REVI EW OF I NDI AN STANDARDS I S:9609 English let t er ing f or t echnical dr awings. I S:10711 Sizes of dr awing sheet s. I S:10712 Pr esent at ion of it em r ef er ences on t echnical dr awings. I S:10713 Scales f or use in t echnical dr awings. I S:10714 Gener al pr inciples of pr esent at ion on t echnical dr awings. I S:10715 Pr esent at ion of t hr eaded par t s on t echnical dr awings. I S:10716 Rules f or r epr esent at ion of spr ings on t echnical dr awings. I S:10717 Convent ional r epr esent at ion of gear s on t echnical dr awings. I S:10718 Met hod of dimensioning and t oler ancing cones on t echnical dr awings. I S:10719 Met hod of indicat ing sur f ace t ext ur e on t echnical dr awings. I S 10720 Technical dr awings f or st r uct ur al met al wor ks. I S:11663 Convent ional r epr esent at ion of common f eat ur es and mat er ials on t echnical dr awings. I S:11669 Gener al pr inciples of dimensioning on t echnical dr awings.

OTHER I NDI AN STANDARDS

I S:919 (2 par t s) I S:2102(2 par t s) I S:2709 I S:8000(4 par t s)

I S:3073 I S:4218 (6 par t s)

I SO syst em of limit s and f it s. Gener al t oler ances. Guide f or select ion of f it s. Toler ances of f or m and posit ion f or engineer ing dr awings. Assessment of sur f ace r oughness. I SO Met r ic scr ew t hr eads

RECOMMENDED SCALES Full Scale 1:1 Reduced Scale 1:2 1:2.5 1:5 1:10 1:20 1:50 1:100 1:200 Enlarged Scale 10:1 5:1 2:1

Proj ect ions The symbol is indicated on the drawing clearly in the title block.

Symbol for first angle projection

Symbol for third angle projection

Dimensioning on Engg. Drgs. Dimensions shall be given f r om visible out lines r at her

t han f r om hidden lines.

Dimensioning on Engg. Drgs.I t is pr ef er able t o give dimensions f r om a base line or a cent r e line of a hole or a cylindr ical par t .

Dimensioning . . . .

Cont d. .

Dimensioning t o a cent er line shall be avoided except

when t he cent er line passes t hr ough t he cent r e of a hole or a cylindr ical par t .

Dimensioning . . . .

Cont d. .

Dimension lines and pr oj ect ion lines ar e dr awn as cont inuous t hin lines. Pr oj ect ion lines should ext end slight ly beyond t he dimension line.

Dimensioning . . . .

Cont d. .

Const r uct ion and int er sect ing pr oj ect ion lines should ext end slight ly beyond t he point of int er sect ion.

Dimensioning . . . .

Cont d. .

Leader s which t ouch t he lines shall not be nor mally inclined less t han 30 o angle. Should not be par allel t o t he adj acent dimension or pr oj ect ion line. Use of common leader should be avoided.

Dimensioning . . . .

Cont d. .

Use of common leader should be avoided.

Dimensioning Arrows

I nscript ion of dimensions

The diamet er symbol is used, bef or e a dimension t o indicat e t he diamet er . The let t er R is used, bef or e a dimension t o indicat e a r adius. The let t er SQ is used, bef or e a dimension t o indicat e a squar e. The let t er HEX is used, t o indicat e a hexagon bef or e acr oss dimension. The wor d SPHERE is used, t o indicat e a spher ical sur f ace bef or e t he r adius or diamet er dimension.

Addit ion of let t ers and symbols

Addit ion of let t ers and symbols

The diameter symbol is used, before a dimension to indicate the diameter. The letter R is used, before a dimension to indicate a radius. The letter SQ is used, before a dimension to indicate a square. The letter HEX is used, to indicate a hexagon before across dimension. The word SPHERE is used, to indicate a spherical surface before the radius or diameter dimension.

Special indicat ions To indicate a surface or a surface zone to give an additional treatment which shall be applied within limits to be specified on the drawing.

Arrangement of dimensionsChain dimensioning

Parallel dimensioning

Combined dimensioning

Dimensioning by coordinat es

Superimposed running dimensioning

Equidistant features

Equal dimensions

Assembled parts

The tolerance value restricted to the specified length.

ANGULAR DI MENSI ONS

DI MENSI ONI NG OF KEY WAYS & TAPERS

TOLERANCES FOR LI NEAR AND ANGULAR DI MENSI ONS WI THOUT I NDI VI DUAL TOLERANCE I NDI CATI ONS

I NDI CATI ONS ON THE DRAWI NGSGENERAL TOLERANCES FOR LINEAR DIMENSIONS ARE AS FOLLOWS.

Designat ion f m c v

Descript ion f ine medium course course very

I NDI CATI ONS ON THE DRAWI NGSGeneral tolerances about the untoleranced dimensions to be given near the title block in the drawing. Ex: untoleranced dimensions as per : IS 2102 medium.

Permissible deviations for linear dimensionsPermissible deviat ions f or basic size rangeDesignat ion Descript ion

0.5 0.3

Over 36

Over 6 - 30

Over 30 - 120

Over 120-400

Over 400-1000

Over 1000-2000

Over 2000-4000

f m c v

f ine medium course very course

0.05 0.1 0.2 -

0.05

0.1 0.2 0.5 1

0.15 0.3 0.8 1.5

0.2 0.5 1.2 2.5

0.3 0.8 2 4

0.5 1.2 3 6

2 4 8

0.1 0.3 0.5

For nominal sizes below 0.5mm, the deviations shall be indicated adjacent to the relevant nominal size (s)

GENERAL TOLERANCES FOR RADI I AND CHAMFER HEI GHTS

Permissible deviat ions f or basic size rangeDesignat io Descript ion n f ine0.5 - 3 Over 3 6 Over 6

f m c v

medium course very course

0.2 0.4

0.5 1

1 2

For nominal sizes below 0.5mm, the deviations shall be indicated adjacent to the relevant nominal size (s)

ANGULAR DI MENSI ONS

Permissible deviat ions f or basic size rangeDesignat io Descript ion nUpto 10 Over 10-50 Over 50-120 Over 120-400 Over 400

f m c v

f ine medium course very course

1o 1o30 3o

0o30 1o 2o

0o20 0o30 1o

0o10 0o15 0o30

0o5 0o10 0o20

TOLERANCE DI SPOSI TI ON CHART

Accur acy expect ed of manuf act ur ing pr ocess

SURFACE ROUGHNESS

Sur f ace t ext ur e on dr awingSymbols for surface textureThe basic symbol consists of two legs of unequal length inclined at approximately 60o to the line representing the considered surface If the removal of material by machining is required, bar is added to the basic symbol

If the removal of material is not permitted, a circle is added to the basic symbol. When a special charecteristics have to be indicated a line is added to the longer arm of the symbol,

SURFACE ROUGHNESS The value of the machining allowance shall be indicated on the left of the symbol. Surface texture shall be placed relative to the symbol.

or cut-off length

I ndicat ion of surf ace roughness on drawingSurface roughness is normally indicated on the drawing by the symbols

, , , , .The surface as represented by the symbol Symbol represented by the symbol .

is finer than the surface as

indicates un machined surface.

Surface roughness represented by symbols machining such as turning and milling, etc. Surface roughness represented by operation.

and can be achieved bycan be achieved by grinding

Surface represented by the symbol can be achieved by fine grinding, super finishing, lapping and honing operation.

I ndicat ion of sur f ace r oughness on dr awing

Syst em of assessment of surf ace roughness

Maximum peak to valley value (Rmax)

The distance between the two parallel lines. i.e. one through the maximum point and the other through the minimum point of the profile

Surface roughness value ( Rz )

The value obtained by this method is indicated as Rz from which Ra is evaluated. Rz = [(R1 + R3 + R5 + R7 + R9) ( R2 + R4 + R6 + R8 + R10)] / 5 Calculated values of Ra and Rz : Log Rz = 0.65 + 0.97 log Ra

The Ten Point Height Method is used for determining surface roughness values on the basis of graphical records of the profile

An empirical relation is Rz = K. Ra Where K is a constant varying from 3.9 for rough surface to 5 for fine surfaces. In practice Rz: Ra = 4, can be adopted.

Centre line average value (C.L.A. value) Ra

This system measures the average of 5 to 10 values to assess the roughness value. The reference line for measurement is the mean line of the profile, which divides the actual profile of the surface in such a way that the total of the areas above the line and the profile is equal to the total of the area below the line and the profile. The C.L.A. value denoted by the symbol Ra It is expressed in microns = 10 6 of a meter. Ra = (Y1 + Y2 + Y3 + .. + Yn) / n = 6Yn / n Y1, Y2, Y3, .Yn are added irrespective of their sign

Root mean square value (Rrms)

The value of roughness is obtained from the profile record of the surface and is defined as the average root mean square deviation (Y) of the profile from its mean line in a definite sampling length (L) Ra and Rrms are roughly proportional. Rrms = [(6Y2n ) / n] Rrms value about 10% greater than Ra.

m

(5572/13) x (1/10) = 2.07 Pm

Qualit y of scraped surf acesDetermined by the number of contact surfaces between the scraped surface and inspection surface in an area of 25 mm x 25mm square. Scraped surfaces are divided into 5 classes: The size of the surface plate used for the measurement must be proportional to the Surface roughness of the machined surface before scrapping must not be coarser than Ra = 3.2 Pm. size of the scraped surfaces. From most precise to most coarse.

Symbols f or t he dir ect ion of lay

I ndicat ions on dr awing A basic symbol (in brackets) of the special surface texture or textures. The symbol or symbols (in brackets) of the special surface texture of textures.

The symbols for the surface textures which are exceptional to the general symbol are indicated on the corresponding surfaces.

TAYLOR HOBSONS SURTRONI C

Measur ement s wit h dif f er ent syst ems of st ylus

THREADS TOLERANCI NG SYSTEM

ELEMENTS OF THREADS

Formulae used

Toler ance gr ades f or t hr eadsMALE (BOLT) GRADESPITCH DIAMETER

FEMALE (NUT) GRADES

3,4,5,6,7,8,9 4,6,8NOT APPLICABLE

4,5,6,7,8NOT APPLICABLE

MAJOR DIAMETER

MINOR DIAMETER

4,5,6,7,8

Fundament al Deviat ionsMALE (BOLT) DEVIATIONS FEMALE (NUT) DEVIATIONS

e, g, h

G, H

The amount of displacement for various deviations depends upon the pitch

Recommended t hread t olerances f or bolt s & nut s BOLTS Fine Medium (commercial type) Coarse 4h 6g 8g NUTS 5H 6H 7H

General applicat ionFor precision and fine pitches For commercial purpose, Class 3,4 & 5 Class 6

For long thread lengths, hot rolled, blind threads Class 7, 8 & 9

GEOMETRI CAL TOLERANCI NG

DEFI NI TI ON A geometrical tolerance is the maximum permissible variation of Form Orientation Location of a feature

POI NTS, LI NES AND SURFACES

Points have position, but no size. Joining of points is a line, it can be a straight line or a curved line. Surfaces are composed of lines.

FEATURE CONTROL SYMBOLS

LENGTH AS REQUIRED

Feature is a specific characteristic portion of a part. Point, line, surface, hole, slot, screw thread or profile. The frame height to be twice the height of the character used for dimensioning, tolerancing and notes on the drawing.

POSI TI ON OF ARROW HEAD On the outline of the feature

On an extension of the out line

On an extension (projection) line from the feature, in line with the size dimension.

POSI TI ON OF ARROW HEAD Geometrical tolerance with reference to center line.

The feature control symbol is shown in association with the size dimension.

APPLI CATI ON TO SURFACES

The leader and arrowhead should be from the feature control symbol. Usually perpendicular to the line or surface. Or at an angle.

Two or more feature control symbols, which apply to the same feature, are drawn together with a single leader and arrowhead

APPLI CATI ON TO CENTER LI NES

Used for multiple diameter parts with a common axis.

APPLI CATI ON TO CENTER LI NES CONTROL OF CENTER LINE OF A PORTION OF A PART

FORM TOLERANCI NG STRAI GHTNESS OF LI NES & SURFACES

STRAIGHTNESS SYMBOL

STRAI GHTNESSDEFINITION:

Straightness is a condition where an element of a surface or an edge is in a straight line.

Typically used to control the form of cylindrical or conical surfaces. The straightness requirement applies to the entire surface.

TYPICAL USE:

STRAI GHTNESS

Straightness tolerance is specified on a drawing by means of a feature control symbol, which is directed by a leader to the line requiring control.

I NTERPRETATI ON

0.05

The lines should be straight within 0.05 mm.

This means that the line should be contained within a tolerance zone consisting of the area between two parallel straight lines in the same plane, separated by the specified tolerance.

STRAI GHTNESS

STRAIGHTNESS CHECKING WITH A STRAIGHT EDGE

MEASURING Straightness can be measured by bringing a straight edge in contact with the line, and determining the space between the straight edge and the line.

MEASURI NGStraightness includes all errors of form, such as concavity, convexity, waviness, tool marks and other such imperfections.

If the feature tends towards convexity the height of the tolerance zone is measured where the least possible straightness error results.

STRAI GHTNESSON CYLINDRICAL SURFACES

STRAIGHTNES ERRORS IN A CYLINDRICAL SURFACE

STRAI GHTNESSON PROFILED SURFACES A straight tolerance when applied to the surface, controls surface elements only. It controls bending or a wavy condition of the surface, or a barrel shaped part. Straightness not necessarily control the straightness of the centerline, nor conicity of the cylinder.

STRAI GHTNESS

MEASUREMENT OF STRAIGHTNESS

MEASURING PRINCIPLEThe part is set up by suitable means, such as V-blocks on a surface plate, with the surface to be evaluated closely parallel to the plate. Readings are then taken at various points along the surface.

STRAI GHTNESS

INTERPRETATION Each line element of the surface shall be contained with in a tolerance zone consisting of the space between two parallel planes, separated by the width of the specified tolerance, when the part is rolled along one of the planes.

STRAI GHTNESSON CONICAL SURFACES

STRAI GHTNESSON FLAT SURFACES

A straightness tolerance indicates in one direction only.

STRAI GHTNESS

FLAT SURFACES The straightness tolerances may all be shown on a single view by indicating the direction with short lines terminated by arrow heads.

STRAI GHTNESS

MEASURING PRINCIPLE Straightness of a flat surface could be checked by laying a straightedge along the part, and measuring any resultant space.

STRAI GHTNESSON REGULAR POLYGONS

Straightness tolerance applies to all of the longitudinal surfaces. For all other shapes it applies only to those surfaces indicated unless otherwise specified.

STRAI GHTNESSSTRAIGHTNESS IN A SPECIFIED LENGTH

The expression 0.2/50 does not mean 0.2mm per 50mm of length. It means 0.2 mm in any 50mm long portion of the part.

Indicates straightness within 0.2mm for the full length. Not to exceed 0.05mm in any 25mm length.

STRAI GHTNESS OF FEATURES OF SI ZEAPPLICATION The same straightness symbol is used in the feature control symbol as for straightness of surface elements. However, when not modified by MMC, the feature control symbol may be directed either to the center line, or to extension lines from the diameter or thickness as shown.

APPLI CATI ON

Unless it is perfectly clear as to whether it refers to the lengthwise or widthwise Straightness. If the cross section is circular the tolerance zone becomes circular and a diameter symbol then precedes the tolerance

Positioning the feature control symbol between the views should be avoided.

I NTERPRETATI ON

A straightness tolerance applied to a center line means that all centerlines between opposing line elements of the surface shall lie completely within tolerance zones having a width equal to the specified tolerance

MEASURING PRINCIPLE The part to be measured is mounted using some suitable means of support, such as between centers or on V blocks. Two indicators are mounted diametrically opposite one another, preferably on the same carriage and arranged to move parallel to the centerline being measured as shown. Indicators are placed at zero at one end and differences in readings between the two indicators are noted as the carriage is moved toward the other end.

STRAI GHTNESS

If a centerline is common to two or more diameters of other features, a straightness tolerance directed to the centerline applies to all features on the common centerline unless otherwise specified

STRAI GHTNESS OF ONE FEATURE OF MULTI PLE DI AMETER PART

If the tolerance is intended to apply to only one thickness or diameter on the common center line, a note may be added beneath the feature control symbol . Alternatively the symbol may be directed to extension lines from the surfaces.

DI RECTI ON OF APPLI CATI ON OF STRAI GHTNESS Straightness of a center line or median plane applies only to center lines which run in the direction of the line or line elements to which the straightness tolerance is directed. The width or diameter of the tolerance zone lies in the direction in which the arrowhead points. In the rectangular part in Fig., the control applies only to longitudinal centerlines between corresponding line elements of the top and bottom surfaces. If the cross section is circular or is a regular polygon, with no means of determining a specific orientation for measuring purposes, the tolerance applies in all applicable directions, as already explained.

If there is a ready means of identifying the orientation, the tolerance applies only in the direction indicated . If there may be some ambiguity a note should be added, such as THIS DIRECTION ONLY . If the part is circular and it is intended that the tolerance apply in all directions a diameter symbol should precede the tolerance value.

If a tolerance is shown in two directions it is measured in these two directions and the tolerance zone is then a parallelopiped

STRAI GHTNESS MAXI MUM MATERI AL CONDI TI ON It actually specifies a virtual size, equal to the maximum material limit of size plus or minus the specified geometrical tolerance

To signify that the maximum material principle the symbol (M) is placed immediately after the tolerance value in the feature control symbol As there must always be a feature size dimension associated with such a tolerance it is useful and convenient to establish this relationship by directing the feature control symbol in line with the dimension, or associating it with the dimension by a common leader

STRAI GHTNESS MAXI MUM MATERI AL CONDI TI ON

Tolerance of zero MMC, means that the virtual size limit coincides with the maximum material limit. If a feature is everywhere at its maximum material limit of size, no errors of straightness are permitted.

STRAI GHTNESS MAXI MUM MATERI AL CONDI TI ON

A straightness tolerance modified by (M) means that the feature should lie within a tolerance zone consisting of the line between two parallel lines, in the same plane as the longitudinal section of the feature being evaluated. These zone lines are separated by the special straightness tolerance, plus the maximum material size of feature

MEASURI NG PRI NCI PLE

Gage consists of two straight and parallel gauging elements between which the part must pass. These gauging elements must be at least as along as the length of the feature being gauged. The gage must be maintained normal to the surface being evaluated.

STRAI GHTNESS OF I NTERNAL FEATURES

This is because such features are more readily controlled by other geometrical tolerances, such as cylindricity, perpendicularity, or position, all of which control straightness. However straightness is very useful control for some internal features, such as grooves and slots.

It is very seldom used for round holes.

STRAI GHTNESS WI TH A MAXI MUM VALUE

If it is desired to ensure that the straightness error does not become too great when the part approaches the least material size limit, a maximum value may be added, as shown.

FORM TOLERANCI NG - FLATNESSFLATNESS SYMBOL

FORM TOLERANCI NG - FLATNESS

FLATNESS OF A SURFACE

The condition of a surface having all elements in one plane.INTERPRETATION

The flatness tolerance specifies a tolerance zone defined by two parallel planes within which the surface must lie.

CONTROLLI NG FLATNESS ON TWO OR MORE SURFACES

If the same control is desired on two or more surfaces a suitable note may be added instead of repeating the symbol

FORM TOLERANCI NG - FLATNESS

MEASURING PRINCIPLEThe part of be measured is set up on a surface plate or measuring plane, using one fixed An indicator gage is set to zero on the area above the fixed support. and two adjustable supports spaced as far apart as possible.

The other supports are adjusted to give zero readings above each support. tolerance is not exceeded.

Readings are then taken at a sufficient number of points on the surface to ensure that the

CONTROL OF DI RECTI ON OF ERRORS

It is sometimes desired to further control the direction of flatness errors, for which purpose a note may be added beneath the feature control symbol, such as MUST NOT BE CONCAVE or MUST NOT BE CONVEX

FORM TOLERANCI NG - FLATNESS

SYMBOL & APPLI CATI ON

The symbol is the same as for flatness of a surface, except that the modifier (M) is placed after the tolerance value, and the feature control symbol is directed to the thickness dimension

FLATNESS MMC BASI SA flatness tolerance on an MMC basis means that the feature or part shall be contained within a tolerance zone consisting of the space between two parallel planes, which are separated by the specified tolerance plus the maximum material size

These planes must be large enough to completely encompass the feature Flatness on an MMC basis is a very useful tool as a control for relatively thin parts, which may be subjected to bending or dishing

FORM TOLERANCI NG - FLATNESSFLATNESS MMC BASIS MEASURING PRINCIPLE

On an MMC basis, the measurement of flatness requires the use of a functional GO gage. The gage consists of two parallel plane surfaces, large enough to encompass the whole part, and between which the part must pass

FORM TOLERANCI NG - FLATNESSFLATNESS FOR A SPECIFIED LENGTH

If flatness within a specified length is given the gage must be made of this length

ROUNDNESS

RoundnessRoundness refers to a condition of a circular line or the surface of a circular feature wherein all points on the line or on the periphery of a plane cross section of the feature, are equidistant from a common center point .Examples : Disc, Sphere , Cylinder, Cone

Errors of Roundness

Errors of Roundness

Ovality : Difference appear in major and minor axes.

Errors of Roundness

Lobing: Small Variation in diameter as shown in figure.

Errors of Roundness

Irregularity : Random irregularities from a true Circles

ROUNDNESS SYMBOLThe geometrical characteristic symbol for roundness is simply a circle, having a diameter 75% of the feature control symbol frame height.

ROUNDNESS SYMBOL

ROUNDNESS TOLERANCE

The var iat ion should lie wit hin t he widt h of t he Annular space bet ween t wo concent r ic cir cles

ROUNDNESS TOLERANCE

Incorrect

Incorrect

Correct

Roundness error is min. radial separation between two concentric circles within which all points on measured surface to lie.

ROUNDNESS ERROR MAY EXCEEDS SI ZE BOUNDARY

Measurements between any two opposing points along the circumference shall be within the specified diameter tolerance limits. The outer diameter of the roundness tolerance zone exceeds the actual measured diameter of the part by the amount of roundness tolerance.

ROUNDNESS OF CYLI NDERS AND SPHERES

ROUNDNESS FOR A CYLINDRICAL FEATURE

INTERPRETATION OF ROUNDNESS TOLERANCE

It is preferable to direct a roundness tolerance for a cylindrical feature to the view in which the feature appears as a circle. The tolerance applies to all planes perpendicular to the axis.

ROUNDNESS TOLERANCE APPLI ED TO A SPHERE

The tolerance is shown in the same manner and applies to any or all planes, which pass through a section of maximum diameter.

ROUNDNESS OF NON- CYLI NDRI CAL PARTS

Non-cylindrical parts refer to conical parts and other features which are circular in cross-section but which have variable diameters. Since many sizes of circles may be involved it is usually best to direct the roundness tolerance to the longitudinal surface as shown.

ROUNDNESS MEASURI NG PRI NCI PLE

The measurement of roundness presents some problems, as it does not lend itself to direct measurement. Indirect measurement involves establishing the relationship of the periphery of a feature with the geometry of a perfectly round form, regardless of its size or the exact position of its center. It is immaterial whether the part is revolved in contact with a fixed indicator or whether the indicator is revolved around the part.

POLAR CHART & TRANSPARENT OVERLAY CHART

POLAR CHART

PROFILE OF PART

TRANSPARENT OVERLAY CHART

The indicator readings are entered directly on polar chart during roundness measurement of cylinder. The profile is evaluated by means of transparent overlay chart on which concentric circles are scribed to the same scale as the polar chart.

Note : There are a number of commercial instruments available, based on optical, mechanical, or electronic principles, some of which produce a polar chart automatically as the part is revolved

ALTERNATI VE MEASURI NG PROCEDURES

It is sometimes suggested that parts be checked for roundness by revolving them in suitable V-block, while measuring the upper surface with an indicator gage This method does not measure in accordance with the definition of roundness, and is therefore not recommended for precise results.

(NOT) RECOMMENDED

ALTERNATI VE MEASURI NG PROCEDURES An estimate of out of roundness errors can sometimes be obtained by making separate measurements on a part in V-blocks having different included angles, for example 180q, 120q, 90q and 60q. If all measurements show little or no indicator movement it might be assumed that the part is satisfactory. Full indicator reading is approximately equal to measurement over a diameter, instead of a radius. The roundness error will therefore be roughly half the indicator movement.

(NOT) RECOMMENDED

ALTERNATI VE MEASURI NG PROCEDURES

USE OF TWO BLOCKS

To avoid errors of readings due to bending of the parts it may be necessary to employ two narrow vee-blocks. In this method one of the vee-blocks must always be directly under the point of measurement.

ALTERNATI VE MEASURI NG PROCEDURES

HOW LOBING CAUSES ERRORS IN MEASURING

V-blocks (not)recommend -Reasons Five Lobed part in 60q V-block-- indictor reading practically zero even though the component is out of round

ALTERNATI VE MEASURI NG PROCEDURES

V-blocks (not)recommend -Reasons Three Lobed part in 60q V-block-- indictor reading greatly exaggerated for small variation of roundness.

ROUNDNESS OF I NTERNAL DI AMETERS

(NOT RECOMMENDED) ROUNDNESS OF INTERNAL DIAMETERS

Round holes can be toleranced for roundness in the same manner as external cylindrical features, If the holes are large enough for insertion of a gaging probe, similar methods used for external measurement can be used. Indicator gauges used for measurement of internal roundness for bigger hole diameters. Drawback of this method is same as that of V-blocks For small holes, where suitable gaging probes or indicators cannot be used, it is recommended that roundness tolerances be replaced by cylindricity tolerances of zero MMC

ROUNDNESS ON MMC BASI S

It is often desirable to ensure that any errors of roundness do not cause the periphery of the feature to cross the maximum material boundary. This shall ensure that the part will assemble satisfactorily with its mating part. This is accomplished by specifying a roundness tolerance on an MMC basis. A tolerance on this basis is generally directed to the diametric dimension, such as the zero MMC tolerance.

ROUNDNESS ON AN MMC BASI S

ROUNDNESS TOLERANCE ON MMC BASIS

Max. Dia. of Tolerance Zone Min. Dia. of Part Minor Dia. of Tolerance Zone Mean Tolerance Zone

= 50.00mm = 49.88mm = 49.76mm = 0.12mm

PART MAY CROSS THE LEAST MATERIAL BOUNDARY

CYLI NDRI CI TY

Cylindricit yCylindricity refers to a condition of a surface, which forms a cylinder where the surface elements in cross sections parallel to the axis are straight and parallel and in cross sections perpendicular to the axis are round. Cylindricity thus combines in one term geometrical form tolerances for roundness, straightness and parallelism of the surface elements.

Cylindricit yCylindricity tolerances can only be applied to cylindrical surface, such as round holes and shafts. No specific geometrical tolerances have been devised for other circular forms, which require the use of several geometrical tolerances. A conical surface, for example, must be controlled by a combination of tolerances for roundness, straightness, and angularity.

Cylindricit yErrors of Cylindricity may be caused by out of roundness, like ovality or lobing Errors of straightness caused by bending or by diametral variation Errors of parallelism like conicity or taper Random irregularities from a true cylindrical form.

CYLI NDRI CI TY SYMBOL

Th e ge o m e tric ch ara cte ris tic s ym bo l fo r cylin d ricity co n s is ts o f a circle w ith tw o tan ge n t lin e s at 6 0 q. co n tro l s ym bo l fra m e . Th e circle d iam e te r is 6 2 % o f th e h e igh t o f th e fe a tu re

CYLI NDRI CI TY TOLERANCE

CYLINDRICITY TOLERANCE DIRECTED TO EITHER VIEW.

The Cylindricit y t olerance symbol is used in a f eat ure cont rol symbol Direct ed t o t he cylindrical surf ace, in eit her t he side view or end view

CYLI NDRI CI TY TOLERANCE

A Cylindricit y t olerance specif ies a t olerance zone consist ing of t he annular space bet ween t wo coaxial cylinders, having a dif f erence in radii equal t o t he specif ied t olerance zone of 0. 05 on radial dimension.

PERMISSIBLE FORM ERRORS

CYLI NDRI CI TY TOLERANCE

DIAMETER OF THE TOLERANCE ZONE MAY BE LARGER THAN MAXIMUM DIAMETER OF THE PART

When t he par t is at t he maximum diamet er limit t he maj or diamet er of t he Cylindr icit y t oler ance zone would likely be lar ger t han t he maximum diamet er limit .This may be due t o lobing, and ot her ir r egular it ies or bending.

MEASURI NG METHODS

PART IN VEE BLOCKS FOR CYLINDRICITY TESTS

Checked by revolving in vee-blocks while taking indicator readings on the top surface, in a manner similar to methods described for the measurement of roundness The roundness near both ends is first checked by making indicator readings directly over blocks of varying angles to ensure that lobing will not significantly affect the results. The part is then mounted in identical short length vee-blocks, which are located at each end of the part

CYLI NDRI CI TY OF HOLESCylindricity tolerances are applicable to internal cylindrical surfaces, such as round holes. Measurement Large holes can be assessed by means of indicator or electronic gauges. Best method is to assess the holes with a plane round GO gauge of length at least equal to the full length or depth of the hole and having the diameter equal to the max. material size minus the specified tolerance

Coplanarit y and Symmet ry

CORRELATI VE TOLERANCI NG Correlative geometrical tolerancing refers to tolerancing for the control of two or more features, intended to be correlated in position or attitude.

It refers to the relative position of two or more flat surfaces, which are intended to lie in the same geometrical plane. No special symbol exists for co planarity. Either the symbol for position or the symbol for flatness may be used, depending on the type of control required. Fig illustrates a suitable method of tolerancing when one or more surfaces are required to be coplanar with a principal surface, which is then specified as a datum feature. The tolerance controls orientation and flatness of the toleranced surfaces within the same limits. But does not control flatness of the datum feature surface. The position of the surfaces in relation to the base or other features of the part must be separately dimensioned and toleranced, as shown by the 25mm dimension.

COPLANARI TY

Application: In Fig, Coplanar surfaces are also required to be accurately located and parallel to another surface of a part, which is then designated as a datum feature. In this case, the datum and the controlled surfaces must be associated by a basic dimension.Although the positional tolerance applies separately to each surface, the tolerance zones are of equal width, and are each parallel to and at equal distances from the datum surface. This condition results essentially in one tolerance zone within which the surfaces must lie simultaneously. The positional tolerance controls orientation and form (parallelism and flatness) of both surfaces within the same limits.

It is sometimes necessary to reference surfaces to a datum system instead of to a single datum surface. This occurs when it is necessary to control coplanar surfaces perpendicular to a datum instead of parallel to it. Fig shows a case where the coplanar surfaces are required to be perpendicular to the axis of a hole.

B

SI MULTANEOUS REQUI REMENTS If it is necessary to hold co planarity of two or more surfaces within close limits but permit a greater variation in the position of the surfaces in relation to other features of the part, two methods of tolerancing may be used. Both give the same results.

1

2

The surfaces may be positioned relative to one another, using the symbol for position, as shown in the Fig 1. Alternatively they may be treated as one flat surface, using a flatness tolerance and symbol as shown in the Fig 2. The word SIMULTANEOUS must be added beneath the feature control symbol. Otherwise the tolerance would apply separately to each surface, and would control their flatness but would not ensure that they were in the same plane. A profile symbol may also be used instead of flatness symbol.

A parallelism tolerance is sometimes used for coplanar surfaces, as shown in Fig. Such a tolerance only controls parallelism and flatness of the surfaces. Their positions may vary anywhere within the tolerance zone for position specified by the toleranced dimension.

OTHER CORRELATED SURFACES Many features other than flat surfaces may be correlated if they have line elements in a single direction in the same straight or circular line. It is often possible to control such features using controls similar to those applied to coplanar surfaces. Either a positional tolerance or a simultaneous form tolerance may be used, depending on the type of control required. Fig below, gives a few examples.

SYMMETRYDEFINITION Symmetry is a condition in which a feature or features are symmetrically disposed about a centerline or center plane of another feature. The centerline or plane of the second feature is usually specified as a datum. A symmetry tolerance specifies the width of a tolerance zone. This width is the area between two parallel lines or the space between two parallel planes equally disposed about the datum axis or median plane. Symmetry is therefore a special case of position. The advantage of using the symmetry symbol rather than the position symbol is that it indicates that the true position is symmetrical and often eliminates the need for basic dimensions to correlate the position of features.

SYMMETRYSYMBOL The geometric characteristic symbol for symmetry consists of three horizontal lines, as shown in Fig. The dimensions refer to percentages of the feature control symbol frame height.60 %

SYMMETRY APPLI CATI ONS RFS

Fig shows a simple example in which a slot is intended to be symmetrical with the overall width of the part, which in turn is specified as the datum. Note that it is not necessary to show a true position dimension for the slot or equal dimensions from the sides of the slot to the sides of the part, which might be deemed necessary if a positional tolerance, were used.

The interpretation, shown in Fig below, shows the tolerance zone equally disposed about the centerline or median plane of the datum feature. Theoretically this centerline or median plane of the datum feature is perfectly straight and true, being based only on the high spots of the feature resting on the datum surfaces. The centerline of each controlled feature is influenced by any errors of form or orientation of the surfaces. However, the width of the tolerance zone remains the same for each part, regardless of the actual size of the feature or of the datum feature.

Example 1

MEASURI NG PRI NCI PLE

One surface of the datum feature is laid directly on a surface plate, as shown in Fig. Measurements are made from the datum surface to one side of the slot. The highest and lowest readings are noted. The part is then revolved 180, so that the other surface of the datum feature rests on the surface plate and measurements are made to the other surface of the slot. The difference between the highest and lowest of all of the measurements constitutes the symmetry error, which must not exceed the specified tolerance.

Example - 2

The Fig above shows with two slots, one of which is designated as a datum feature. For measuring purpose the part is supported on one side of the datum slot while the measurements are made to the other slot.

MEASURI NG PRI NCI PLE OF SYMMETRYExample - 3

Fig.1 shows a part in which a hole is required to be symmetrical with the sides of the part as well as perpendicular to the face of the part.

1

2

MEASURI NG PRI NCI PLE OF SYMMETRYExample 3 cont. Measurement can be made, by fitting the hole with a close fitting mandrel and supporting the part against an angle plate, representing datum A, as shown in Fig.1. The part must also touch the surface plate along its length. The height is then measured from the surface plate over the mandrel. Readings are taken at two points on the mandrel, separated by a distance W, equal to the width of the part, as shown in Fig.2. Height measurements for the hole are then calculated from the formulae shown below, paying particular attention to the mathematical signs in each case. For example, if E is larger than F, (F-E) becomes a negative quantity, and the second formula becomes D=C (E-F). The part is then revolved 180 and measurements repeated with surface resting on the surface plate. The maximum difference between any of the four measurements represents the symmetry error.

1 2

Example - 4

Symmetry can also be applied to parts with circular datums as shown in the Fig above. For measuring purpose the small hole is fitted with a suitable mandrel. Measurements are then made between the mandrel and the sides of the datum hole, such as by inserting gage pins as shown in Fig. The difference between the sizes B&C gives the symmetric error. This measurement shall be precise only if the datum hole has no roundness errors, which might increase and decrease the apparent symmetry error

APPLI CATI ON ON AN MMC BASI S When ever possible symmetry should be specified on an MMC basis. Such specification solves most of the measurement problems by permitting use of suitable functional GO gages. Some examples of parts toleranced on this basis, with suitable gaging principles, are shown below.

6.0

Exam ple 1

5.95

6.0 s

6.0 s

Exam ple 2

6.0 s

Exam ple 3

Exam ple 4

Exam ple 5

Exam ple 6

Concent ricit y And Coaxialit y

CONCENTRI CI TY AND COAXI ALI TY Concentricity is a condition in which two or more features, such as circles, spheres, cylinders, cones, or hexagons, share a common center or axis. An example would be a round hole through the center of a cylindrical part. Coaxiality is a very similar condition in which two or more circular or similar features are arranged with their axes in the same straight line. Examples might be a counter bored hole or a shaft having parts along itslength turned to different diameters. Both these terms are often used interchangeably. For geometrical

tolerancing the same symbol is used for both conditions.

SYMBOL The geometric characteristic symbol for both concentricity and coaxiality consists of two concentric circles, having diameters equal to 75% and 50% respectively of the feature control symbol frame height

CONCENTRICITY SYMBOL

CONCENTRI CI TY TOLERANCI NG

CONCENTRICITY OF CIRCLES

D iam e te r A is th e D atu m Circle Co n ce n tricity To le ran ce is applie d to th e o u te r circle Th e Circle w ith 0 .12 D ia. is th e to le ran ce zo n e

ENLARGED PROFI LE OF PART

The datum center is the center of the largest perfect circle, which can be inscribed within the datum feature. The center points of the controlled circle are established from the periphery of the feature and their position will be affected by irregularities or errors of form of the periphery. Note : This is illustrated by the enlarged profiles. The center point of diameter A-A is a point a, and the center point of diameter B-B is point b. These and all other center points must lie within the tolerance zone. The tolerance zone is concentric with this datum center.

CYLI NDRI CAL PART WI TH CYLI NDRI CI TY TOLERANCE

A co m m o n typ e o f p art w h e re th e o u te r d ia m e te r is re qu ire d to be co n ce n tric w ith th e ce n te r bo re , w h ich is de s ign ate d as a d a tu m fe a tu re .

MEASURI NG PRI NCI PLE

To fit a s u itable m an d re l in th e d atu m fe atu re Se t tw o in d icato rs w ith Mas te r Gage s to Ze ro re ad in g Ro tate th e m an d re l w ith co m p o n e n t in V-blo ck Th e d iffe re n ce o f th e re ad in g give s th e co n ce n tricity

EFFECTS OF ERRORS OF CONCENTRI CI TY

Figur e A t heor et ical Per f ect f or m

Bot h indicat or s r ead Zer o-Zer o as t he par t is r evolved Figur e B r epr esent s eccent r ic par t The upper indicat or r ead 0.05 and lower indicat or r ead +0.05 when r evolved by 90deg bot h indicat or s r et ur n t o zer o

EFFECTS OF ERRORS OF CONCENTRI CI TY

Figure C represent s a oval part Bot h indicat ors read 0. 12 when revolve by 90deg. Bot h indicat ors ret urn t o zero Figure D represent s a t hree lobed part (cent er is high by 0. 05) when revolve by 60deg. The upper indicat or reads 0. 1 and lower one reads zero (cent er is 0. 05 low) The upper indicat or reads zero W hile t he lower reads 0. 1

TWO- FEATURE DATUM

MEASURI NG W I TH VEE- BLOCK

MEASURI NG WI TH VEE- BLOCK

CONCENTRI CI TY REFERENCED TO DATUM SYSTEM

Toler ance zone is per pendicular t o dat um A and also concent r ic wit h t he axis of dat um B in t he plane of dat um A The par t is mount ed on dat um A and cent er ed on dat um B, and t he j ob is r evolved while t he cont r olled f eat ur e is cont act ed by t wo opposing indicat or s. I t should be not ed t hat t his t oler ance aut omat ically cont r ols t he st r aight ness of t he cent er line of t he 25mm por t ion and it s per pendicular it y wit h dat um A wit hin t he same t oler ance.

Runout

Correlat ive Tolerances RunoutRunout is t he deviat ion in posit ion of a surf ace of revolut ion as a part is revolved about a dat um axis.

A r un out t oler ance r epr esent s t he maximum per missible var iat ion of posit ion of a sur f ace, measur ed at a f ixed point , when t he par t is r evolved wit hout axial movement t hr ough 360 about t he dat um axis. The t oler ance zone is t he ar ea or space, of unif or m t hickness, bet ween t wo shapes coaxial wit h t he dat um axis and par allel t o t he t r ue pr of ile of t he cont r olled sur f ace. The r unout var iat ion is measur ed nor mal t o t he sur f ace being cont r olled by cont act ing t he sur f ace wit h an indicat or gage while t he par t is r evolved on it dat um axis The r unout er r or is t he f ull movement of t he indicat or

Circular Runout and Tot al Run Out

Circular Runout

Tot al Runout

Cir cular Runout Concer ns Runout of each Cir cular element or Cr oss Sect ion Tot al Runout pr ovides composit e cont r ol of all sur f ace element s

CI RCULAR RUNOUT OF CYLI NDRI CAL FEATURES

Cir cular Runout is measur ed at Sever al posit ions along t he sur f ace At each posit ion t he indicat or movement dur ing one r evolut ion of par t must not exceed t he specif ied t oler ance(0.1mm) For Cylindr ical f eat ur e r unout er r or is caused by eccent r icit y and er r or s of r oundness Cir cular Runout is not af f ect ed by a t aper (conicit y) or er r or s of st r aight ness of t he st r aight line element s such as bar r el shaping

ANGULAR RUNOUT AND TOLERANCE ZONE

Cir cular Runout may be applied t o sur f ace of r evolut ion which ar e any desir ed angle in t he r elat ion t o t he dat um axis Measur ement s ar e made at each cr oss-sect ion of t he complet e pr of ile. I ndicat or t o be nor mal t o t he sur f ace of measur ement

RUNOUT PERPENDI CULAR TO AXI S

Er r or will be shown if t he sur f ace is not f lat but not per pendicular t o axis (wobbling) No Er r or be indicat ed if t he sur f ace convex or concave but ot her wise per f ect

RUNOUT OF CURVED SURFACE

RUNOUT OF CURVED SURFACE

Measur ement s ar e always made nor mal t o t he cur ved sur f ace

RUNOUT OF CURVED SURFACE

RUNOUT IN SPECIFIED DIRECTION

All measur ement s ar e made in t he same dir ect ion of axis if specif ied in t he dr awing

45 O

t o t he

TOTAL RUNOUT

Tot al r un out concer ns t he r unout of a complet e sur f ace, not mer ely t he r unout of each cir cular element . For measur ement pur poses t he checking indicat or must t r aver se t he f ull lengt h or ext ent of t he sur f ace while t he par t is r evolved about it s dat um axis Measur ement s ar e made over t he whole sur f ace wit hout r eset t ing t he indicat or . Tot al r unout is t he dif f er ence bet ween t he lowest indicat or r eading in any posit ion, and t he highest r eading in t hat or in any ot her posit ion on t he same sur f ace.

Tot al runout

TOLERANCE ZONE FOR TOTAL RUNOUT

TOTAL RUNOUT

MEASURI NG TOTAL RUNOUT ON CONI CAL PART

For conical sur f aces t he dat um axis can be t ilt ed t o t he t aper angle so t hat t he measur ed sur f ace becomes par allel t o a sur f ace plat e