Minimum x length = 2.99 - 0.81 - 1.21 = 0.97

    Therefore x = 1.00 0.03

    0.80 ' 0.01 1.20 ' 0.01

    3.00 ' 0.01?

    x

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    TOLERANCE GRAPH

    G(N,d,t)

    N: a set of reference lines, sequenced nodes

    d: a set of dimensions, arcs

    t: a set of tolerances, arcs

    A B C D Ed,t d,t d,td,t

    d : dimension between references i & j

    t : tolerance between references i & jij

    ij

    Reference i is in front of reference j in the sequence.

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    EXAMPLE TOLERANCE GRAPH

    A B C D E

    A B C D Ed,td,t d,t

    d,t

    different propertiesbetween d & t

    dDE= d

    DA+ d

    AE=

    dAD+ d

    AE

    = (dAB+ d

    BC+ d

    CD) + d

    AE

    tDE= tAB+ tBC+ tCD + tAE

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    OVER SPECIFICATIONIf one or more cycles can be detected in the graph, we say that the dimension

    and tolerance are over specified.

    A B C

    A B C

    A B C

    d1 d2

    d3d1,t1 d2,t2

    d3,t3

    t1 t2

    t3

    Redundant dimension

    Over constraining tolerance(impossible to satisfy) why?

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    UNDER SPECIFICATION

    A B C D E

    A B C D Ed1 d2

    d3

    C D is disconnected from the

    rest of the graph.

    No way to find dBC and dDE

    When one or more nodes are disconnected from the graph, the

    dimension or tolerance is under specified.

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    PROPERLY TOLERANCED

    A B C D E

    A B C D Ed,td,t d,t

    d,t

    dDE= d

    DA+ d

    AE= dAD+ dAE

    = (dAB+ d

    BC+ d

    CD) + d

    AE

    tDE= tAB+ tBC+ tCD + tAE

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    TOLERANCE ANALYSISFor two or three dimensional tolerance analysis:

    i. Only dimensional tolerance

    Do one dimension at a time.

    Decompose into X,Y,Z, three one dimensional problems.

    ii. with geometric tolerance

    ? Don't have a good solution yet. Use simulation?

    true position

    diameter & tolerance

    A circular tolerance zone, the size is influencedby the diameter of the hole. The shape of thehole is also defined by a geometric tolerance.

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    3-D GEOMETRIC TOLERANCE

    PROBLEMS

    t

    datum surfacedatumsurface

    Referenceframe

    perpendicularity

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    TOLERANCE ASSIGNMENT

    Tolerance is money

    Specify as large a tolerance as possible as long as functional and assemblyrequirements can be satisfied.

    (ref. Tuguchi, ElSayed, Hsiang, Quality Engineering in Production Systems,McGraw Hill, 1989.)

    function

    cost

    Tolerance value

    d (nominal dimension)

    Quality

    Cost

    - t

    +t

    Quality cost

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    REASON OF HAVING TOLERANCE

    No manufacturing process is perfect.

    Nominal dimension (the "d" value) cannot be achieved exactly.

    Without tolerance we lose the control andas a consequence cause functional orassembly failure.

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    EFFECTS OF TOLERANCE (I)

    1. Functional constraints

    e.g.

    d t

    flow rate

    Diameter of the tube affects the flow. What is the allowedflow rate variation (tolerance)?

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    EFFECTS OF TOLERANCE (II)

    2. Assembly constraints

    e.g. peg-in-a-hole dp

    dh

    How to maintain theclearance?

    Compound fitting

    The dimension of eachsegment affectsothers.

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    RELATION BETWEEN

    PRODUCT & PROCESS

    TOLERANCES

    Setuplocators

    0.005

    0.005

    0.005

    Design specifications

    Process tolerance

    Machine uses the locators as thereference. The distances from themachine coordinate system to thelocators are known.

    The machining tolerance is measuredfrom the locators.

    In order to achieve the 0.01tolerances, the process tolerancemust be 0.005 or better.

    When multiple setups are used, the

    setup error need to be taken intoconsideration.

    A

    0.01 t olerances

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    TOLERANCE CHARTINGA method to allocate process tolerance and verify that the process sequence

    and machine selection can satisfy the design tolerance.

    0 .01 0 .0 1

    0 .01

    stock

    boundary

    Dim t ol

    1.0 0.01

    1.0 0.01

    3.0 0.01

    Op code

    10 lathe

    10 lathe

    20 lathe

    20 lathe

    10

    12

    20

    22

    blue print

    Operationsequence

    Not shown areprocess toleranceassignment andbalance

    produced tolerances:

    process tol of 10 + process tol of 12

    process tol of 20 + process tol 22

    process tol of 22 + setup tol

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    PROBLEMS WITH DIMENSIONAL

    TOLERANCE ALONE

    1.001

    1.0011.001

    6.00

    1.000.001

    6.000.001

    As designed:

    As manufactured:

    Will you accept the partat right?

    Problem is the control ofstraightness.

    How to eliminate theambiguity?

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    GEOMETRIC TOLERANCES

    FORM

    straightness

    flatness

    Circularity

    cylindricity

    ORIENTATION

    perpendicularity

    angularity

    parallelism

    LOCATION

    concentricity

    true position

    symmetry

    RUNOUT

    circular runouttotal runout

    PROFILEprofileprofile of a line

    ANSI Y14.5M-1977 GD&T (ISO 1101, geometric tolerancing;

    ISO 5458 positional tolerancing; ISO 5459 datums;and others), ASME Y14.5 - 1994

    Squareness

    roundness

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    DATUM &

    FEATURE CONTROL FRAMEDatum: a reference plane, point, line, axis where usually a plane where you can

    base your measurement.

    Symbol:

    Even a hole pattern can be used as datum.

    Feature: specific component portions of a part and may include one or moresurfaces such as holes, faces, screw threads, profiles, or slots.

    Feature Control Frame:

    A

    // 0.005 M A

    symbol tolerance value

    modifier

    datum

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    MODIFIERS

    M Maximum material condition MMC assembly

    Regardless of feature size RFS (implied unless specified)

    L Least material condition LMC less frequently used

    P Projected tolerance zone

    O Diametrical tolerance zone

    T Tangent plane

    F Free state

    maintain critical wall

    thickness or criticallocation of features.

    MMC, RFS, LMC

    MMC, RFS

    RFS

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    SOME TERMS

    MMC : Maximum Material ConditionSmallest hole or largest peg (more material left on the part)

    LMC : Least Material Condition

    Largest hole or smallest peg (less material left on the part)

    Virtual condition:

    Collective effect of all tolerances specified on a feature.

    Datum target points:

    Specify on the drawing exactly where the datum contact points should belocated. Three for primary datum, two for secondary datum and one ortertiary datum.

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    STRAIGHTNESS

    Value must be smaller than

    the size tolerance.

    1.000 '0.002

    0.001

    Measurederror0.001

    1.000 '0.002

    0.001

    0.001

    Design Meaning

    Tolerance zone between two straightness lines.

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    IE 316 ManufacturingEngineering I - Processes

    Dimensions and Tolerances

    In addition to mechanical and physical

    properties, other factors that determine the

    performance of a manufactured product

    include: Dimensions - linear or angular sizes of a

    component specified on the part drawing

    Tolerances- allowable variations from the specifiedpart dimensions that are permitted in

    manufacturing

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    IE 316 ManufacturingEngineering I - Processes

    Surfaces

    Nominalsurface - intended surface contour ofpart, defined by lines in the engineeringdrawing

    The nominal surfaces appear as absolutely straightlines, ideal circles, round holes, and other edgesand surfaces that are geometrically perfect

    Actual surfaces of a part are determined by

    the manufacturing processes used to make it The variety of manufacturing processes result in

    wide variations in surface characteristics

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    IE 316 ManufacturingEngineering I - Processes

    Why Surfaces are Important

    Aesthetic reasons

    Surfaces affect safety

    Friction and wear depend on surface

    characteristics

    Surfaces affect mechanical and physical

    properties

    Assembly of parts is affected by their surfaces

    Smooth surfaces make better electrical contacts

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    IE 316 ManufacturingEngineering I - Processes

    Surface Technology

    Concerned with:

    Defining the characteristics of a surface

    Surface texture

    Surface integrity

    Relationship between manufacturing processes

    and characteristics of resulting surface

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    IE 316 ManufacturingEngineering I - Processes

    Figure 5.2 - A magnified cross-section of a typical metallic part surface

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    IE 316 ManufacturingEngineering I - Processes

    Surface Texture

    The topography and geometric features of the

    surface

    When highly magnified, the surface is

    anything but straight and smooth. It has

    roughness, waviness, and flaws

    It also possesses a pattern and/or direction

    resulting from the mechanical process thatproduced it

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    IE 316 ManufacturingEngineering I - Processes

    Surface Integrity

    Concerned with the definition, specification, andcontrol of the surface layers of a material (mostcommonly metals) in manufacturing andsubsequent performance in service

    Manufacturing processes involve energy whichalters the part surface

    The altered layermay result from work hardening(mechanical energy), or heating (thermal energy),

    chemical treatment, or even electrical energy Surface integrity includes surface texture as well

    as the altered layer beneath

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    IE 316 ManufacturingEngineering I - Processes

    Four Elements of Surface Texture

    1. Roughness - small, finely-spaced deviations

    from nominal surface determined by material

    characteristics and process that formed the

    surface

    2. Waviness - deviations of much larger spacing;

    they occur due to work deflection, vibration,

    heat treatment, and similar factors Roughness is superimposed on waviness

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    IE 316 ManufacturingEngineering I - Processes

    3. Lay-predominantdirection or

    pattern of thesurface texture

    Figure 5.4 - Possible

    lays of a surface

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    IE 316 ManufacturingEngineering I - Processes

    4. Flaws - irregularities that occur occasionally

    on the surface Includes cracks, scratches, inclusions, and

    similar defects in the surface

    Although some flaws relate to surface texture,

    they also affect surface integrity

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    IE 316 ManufacturingEngineering I - Processes

    Surface Roughness

    Average of vertical deviations from nominalsurface over a specified surface length

    Figure 5.5 - Deviations from nominal surface used inthe two definitions of surface roughness

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    IE 316 ManufacturingEngineering I - Processes

    Surface Roughness Equation

    Arithmetic average (AA) is generally used, based onabsolute values of deviations, and is referred toas average roughness

    where Ra = average roughness; y= vertical deviation

    from nominal surface (absolute value); and Lm =specified distance over which the surfacedeviations are measured

    dxL

    yR

    m

    a

    L

    m0

    A Al i S f R h

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    IE 316 ManufacturingEngineering I - Processes

    An Alternative Surface Roughness

    Equation

    Approximation of previous equation is perhapseasier to comprehend:

    where Ra has the same meaning as above; yi=

    vertical deviations (absolute value) identifiedby subscript i; and n = number of deviationsincluded in Lm

    n

    i

    ianyR

    1

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    IE 316 ManufacturingEngineering I - Processes

    Cutoff Length

    A problem with the Ra computation is thatwaviness may get included

    To deal with this problem, a parameter called

    the cutoff length is used as a filter to separatewaviness from roughness deviations

    Cutoff length is a sampling distance along thesurface. A sampling distance shorter than thewaviness width eliminates waviness deviationsand only includes roughness deviations

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    IE 316 ManufacturingEngineering I - Processes

    Figure 5.6 - Surface texture symbols in engineering drawings:

    (a) the symbol, and (b) symbol with identification labels

    Values ofRa are given in microinches; units for other measures are given

    in inchesDesigners do not always specify all of the parameters on engineering

    drawings

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    TRUE POSITION

    1.200.01

    1.000.01

    1.20

    1.00

    Tolerancezone0.01dia

    O0.01MABO.800.02

    Dimensionaltolerance

    True position

    tolerance

    Hole center tolerance zone

    A

    B

    Tolerancezone0.022

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    HOLE TOLERANCE ZONE

    Tolerance zone for dimensional tolerancedhole is not a circle. This causes some assemblyproblems.

    For a hole using true position tolerancethe tolerance zone is a circular zone.

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    TOLERANCE VALUE MODIFICATION

    Produced True Pos tol

    hole size

    0.97 out of diametric tolerance

    0.98 0.01 0.05 0.01

    0.99 0.02 0.04 0.01

    1.00 0.03 0.03 0.01

    1.01 0.04 0.02 0.01

    1.02 0.05 0.01 0.01

    1.03 out of diametric tolerance

    1.20

    1.00

    O0.01MABO1.000.02

    M L S

    The default modifier fortrue position is MMC.

    MMC

    LMC

    For M the allowable tolerance = specified tolerance + (produced holesize - MMC hole size)

    A

    B

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    MMC HOLE

    Given the same peg (MMC peg), when the produced hole size is greaterthan the MMC hole, the hole axis true position tolerance zone can beenlarged by the amount of difference between the produced hole sizeand the MMC hole size.

    hole axis tolerance zone

    MMC holeLMC hole

    MMC peg will fit in t he hole

    axis must be in the tolerance zone,

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    PROJECTED TOLERANCE ZONEApplied for threaded holes or press fit holes to ensure interchangeability

    between parts. The height of the projected tolerance zone is the thicknessof the mating part.

    O.010MABC.250p

    .375-16UNC-2B

    Project ed t olerance

    zone0.25

    0.01

    Produced part

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    IE 316 Manufacturing

    Engineering I - Processes

    Surface Integrity

    Surface texture alone does not completelydescribe a surface

    There may be metallurgical changes in the altered

    layer beneath the surface that can have asignificant effect on a material's mechanicalproperties

    Surface integrityis the study and control of this

    subsurface layer and the changes in it that occurduring processing which may influence theperformance of the finished part or product

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    IE 316 Manufacturing

    Engineering I - Processes

    Surface Changes Caused by Processing

    Surface changes are caused by the applicationof various forms of energy during processing

    Example: Mechanical energy is the most common

    form in manufacturing. Processes include metalforming (e.g., forging, extrusion), pressworking,and machining

    Although primary function is to change geometry

    of workpart, mechanical energy can also causeresidual stresses, work hardening, and cracks inthe surface layers

    Surface Changes Caused by

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    IE 316 Manufacturing

    Engineering I - Processes

    Surface Changes Caused by

    Mechanical Energy

    Residual stresses in subsurface layer

    Cracks - microscopic and macroscopic

    Laps, folds, or seams

    Voids or inclusions introduced mechanically

    Hardness variations (e.g., work hardening)

    Surface Changes Caused by

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    IE 316 Manufacturing

    Engineering I - Processes

    Surface Changes Caused by

    Thermal Energy

    Metallurgical changes (recrystallization, grain

    size changes, phase changes at surface)

    Redeposited or resolidified material (e.g.,

    welding or casting)

    Heat-affected zone in welding (includes some

    of the metallurgical changes listed above)

    Hardness changes

    Surface Changes Caused by

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    IE 316 Manufacturing

    Engineering I - Processes

    Surface Changes Caused by

    Chemical Energy

    Intergranular attack

    Chemical contamination

    Absorption of certain elements such as H and

    Cl in metal surface

    Corrosion, pitting, and etching

    Dissolving of microconstituents

    Alloy depletion and resulting hardness

    changes

    Surface Changes Caused by

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    IE 316 Manufacturing

    Engineering I - Processes

    Surface Changes Caused by

    Electrical Energy

    Changes in conductivity and/or magnetism

    Craters resulting from short circuits during

    certain electrical processing techniques

    Tolerances and Manufacturing

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    IE 316 Manufacturing

    Engineering I - Processes

    Tolerances and Manufacturing

    Processes

    Some manufacturing processes are inherently

    more accurate than others

    Examples:

    Most machining processes are quite accurate,

    capable of tolerances = 0.05 mm ( 0.002 in.) or

    better

    Sand castings are generally inaccurate, andtolerances of 10 to 20 times those used for

    machined parts must be specified

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    Surfaces and Manufacturing Processes

    Some processes are inherently capable of

    producing better surfaces than others

    In general, processing cost increases with

    improvement in surface finish because additionaloperations and more time are usually required to

    obtain increasingly better surfaces

    Processes noted for providing superior finishes

    include honing, lapping, polishing, and

    superfinishing