Geometric Dimensioning and Tolerancing

(Known as GDT)

What is GDT

Helps ensure interchangeability of parts.

Use is dictated by function and relationship of the part feature.

It does not take the place of conventional tolerancing.

ASME GD &T Standards

• ASME Y14.5 Dimensioning and Tolerancing • ASME Y14.5.1 Mathematical Definition of Dimensioning and Tolerancing Principles • ASME Y14.5.2 Certification of Geometric Dimensioning and Tolerancing Professionals • ASME Y14.31 Undimensioned Drawings • ASME Y14.43 Dimensioning and Tolerancing Principles for Gages and Fixtures • ASME Y14.1 Decimal Inch Drawing Sheet Size and Format • ASME Y14.1M Metric Drawing Sheet Size and Format

GD&T Symbols

• Five basic types: - Dimensioning symbols - Datum feature and datum target symbols - Geometric characteristic symbols - Material condition symbols - Feature control frame

Drawn according to specific ASME Y14.5 format

- Size based on drawing lettering height (typically .12 in. or 3 mm)

- Draw using thin lines (.01 in. or 0.3 mm thick)

Datum’s

• Reference features of an object - Planes - Points - Lines - Axes

• The true geometric counterpart of a datum feature • Establish location and size dimensions

Datum Feature Simulators

• The opposite shape of the datum feature • Two types:

- Theoretical datum feature simulator - Physical datum feature simulator

• Manufacturing examples: - Machine tables - Surface plates - Gauge surfaces - Surface tables - Rotation devices

Datum Feature Symbol

• Drawn using thin lines • Symbol size relates to the drawing lettering height • Identify each datum feature with a different letter except I, O, and Q • Not applied to centerlines, center planes, or axes

Datum Feature

Datum Feature Symbol Placement

Datum Surface

• Can be controlled by a geometric tolerance • Measurements taken from a datum plane do not take into account any variations of the

datum surface from the datum plane

Geometric Control of Datum Surface

Datum Reference Frame (DRF)

• Used for layout purposes • Select three datum features that are perpendicular to each other • Assign precedence and datum reference order:

- Primary datum - Secondary datum

- Tertiary datum

• All parts have six degrees of freedom - Three degrees of translation - Three degrees of rotation

• Movement is translational or rotational

Multiple Datum Reference Frames; Example

• Datum reference X, Y, and Z • Datum reference L and M

Datum Features Specified Individually

• Place a note next to datum feature symbols indicating how many datum features to consider separately.

• Place the note “2X INDIVIDUALLY” next to datum feature symbols of two separate datum features identified by same letter.

Using Datum Target Symbols

• Identify datum targets • Useful on parts with surface or contour irregularities • Connect to datum target point, line, or area with a leader • Drawn using thin lines • Movable datum target

Establishing Datum Target Points

• Establish primary datum plane by locating at least three points on primary datum Surface.

• Establish secondary datum plane by locating at least two points on related secondary datum surface.

• Establish tertiary datum plane by locating at least one point on related tertiary datum Surface.

• Dimension using baseline or chain dimensioning. • Location dimensions originate from datums .

Locating Datum Target Points

Use basic dimensions or tolerance dimensions.

Locating Datum Target Areas

Locating Datum Target Lines

Establishing a Partial Datum Surface

Establishing Coplanar Datum Surfaces

• Surfaces treated as a single, interrupted surface • Continuous feature symbol, or • Note below the related feature control frame

\

Establishing Coplanar Datum Surfaces (con)

Establishing a Datum Axis

• A cylindrical object can be a datum feature.

• Represents two theoretical planes intersecting at 90.

• Represented in drawings with centerlines.

• Pitch cylinder for screw threads establishes datum axis unless otherwise specified - When not using pitch cylinder for screw threads, place note such as "MAJOR DIA" or

"MINOR DIA" next to datum feature symbol

• Simulated datum axis established by inspection equipment

Establishing a Datum Axis Illustrated

Datum Feature Symbol Placement for a Datum Axis

Coaxial Datum Features

• A single datum axis is established by two datum features that are coaxial

Datum Axis established with Datum Target Symbols

• Primary datum axis established by two sets of three equally spaced targets. • Identify datum target points in correlation to adjacent cylindrical datum feature when

two cylindrical features of different diameters establish a datum axis. • Cylindrical datum target areas and circular datum target lines can be used to establish

datum axis - Target area represented by two phantom lines with section lines between - Datum target line represented by phantom line all around part

• Establish secondary datum axis by placing three equally spaced targets on cylindrical Surface.

Movable Datum Target Symbols with Datum Target Points

• When datum targets establish a center point, axis, or center plane on a RMB basis, datum feature simulator movement is normal to true profile.

Establishing a Datum Center Plane

• Axis and center plane datum feature symbols align with/replace dimension line arrowhead or appear on feature, leader shoulder, dimension line, or feature control frame.

Material Condition and Boundary Symbols

• Appear with geometric tolerance or datum reference in feature control frame • Modify geometric tolerance in relationship to actual produced size of feature

• Regardless of feature size (RFS) and regardless of material boundary (RMB) are assumed.

Limits of Size Application

Perfect Form Boundary

• Parts produced at MMC must be at perfect form. • For a part at LMC, form tolerance can vary within geometric tolerance zone to extent of

MMC boundary. • Independency symbol specifies that perfect form at MMC is not required.

Regardless of Feature Size (RFS) and Material Boundary (RMB)

• Assumed when no material condition or boundary condition symbol is specified - RFS applies with respect to individual geometric tolerance - RMB applies to datum reference

• Circularity, cylindricity, profile, circular runout, total runout, concentricity, and

symmetry are applied only on an RFS basis

• Tolerance specified using RFS is held at any produced size within specified dimensional

tolerance

Surface Geometric Control, Regardless of Feature Size (RFS)

• RFS is implied if MMC or LMC is not specified. • Surface control is not associated with a size dimension. • Each longitudinal element of the surface must lie between two parallel lines of the

geometric tolerance zone. • Perfect form boundary example: • Diameter symbol in front of the geometric tolerance in the feature control frame

specifies diameter tolerance zone.

Applying Maximum Material Condition (MMC)

• Indicated maximum amount of material for feature - Maximum shaft diameter - Minimum hole diameter

• Specified geometric tolerance is held only at MMC produced size • External feature formula:

- MMC – Produced Size + Given Geometric Tolerance = Applied Geometric Tolerance

• Internal feature formula: - (Produced Size – MMC) + Given Geometric Tolerance = Applied Geometric Tolerance

Axis Control, Maximum Material Condition (MMC)

Applying Least Material Condition (LMC)

• Indicates least amount of material for feature. - Minimum shaft diameter - Maximum hole diameter

• Given geometric tolerance is held at LMC produced size. • No requirement for feature to maintain perfect form when produced at the LMC size

limit. • External feature formula:

- Produced Size – LMC + Given Geometric Tolerance = Applied Geometric Tolerance • Internal feature formula:

- LMC – Produced Size + Given Geometric Tolerance = Applied Geometric Tolerance

Application of RMB on Primary Datum Feature

• RMB is implied for datum features influenced by size and form variations unless otherwise specified.

• When a datum feature has a size dimension and form tolerance, size of simulated datum is MMB size limit.

- Boundary can exceed MMB when axis straightness is specified. • For a datum feature of size, establish datum by contact between datum feature surface

and surface of processing equipment. • Simulated datum is axis of datum feature simulator.

- External feature: Smallest circumscribed perfect cylinder that contacts datum feature surface

- Internal feature: Largest inscribed perfect cylinder that contacts datum feature surface

Application of RMB on a Primary Datum Center Plane

• Simulated datum is center plane of datum feature simulator. - External feature:

Two parallel planes that contact datum feature surface at minimum separation.

- Internal feature: Two parallel planes at maximum separation.

Application of RMB on a Secondary and Tertiary Datum Feature

• Secondary - Contacting datum Use same guidelines for primary datum axis or center plane

except: feature simulator is 90, or another design angle, to primary

datum, which is usually an adjacent plane • Tertiary

- Use same guidelines for secondary datum axis or center plane except: Contacting datum feature simulator is 90, or another

design angle, to primary and secondary datums

The Effect of Datum Precedence and Material Condition

• Closely examine effect of material condition on datum when assigning precedence. - Changes in precedence alter part fit and function

• Consider options available when specifying datum requirements

Geometric Characteristic Symbols • Provide specific controls related to the:

- Form of an object - Orientation of features - Outlines of features - Relationship of features to an axis - Location of features

The Feature Control Frame Symbol Feature Control Frame with Datum Reference

Form Tolerances • Applied to single features or elements of single features. • Not related to datum’s. • Used to control:

- Straightness - Flatness - Circularity - Cylindricity

Straightness Tolerance

• Applied to control surface or axis straightness.

Surface Straightness Tolerance • Feature cannot exceed MMC envelope and must maintain perfect form if actual size is

produced at MMC. • Otherwise, RFS applies and geometric tolerance remains the same at any produced size.

Axis Straightness • Place feature control frame below diameter dimension. • Place diameter symbol in front of geometric tolerance. • Allows a violation of perfect form at MMC. • RFS assumed.

Axis Straightness at MMC • Place MMC symbol after the geometric tolerance. • Specified geometric tolerance held at MMC and can increase as actual size departs from

MMC. • Acceptance boundary can be used as a functional gage to verify the part. • Local size is also verified.

Unit Straightness • Specifies straightness per unit. • Prevents an abrupt surface variation within a relatively short length of the feature. • Tolerance over total length is greater than unit tolerance. • Per unit specification given per inch or per 25 mm of length • Derived axis or centerline of the actual feature lies within a cylindrical tolerance zone

for: - Total length - Any 25 mm length, RFS

Straightness of Non-cylindrical Features • Controls median plane of the part within specified straightness tolerance. • Use a leader or extension line to attach feature control frame to surface in a view where

the surface appears as a line. - Do not place diameter symbol in front of geometric tolerance.

• Apply straightness of a rectangular part at RFS or MMC • Generally appropriate for thin features Straightness of a Flat Surface • Straightness geometric tolerance controls single line elements on surface in one or two

directions. • Determine tolerance zone direction by feature control frame placement.

Straightness of a Limited Length • Apply straightness to a portion of a long part using a chain line next to view at desired

straightness length. - Dimension length of chain line. - Connect feature control frame to chain line with a leader.

• Apply to a cylindrical or flat part.

Flatness Tolerance • Establishes flatness tolerance zone.

- Always considered RFS when applied to a surface.

Flatness Applied to a Size Dimension • In a typical application, derived median plane of feature lies within two parallel planes

spaced equal to specified flatness geometric tolerance. • Apply geometric tolerance at RFS or MMC.

Specific Area Flatness

• Use when a large cast surface must be flat in relatively small area. - Machine only required area

• Outline specific area with phantom lines - Add section lines within area

• Locate specific area from datum’s with basic or ± dimensions. • Connect feature control frame to area with leader line.

Unit Flatness

• Use alone or in combination with a total tolerance. • Most applications use unit flatness with a total tolerance over entire surface so the unit

callout does not become unmanageable. • Unit tolerance must be smaller than total tolerance. • Specify unit flatness using a square, rectangular, or circular unit area.

Circularity Tolerance

• Establish from periphery, shaft circumference, or inside diameter of a hole. • Does not reference a datum and is always RFS. • Must be less than size tolerance. • Feature control frame connects to the view where the feature appears as a circle or in

the longitudinal view.

Circularity Tolerance (con)

Circularity Tolerance for a Sphere • Established by two concentric circles created by a plane passing through the sphere’s

center. • All points on surface must lie within circularity tolerance zone.

Free State Variation Applied to Circularity

• Typical in non-rigid parts. • Circularity specification of a nonrigid part can be based on average diameter.

- Place free state symbol in feature control frame after geometric tolerance and material condition symbol

- Place “AVG” after size dimension

Cylindricity Tolerance

• Form tolerance not referenced to a datum. • Geometric tolerance must be less than size tolerance. • Always RFS. • Composite control of circularity, straightness, and taper.

Orientation Geometric Tolerances

• Use to establish “total” control of feature relationships: - Parallelism - Perpendicularity - Angularity - Profile (in some cases)

Orientation Tolerances

• Controlled feature relates to one or more datum features. • EACH ELEMENT or EACH RADIAL ELEMENT note allows for control of individual surface

elements. • When tolerance is applied to a plane surface, flatness is controlled to the extent of the

orientation tolerance. • RFS is implied.

Surface Parallelism

• Requires parallelism geometric tolerance. • Actual surface must be within parallelism tolerance zone established by two planes

parallel to the datum. • Parallelism tolerance zone must be within specified size limits.

Tangent Plane • Additional requirement applied to a surface control. • Symbol placed after geometric tolerance in feature control frame. • Actual surface can be outside parallelism geometric tolerance zone. • Tangent plane must be within parallelism geometric tolerance zone.

Axis Parallelism • Applied for a feature axis by establishing two parallel planes parallel to a datum plane

between which the axis must lie. • Parallelism tolerance zone must be within specified location tolerance. • Feature control frame appears with diameter dimension. • Diameter dimension associates the related geometric tolerance with feature axis. • RFS is assumed.

• Can be applied to the axes of two or more features. • Axis of feature must lie within cylindrical tolerance zone parallel to datum axis

- Diameter tolerance zone.

• RFS assumed unless applying MMC or LMC Parallelism of Line and Radial Elements

• Place note EACH ELEMENT below feature control frame to control only individual line Elements.

- Only controls elements in a plane parallel to view in which the tolerance is given.

• Place note EACH RADIAL ELEMENT under feature control frame to control parallelism for individual line elements on a radial surface.

Perpendicularity of a Surface • Requires perpendicularity tolerance. • Always RFS. • Requires datum reference. • Surface can be held perpendicular to one datum plane or two datum planes

- Surface held perpendicular to two datum planes is between two parallel planes perpendicular to two datum planes.

- Feature control frame references both datum’s.

Perpendicularity of an Axis • Established by two parallel planes perpendicular to a datum plane or axis within which

the axis feature must lie. • Place feature control frame below diameter dimension. • Only applies in view where dimension is shown. • RFS implied unless applying MMC or LMC. • Apply cylindrical perpendicularity tolerance zone by placing diameter symbol in front of

geometric tolerance in feature control frame.

Perpendicularity of a Center Plane

• Specifies symmetrical feature as perpendicular to datum plane. - Feature center plane held within two parallel planes that are perpendicular to a datum

plane. - Center plane must be within the specified location tolerance.

Perpendicularity of Line Elements and Radial Elements • When controlling individual line elements of a surface, use note:

- EACH ELEMENT below feature control frame

• When controlling individual line elements of a radial surface, use note: - EACH RADIAL ELEMENT under feature control frame

Combining Parallelism and Perpendicularity • Allows versatility by providing uniform parallelism and perpendicularity to related

datums. • Tolerance zones are different or same. • Stack feature control frames to provide feature control frame compartment for each

geometric tolerance. Angularity Tolerance

• Angle must be basic from the datum plane. • RFS implied unless otherwise specified.

Angularity of an Axis • Can be used to control feature axis between two parallel planes.

- Planes are spaced equally on each side of specified basic angle from datum plane or axis.

- Axis of feature must lie within this zone. - Only applies to view where specified. - Feature control frame appears next to feature diameter dimension to specify axis

control.

• Can be used to control feature axis within a cylindrical angularity tolerance zone. - Place diameter symbol in front of geometric tolerance in feature control frame. - Specifies cylindrical tolerance zone.

Angularity of a Center Plane and Single Element Control • Angularity tolerance formed by two parallel planes at specified basic angle to datum

plane. • Center plane of feature must lie within this zone. • Used for single line element or single radial element control.

- Place note EACH ELEMENT or EACH RADIAL ELEMENT below feature control frame.

Applying Zero Orientation Tolerance at MMC • Can be used for parallelism, perpendicularity, or angularity. • Feature has perfect orientation at MMC.

Location Tolerancing • Uses location tolerances.

- Positional tolerance - Concentricity tolerance - Symmetry tolerance

Positional Tolerancing • Used to establish location of features from true position. • Provides benefits over conventional methods. • Include diameter symbol when applied to a cylindrical tolerance zone.

- Add compartments for datum reference - MMC or LMC symbol appears after tolerance - Assume RFS or RMB unless MMB or LMB symbol follows specified datum reference

• Establishes cylindrical tolerance zone when applied to a cylindrical feature.

• When applied to a noncylindrical feature, tolerance value represents distance between

two parallel straight lines or planes or distance between two uniform boundaries.

Comparing Conventional Tolerancing and Positional Tolerancing

• Conventional tolerancing establishes surface tolerance zone. - Uses ± or limit location dimensions. - Actual hole center is anywhere within the square area. - Diagonal of zone is greatest distance that allows variation in center location. - Diagonal becomes diameter tolerance zone cylindrical through thickness of part.

• Positional tolerancing provides increase of 54% in permissible area for the hole location

• Use guidelines when converting a drawing from conventional tolerancing

- Add datums

- Change location dimensions from ± to basic

- Add feature control frame to diameter dimension

Positional Tolerance Zone

• Hole axis at true position • Positional tolerance at MMC

Positional Tolerance Zone (con)

• Hole axis at extreme positional variation. • Positional tolerance at MMC. • Positional tolerance at MMC.

• Hole axis at extreme attitude variation. • Positional tolerance at MMC.

• Hole axis at true position • Positional tolerance at LMC

Positional Tolerance at MMC • Tolerance increases equal to amount of change from MMC. • Maximum positional tolerance occurs at LMC. • Internal feature formula:

- Actual Size – MMC + Specified Positional Tolerance = Applied Positional Tolerance. • External feature formula:

- MMC – Actual Size + Specified Positional Tolerance = Applied Positional Tolerance.

Introduction to Virtual Condition

• Internal feature: - MMC OF FEATURE – RELATED GEOMETRIC TOLERANCE = VIRTUAL CONDITION.

• External feature: - MMC OF FEATURE + RELATED GEOMETRIC TOLERANCE = VIRTUAL CONDITION.

Positional Tolerance Based on the Surface of a Hole

• All elements of hole surface must be outside a theoretical boundary located at true position and produced within specified size limits.

Zero Positional Tolerancing at MMC

• Allows positional tolerance zone to exceed amount specified when feature is produced at any actual size other than MMC.

• Specifies importance of certainty that tolerance is totally dependent on actual size of feature.

• True position required at MMC. • Positional tolerance increases equal to amount of departure as feature size departs

from MMC. • Total allowable variation in positional tolerance is at LMC.

Positional Tolerance at RFS • Assume RFS when no material condition symbol appears after positional tolerance. • Apply RFS to positional tolerance when it is desirable to maintain given positional

tolerance at any produced size. - RFS requires closer control of features.

• Used to control relationship of feature surface and true position of largest hole size. • Sometimes controls minimum edge distance or minimum wall thickness. • Positional tolerance held at LMC. • Positional tolerance increases equal to amount of change from LMC as produced size

departs from LMC toward MMC.

• Maximum positional tolerance is at MMC.

• Requires perfect form at LMC.

Calculating Positional Tolerance at LMC

• Internal feature: - LMC – Actual Size + Specified Positional Tolerance = Applied Positional Tolerance

• External feature: - Actual Size – LMC + Specified Positional Tolerance = Applied Positional Tolerance

Locating Multiple Features

• Use rectangular coordinate dimensioning in positional tolerancing applications

• Use polar coordinate dimensioning to establish angular dimensions in positional tolerancing applications.

Locating a Single Composite Pattern

• Location dimensions are basic from datum reference frame.

• All holes checked together.

Locating Features in Patterns with Separate Requirements

• Used when a multiple datum reference frame exists and features are positioned to different datum’s individually.

• Place note next to datum feature symbols and related feature control frame identifying how many datum features and position tolerance specifications to consider individually.

- Example: 2X INDIVIDUALLY

Composite Positional Tolerance

• Double the feature control frame in height and divide into two parts. - Use one positional geometric characteristic symbol in one double height feature

control frame compartment. - Specify pattern-locating control in upper part of feature control frame. - Specify feature-relating control in lower entry.

Composite Positional Tolerance (con)

Two Single-Segment Feature Control Frames

• Display two position symbols, each in a separate compartment. - Specify pattern-locating control in top half of feature control frame. - Single datum reference in lower half of feature control frame provides orientation. - Double datum reference provides orientation and alignment for feature-relating

control.

• Offers tighter relationship of holes within pattern.

• Pattern-locating zones and feature-relating zones must remain same distance from

secondary datum.

Two Single-Segment Feature Control Frames (con)

Composite Positional Tolerancing Applied To Circular Patterns

• Pattern-locating zones located using a basic diameter and basic angle between features.

- Oriented to specified datum reference frame

• Feature-relating zones located partially or totally within boundaries of pattern-locating Zones.

- Held perpendicular to primary datum - Controlled as group by basic dimensions -

• Feature axes must fall within both zones.

Composite Positional Tolerancing Applied To Circular Patterns (con)

Two Single-Segment Tolerance Applied to Circular Patterns

• Top half of feature control frame controls location of features as a group to the datum’s.

• Add slot and tertiary datum to pattern-locating control to provide orientation of the pattern of holes.

• Lower portion of feature control frame controls pattern of features related to each other.

Two Single-Segment Tolerance Applied to Circular Patterns (con)

Material Condition Requirements In Composite Positional Tolerancing

• Composite and two single-segment feature control frames must have same material condition.

• Datum’s must be in same order of precedence with same boundary condition.

Position Tolerancing of Coaxial Features

• Used for features with a common axis. - Holes and counterbores.

• When tolerance is same for both features, positional tolerance zone diameter is same for both features relative to specified datum’s.

• Feature control frame appears below note to specify hole and counterbore. • When different tolerances are applied to coaxial features related to the same datum

features, separate feature control frames are used.

- One feature control frame appears under note to specify hole size. - Another feature control frame appears under note to specify counterbore.

• When tolerances control individual counterbore-to-hole relationships relative to

different datum features, an additional specification is required.

- A note appears under the datum feature symbol for the hole and under the feature

control frame for the counterbore to indicate number of places each applies on an

individual basis

Coaxial Positional Tolerance of Features in Alignment

• Used for holes lying apart and in alignment. • Locate positional tolerance zone of holes by basic dimensions from referenced datum’s. • Each hole can be produced at any location within positional tolerance zone.

Position Tolerancing of Non-parallel Holes

Locating Slotted Features

• Locate to centers with basic dimensions from datum’s. • When a greater positional tolerance is placed on the length than on the width, add a

feature control frame to the length and width dimensions. • Use a bidirectional positional tolerance for a greater location tolerance in one direction

than the other direction.

- Positional tolerance results in a rectangular tolerance zone.

- Omit diameter symbol from the feature control frame.

- Positional tolerance zone is non-cylindrical.

• When the positional tolerance is controlled in relation to the feature surfaces, each

feature is controlled by a theoretical boundary.

- Size of each slot is within size limits and no portion of surface can enter theoretical

boundary.

- Precede feature control frame with number of slots, such as 2X.

• Boundary formula:

- MMC Length – Positional Tolerance = Boundary Length

- MMC Width – Positional Tolerance = Boundary Width

Position Tolerancing of Spherical Features

• Spherical diameter symbol precedes feature size dimension.

• Feature control frame appears below size dimension and positional tolerance zone is spherical.

Applying Positional Tolerancing to Fasteners

• Fasteners. • Thread symbol represents thread on drawing. • Thread note provides thread specifications. • Unless otherwise specified, geometric tolerances apply to pitch diameter.

Applying Positional Tolerancing to Fasteners (con)

• A: Location tolerance applies to the cylindrical axis of the pitch diameter.

• B: Location tolerance applies to the cylindrical axis of the major diameter,

• C: Location tolerance applies to the cylindrical axis of the minor diameter.

Floating Fasteners

• Floating Fastener Positional Tolerance Formula: - MMC Hole - MMC Fastener (Bolt) = Positional Tolerance for Each Part.

Fixed Fasteners

• Fixed Fastener Positional Tolerance Formula: - MMC Hole – MMC Fastener (Bolt) / 2

= Positional Tolerance for Each Part

Fixed Fastener with Different Positional Tolerances Applied to Each Part

• A greater amount of positional tolerance can apply to unthreaded part. • Example: 70% applied to the unthreaded part and 30% to the threaded part. • Use the formula:

- MMC Hole – MMC Bolt = x x 70% (.70) = Positional Tolerance for Part A x 30% (.30) = Positional Tolerance for Part B

Applying a Projected Tolerance Zone

• Usually specified for fixed fastener applications. • Length is distance fastener extends into the mating part, thickness of the part, or height

of a press-fit stud. • Perpendicularity tolerance provides a tighter control than allowed by a positional

tolerance.

Projected Tolerance Zone Representation First Option

Projected Tolerance Zone Representation Second Option

Virtual Condition

• Determine when designing mating parts. • Violating virtual condition risks the interchangeability of mating parts. • Virtual condition of a feature must be interchangeable with virtual condition of its

mating part.

Calculating Virtual Condition • Internal Feature Formula:

- MMC SIZE OF THE FEATURE – RELATED GEOMETRIC TOLERANCE = VIRTUAL

CONDITION

• External Feature Formula: - MMC SIZE OF THE FEATURE + RELATED GEOMETRIC TOLERANCE = VIRTUAL

CONDITION

Zero Positional Tolerance at MMC with the Clearance Hole at Virtual Condition

Concentricity Geometric Tolerance

• Establishes concentricity. • Specifies a cylindrical tolerance zone. • Axis of tolerance zone coincides with datum axis. • Specifies that median points originating from feature surface must be within cylindrical

concentricity tolerance zone.

• Applied only on an RFS basis.

• Related datum reference

applied only on an RMB basis.

Concentricity Geometric Tolerance

• Form irregularities of an actual feature can make it difficult to establish location of median points.

- Finding median points requires analysis of surface variations. - Use runout or positional tolerancing unless it is absolutely necessary to control median

points.

Symmetry Geometric Tolerance

• Applied only on an RFS basis. • Related datum reference applied only on an RMB basis. • Presents difficulty in inspecting median points. • Consider positional tolerance locating symmetrical features if symmetry is not required.

Positional Tolerancing Locating Symmetrical Features

• Establishes a center plane-to-center plane control. • Use to locate one or more features symmetrically with respect to center plane of datum

feature. • Omit diameter symbol in feature control frame. • Positional tolerance zone is distance between two parallel planes equally divided on

each side of true position. • Material condition must accompany positional tolerance.

- RFS assumed otherwise.

Zero Positional Tolerance at MMC for Symmetrical Objects

• Use to control symmetry relationship of features within their limits of size. • Datum feature usually specified on MMB basis. • Perfect symmetry occurs and a boundary of perfect form is established when positional

controlled feature is at MMC and datum feature is at MMB. • Out-of-perfect symmetry only happens as produced size leaves MMC.

Applying Profile Tolerances

• Profile can be used to control form or combinations of size, form, and orientation. • Based on true profile. • Must be contained within size tolerance when used as a refinement of size. • Always RFS. • Equally disposed bilateral unless otherwise specified. • Profile geometric tolerance zone is generally oriented to one or more datum’s.

Profile of a Line Tolerance

• Used when it is unnecessary to control profile of the entire feature. • Used when parts have changing cross sections throughout length. • Assumed to be equally disposed bilateral when leader from feature control frame

extends to related surface without any additional clarification.

Profile of a Line between Two Points

• Place the between symbol under feature control frame.

• Use any combination of letters. • Establish true profile with a basic

or tolerance dimension. • Equally disposed bilateral unless

otherwise specified. • Feature confined within profile

tolerance zone.

Profile of a Line All Around

Unilateral Profile of a Line

• Place the unequally disposed symbol after geometric tolerance in feature control frame. • Repeat tolerance value after unequally disposed symbol when the tolerance has

material added to feature or part.

Unilateral Profile of a Line (con)

• Place tolerance value before the unequally disposed symbol when the tolerance has material taken from the feature or part.

• Place a 0 after the unequally disposed symbol. • Specifies entire profile tolerance is inside of true profile.

Alternate Unilateral Profile Tolerance Option

• Draw a short phantom line parallel to the true profile on the side of the intended unilateral tolerance.

• Place a dimension line with an arrowhead on the far side and connect a leader line to feature control frame with a leader line on the other side.

Unequally Disposed Profile of a Line

• Place total profile tolerance value before the unequally disposed symbol in feature control frame.

• Place value of tolerance that adds material to the feature or part after the unequally disposed symbol.

Unequally Disposed Profile of a Line

Alternate Unequally Disposed Profile Tolerance Option

• Show either inside or outside of true profile as a basic dimension. • Place a dimension line with arrowheads on each side of the phantom lines and connect

feature control frame with a leader. • Actual profile of part must be between the basic zone created around the true profile.

Profile of a Surface Tolerance

• Use to control entire surface as a single feature. • Extends along total length and width or circumference of object or feature(s)

- Establishes a blanket tolerance. • Equally disposed bilateral unless otherwise specified. • Normally requires reference to datum’s for proper orientation of profile.

Profile of a Surface Between Two Points

Profile of a Surface All Around or All Over

• Establishes a blanket tolerance. • Surfaces all around or all over object outline must lie between two parallel boundaries

equal in width to given geometric tolerance. • Tolerance zone should be perpendicular to datum plane.

Profile of a Sharp Corner

• Tolerance zone extends to intersection of the boundary lines. • A rounded corner can occur. • Control using a maximum radius note.

Unilateral or Unequally Disposed Profile of a Surface

Coplanar Profile Tolerance

• Used to control profile of coplanar surfaces as a single surface.

• Place a phantom line between surfaces in the view where required surfaces appear as lines.

• Connect a leader from feature control frame to phantom line and add a note below feature control frame identifying the number of surfaces.

Profile of Plane Surfaces

• Used to control form and orientation of planar surfaces. • Can be used to control the angle of an inclined surface in relationship to a datum.

- Surface must lie between two parallel planes equally split on each side of a true plane that has a basic angular orientation to a datum.

Profiles of Conical Features • Controls form or form and orientation. • Controls feature independently as a refinement of size or orients feature to a datum

axis. • Profile tolerance must be within the size tolerance. • Actual surface must lie between two coaxial boundaries equal in width to the specified

geometric tolerance, having a basic included angle, and within the size limits.

Composite Profile Tolerance

• Double the feature control frame in height. • Place geometric characteristic symbol in first compartment . • Specify locating tolerance zone in top half of feature control frame.

- Give datum reference in order of precedence in feature control frame - Locate feature to be controlled from datum’s with basic dimensions

• Specify profile form and orientation tolerance zone in bottom half of feature control

frame.

- Datum referencing establishes limits of size, form, and orientation of profile related to

locating tolerance zone

• Actual feature surface must be within both tolerance zones.

Profile of a Feature to be Restrained

• Identify datum features. • Provide a note specifying process used and force required to restrain the part.

Runout Geometric Tolerance

• Used to control surfaces constructed around or perpendicular to a datum axis. - Control of circular elements of a surface. - Control of cumulative variations of circularity, straightness, coaxiality, angularity,

taper, and profile of a surface. - Control of variations in perpendicularity and flatness.

• Always specified RFS. • Datum references always specified RMB. • Connect feature control frame to surface by a leader line. • Use multiple leaders to direct a feature control frame to two or more surfaces having a

common runout tolerance.

Circular Runout

• Controls circularity and coaxiality when applied to surfaces constructed around or perpendicular to a datum axis.

• Can be used to control wobbling motion. • Controlling datum verified before checking other surfaces. • Reference datum always RMB. • Measured by full indicator movement (FIM) of a dial indicator placed at several circular

measuring positions as part is rotated 360.

• FIM is a total tolerance.

• Each circular element must lie within the FIM.

• Establish datum axis for runout inspection using a clamping device

- Collet typical.

Total Runout

• Controls combined variations of circularity, straightness, coaxiality, angularity, taper, and profile when applied to surfaces constructed around and at right angles to a datum axis.

• Can control combined variations of perpendicularity. • Can control concavity or convexity when applied to surfaces perpendicular to a datum

axis. • Reference datums always RMB.

• Tolerance zone encompasses entire surface as part is rotated 360. - Entire surface must lie within specified tolerance zone.

- Dial indicator is placed at every location along surface as part is rotated 360.

Applying Runout to a Portion of a Surface and Two Datum References

• Place a chain line located with basic dimensions in linear view. - Connect feature control frame to chain line by a leader.

• Place datum identifying letters in feature control frame. • Separate letters by a dash.

Applying Runout to a Datum Surface and a Datum Axis • Place datums separately in feature control frame in order of precedence. • Profile must be within specified geometric tolerance when part is mounted on the

datum surface and rotated 360 about the datum axis. • Datum reference always specified RMB.

Applying Runout Control to a Datum

• Specify datum feature symbol to apply runout. • Center datum feature symbol below feature control frame or connect datum feature

symbol to the leader shoulder.

Combining Runout with Other Geometric Tolerances

• Used in runout tolerancing applications. - Profile and circular runout. - Runout and cylindricity .

Specify Independency

• Form control is independent of size tolerance and should be added to the feature. • Size is verified by a two-point check using a micrometer or caliper. • Form is checked using the runout tolerance.