GD&T POSITION TOL

GD&T Location Table of ContentsReturn to the Previous Slide Slide 1 QuitMaster Table of ContentsGlossary

ConcentricityConcentricity

SymmetrySymmetry

Position Position

These are the three geometric tolerance These are the three geometric tolerance controls and their associated symbols, that are controls and their associated symbols, that are available within the family of location available within the family of location tolerances.tolerances.

LOCATION TOLERANCESLOCATION TOLERANCES


DEFINITIONDEFINITION•Concentricity is normally applied to Concentricity is normally applied to (Two or more)(Two or more) features that are required to features that are required to revolve around a datum axis. A time- and resource-intensive verification processrevolve around a datum axis. A time- and resource-intensive verification process—usually involving a complex mathematical analysis—is required.—usually involving a complex mathematical analysis—is required.

•ConcentricityConcentricity is a condition where the median points of all diametrically is a condition where the median points of all diametrically opposed elements of a feature of revolution around an axis coincide with the axis opposed elements of a feature of revolution around an axis coincide with the axis or center point of a datum feature. or center point of a datum feature.

•Concentricity is always applied to features of size, always applies regardless of Concentricity is always applied to features of size, always applies regardless of feature size, and always requires a datum reference. Afeature size, and always requires a datum reference. A concentricity tolerance concentricity tolerance and its datum reference and its datum reference can only apply regardless of feature size and therefore, can only apply regardless of feature size and therefore, cannot be modified to MMC or LMC, cannot be modified to MMC or LMC,




Concentricity is most often thought of as a coaxiality control, and because it must Concentricity is most often thought of as a coaxiality control, and because it must be verified from surface elements, it be verified from surface elements, it alwaysalways applies RFS. Concentricity cannot be applies RFS. Concentricity cannot be applied to a feature; it must applied to a feature; it must alwaysalways be applied to features of size. However, it be applied to features of size. However, it cannot be modified to take advantage of bonus tolerances, and must cannot be modified to take advantage of bonus tolerances, and must alwaysalways reference a datum axis. In addition, fixed (functional) gages cannot be used in the reference a datum axis. In addition, fixed (functional) gages cannot be used in the verification process. Verification must be done with variable gaging—usually verification process. Verification must be done with variable gaging—usually resulting in higher costs.resulting in higher costs.

12 0-0.2

25 0-0.5

0.2 EE


12 0-0.2

25 0-0.5

0.2 EE

ConcentricityConcentricityRegardless of feature size, median points from Regardless of feature size, median points from allall opposing two-point measurements opposing two-point measurements on the head of the pin in this example, must be within a cylindrical tolerance zone, 0.2 on the head of the pin in this example, must be within a cylindrical tolerance zone, 0.2 mm in diameter. A variable gage will be used to secure datum feature E, and mm in diameter. A variable gage will be used to secure datum feature E, and determine the datum axis. Apposing point measurements will then be taken to verify determine the datum axis. Apposing point measurements will then be taken to verify median points for all measurements across the diameter of the head of the pin. The median points for all measurements across the diameter of the head of the pin. The clustering of all derived median points must be within the cylindrical tolerance zone clustering of all derived median points must be within the cylindrical tolerance zone centered around datum axis E.centered around datum axis E.


12 0-0.2

25 0-0.5

0.2 EE

Verifying ConcentricityVerifying Concentricity

At At everyevery measuring measuring location of diametrically location of diametrically opposed elements, a opposed elements, a median point must be median point must be established.established.

12 0-0.2

25

0.2 EE

0-0.5


25 0-0.5

0.2 E

Verifying ConcentricityVerifying Concentricity

12 0-0.2

25

0.2 EE

Regardless of featureRegardless of featuresize, all median pointssize, all median pointsof diametrically opposedof diametrically opposedelements of the featureelements of the featuremust lie within the 0.2 must lie within the 0.2 diameter cylindrical diameter cylindrical tolerance zone, which is tolerance zone, which is also centered around the also centered around the datum axis.datum axis.

0-0.5

12 0-0.2

E

At At everyevery measuring measuring location of diametrically location of diametrically opposed elements, a opposed elements, a median point must be median point must be established.established.


SYMMETRY OF SIZE FEATURESSYMMETRY OF SIZE FEATURES


•SymmetrySymmetry is a condition where the median points of is a condition where the median points of allall opposed or opposed or correspondingly-located elements of two or more feature surfaces are coincident correspondingly-located elements of two or more feature surfaces are coincident with the axis or center plane of a datum feature. with the axis or center plane of a datum feature.

•Symmetry is Symmetry is alwaysalways applied to features of size, applied to features of size, alwaysalways applies regardless of applies regardless of feature size, and feature size, and alwaysalways requires a datum reference. requires a datum reference. A symmetry tolerance and its A symmetry tolerance and its datum reference can only apply regardless of feature size.datum reference can only apply regardless of feature size.

•Symmetry cannot be modified to MMC or LMC. Symmetry cannot be modified to MMC or LMC.

•Symmetry, like concentricity, requires a time- and resource-intensive verification Symmetry, like concentricity, requires a time- and resource-intensive verification process. Median points for process. Median points for allall opposed elements of the controlled feature, must opposed elements of the controlled feature, must be verified.be verified.

DEFINITION:DEFINITION:

SymmetrySymmetry


20.520.0

A

8.88.2

0.4 A

The requirement for this object is that the two sides of the groove be symmetrical about The requirement for this object is that the two sides of the groove be symmetrical about the center plane. The center plane is established by the height feature of size the center plane. The center plane is established by the height feature of size dimension, and the symmetry control is called out in the feature control frame.dimension, and the symmetry control is called out in the feature control frame.

Symmetry of Size Features Symmetry of Size Features


Symmetry of Size Features Symmetry of Size Features

0.4 wide tolerance zone0.4 wide tolerance zone

Center plane of datum feature A, Center plane of datum feature A, ascertained by variable gage.ascertained by variable gage. The The median pointsmedian points of of allall

opposed elements of the opposed elements of the groove (measurements across groove (measurements across the opening and the opening and perpendicular to the center perpendicular to the center plane) must lie between two plane) must lie between two parallel planes 0.4 mm apart, parallel planes 0.4 mm apart, which planes must also be which planes must also be parallel to the center plane. parallel to the center plane.

20.520.0

A

8.88.2

0.4 A


TOLERANCES OF POSITIONTOLERANCES OF POSITION


TOLERANCES OF POSITIONTOLERANCES OF POSITION

Industry uses tolerances of position because they:Industry uses tolerances of position because they:

• control the theoretically exact location of features,control the theoretically exact location of features,

• simulate mating part (worst case) relationships,simulate mating part (worst case) relationships,

• may be modified to MMC and LMC,may be modified to MMC and LMC,

• provide flexibility in verification and simulation,provide flexibility in verification and simulation,

• may be used to control features in coaxial relationships,may be used to control features in coaxial relationships,

• provide symmetrical controls of features relative to a center plane, andprovide symmetrical controls of features relative to a center plane, and

• frequently provide generous margins of cost-savings.frequently provide generous margins of cost-savings.


COORDINATE TOLERANCING COORDINATE TOLERANCING COMPARED TO POSITION COMPARED TO POSITION

TOLERANCINGTOLERANCING


COORDINATE LOCATION COORDINATE LOCATION TOLERANCINGTOLERANCING


Using standard dimensions with plus and minus tolerances, locate the intersecting Using standard dimensions with plus and minus tolerances, locate the intersecting center planes which locate the center line or axis of a feature (in this case, a hole). center planes which locate the center line or axis of a feature (in this case, a hole).

Coordinate tolerancingCoordinate tolerancingof a hole locationof a hole location


Each of the tolerances on the coordinate dimensions is Each of the tolerances on the coordinate dimensions is .005, or .010 inches. .005, or .010 inches. First, add the tolerance limits on the horizontal dimension.First, add the tolerance limits on the horizontal dimension.


24.000 .005

.750 .005


Next add to the drawing the plus and minus value to the vertical dimension.Next add to the drawing the plus and minus value to the vertical dimension.


24.000 .005

.750 .005

.755 (.750 + .005)

.745 (.750 - .005)


The tolerance zone (in this case) will now measure exactly ten thousandths on any The tolerance zone (in this case) will now measure exactly ten thousandths on any verticalvertical or or horizontalhorizontal coordinate. However, when measured along coordinate. However, when measured along anyany other orientation, the distance other orientation, the distance increasesincreases proportionately. proportionately.


24.000 .005

.750 .005

.755 (.750 + .005)

.745 (.750 - .005)

23.995

24.005


The tolerance zone in this case will now measure exactly ten thousandths on any The tolerance zone in this case will now measure exactly ten thousandths on any verticalvertical or or horizontalhorizontal coordinate. However, when measured in any orientation other than vertical or coordinate. However, when measured in any orientation other than vertical or horizontal, the distance horizontal, the distance increasesincreases proportionately, until a maximum is reached at the corners proportionately, until a maximum is reached at the corners of the tolerance zone.of the tolerance zone.


24.000 .005

.750 .005

.755 (.750 + .005)

.745 (.750 - .005)

23.995

24.005

.014


The Coordinate Tolerance DilemmaThe Coordinate Tolerance Dilemma

The assignment of coordinate dimensions with their associated tolerance limits The assignment of coordinate dimensions with their associated tolerance limits (plus/minus or otherwise), creates a set of interesting problems for design (plus/minus or otherwise), creates a set of interesting problems for design personnel. A careful analysis of any design project that has been defined using personnel. A careful analysis of any design project that has been defined using coordinate plus and minus tolerances, reveals the following circumstances that coordinate plus and minus tolerances, reveals the following circumstances that must be dealt with by the designer or engineer:must be dealt with by the designer or engineer:

• Coordinate tolerances produce 3-D rectangular tolerance zones--(width, height, Coordinate tolerances produce 3-D rectangular tolerance zones--(width, height, and depth).and depth).

• The feature axis can be established and exist The feature axis can be established and exist anywhereanywhere within the limits of the within the limits of the tolerance zone.tolerance zone.

• The 3-D diagonal measurement through a rectangular tolerance zone must be The 3-D diagonal measurement through a rectangular tolerance zone must be functionally acceptable to the designer.functionally acceptable to the designer.

• If the diagonal measurement is valid, then generally speaking, shouldn’t the If the diagonal measurement is valid, then generally speaking, shouldn’t the same value be acceptable in all directions?same value be acceptable in all directions?

• Coordinate dimensions for location of features requires additional evaluation to Coordinate dimensions for location of features requires additional evaluation to determine the worst case scenario (diagonal measurements).determine the worst case scenario (diagonal measurements).


POSITION LOCATION TOLERANCING POSITION LOCATION TOLERANCING


.014

.010

.010

Returning to the previous example, let’s examine both the dilemma and a solution. If the Returning to the previous example, let’s examine both the dilemma and a solution. If the designer can live with a tolerance of designer can live with a tolerance of .007 on the .007 on the diagonaldiagonal—in the worst case, then the —in the worst case, then the tolerance of tolerance of .005 for .005 for coordinatecoordinate locating dimensions could be specified, all of which locating dimensions could be specified, all of which compounds the tolerance analysis. Instead of using a rectangular coordinate zone, let’s compounds the tolerance analysis. Instead of using a rectangular coordinate zone, let’s substitute a cylindrical tolerance zone that will allow substitute a cylindrical tolerance zone that will allow .007 in .007 in all directionsall directions from its center. from its center.

Coordinate Location ToleranceCoordinate Location Tolerance


.014

.010

.010

Coordinate Location Tolerance

The tolerance zone for acceptable axis location increases significantly when the tolerance zone is The tolerance zone for acceptable axis location increases significantly when the tolerance zone is defined as a cylinder. By defining the zone in this way, axis location is permitted to vary from its true defined as a cylinder. By defining the zone in this way, axis location is permitted to vary from its true position by an equal amount in all directions. In other words, the tolerance zone expands to include position by an equal amount in all directions. In other words, the tolerance zone expands to include areas that were previously unacceptable. In some instances, useable parts have been rejected because areas that were previously unacceptable. In some instances, useable parts have been rejected because the axis location of features was found to be outside the limits of coordinate tolerance boundaries—the axis location of features was found to be outside the limits of coordinate tolerance boundaries—but would have been within the circular limitsbut would have been within the circular limits ..


.014

.010

.010


Geometric (position) tolerancing allows the tolerance zone to be defined as a Geometric (position) tolerancing allows the tolerance zone to be defined as a cylindercylinder, , the diameter of which is equal to the the diameter of which is equal to the diagonal diagonal distancedistance across the corners of the across the corners of the coordinate tolerance zone. The previously unusable tolerance area increases the available coordinate tolerance zone. The previously unusable tolerance area increases the available tolerance by 57%!tolerance by 57%!



The 57% increase in usable tolerance (shaded areas) derived from geometric tolerancing, The 57% increase in usable tolerance (shaded areas) derived from geometric tolerancing, would not be acceptable in coordinate tolerancing situations. The small red crosses would not be acceptable in coordinate tolerancing situations. The small red crosses represent a few of the infinite number of possible axis locations that would be represent a few of the infinite number of possible axis locations that would be unacceptableunacceptable, using coordinate tolerancing, but which would be , using coordinate tolerancing, but which would be acceptableacceptable in position in position tolerancing. Consequently, geometric tolerancing. Consequently, geometric position tolerancingposition tolerancing –in appropriate applications— –in appropriate applications—has provided significant cost savings.has provided significant cost savings.


TRUE POSITION GEOMETRIC TRUE POSITION GEOMETRIC TOLERANCING TOLERANCING


True Position True Position is the is the exactexact or or perfectperfect location of a point, line or plane—usually the location of a point, line or plane—usually the center of a size feature—in relationship to a datum reference frame and/or other center of a size feature—in relationship to a datum reference frame and/or other features of size. features of size.

DEFINITIONDEFINITION


True Position ToleranceTrue Position Tolerance A specified area or zone, within which the center, axis, A specified area or zone, within which the center, axis, or center plane of a feature of size is permitted to vary from its theoretically exact or center plane of a feature of size is permitted to vary from its theoretically exact or ‘true’ position.or ‘true’ position.



True Position ToleranceTrue Position Tolerance A specified area or zone, within which the center, axis, A specified area or zone, within which the center, axis, or center plane of a feature of size is permitted to vary from its theoretically or center plane of a feature of size is permitted to vary from its theoretically exact or ‘true’ position.exact or ‘true’ position.

Note:Note: When features of size are controlled at MMC or LMC, the tolerance is When features of size are controlled at MMC or LMC, the tolerance is defined by the virtual condition boundarydefined by the virtual condition boundary, located at its theoretically exact , located at its theoretically exact position, which cannot be violated by surface elements of the controlled feature.position, which cannot be violated by surface elements of the controlled feature.



Basic Dimensions on DrawingsBasic Dimensions on Drawings

In the past, basic dimensions were labeled BASIC or BSC following or below the In the past, basic dimensions were labeled BASIC or BSC following or below the dimension (see MIL STD 8C; ANSI Y14.5-1973; ANSI Y14.5–1982). This dimension (see MIL STD 8C; ANSI Y14.5-1973; ANSI Y14.5–1982). This practice is no longer recommended.practice is no longer recommended.

3.438 BASIC

3.000 BSC



In the past, basic dimensions were labeled BASIC or BSC following or below the In the past, basic dimensions were labeled BASIC or BSC following or below the dimension (see MIL STD 8C; ANSI Y14.5-1973; ANSI Y14.5–1982). This dimension (see MIL STD 8C; ANSI Y14.5-1973; ANSI Y14.5–1982). This practice is no longer recommended.practice is no longer recommended.

Basic dimensions are (and were) also identified in a special symbol –an enclosing Basic dimensions are (and were) also identified in a special symbol –an enclosing rectangle:rectangle:** 24.6

** Current recommended practice ASME Y14.5M-1994Current recommended practice ASME Y14.5M-1994

3.438 BASIC

3.000 BSC



In the past, basic dimensions were labeled BASIC or BSC following or below the In the past, basic dimensions were labeled BASIC or BSC following or below the dimension (see MIL STD 8C; ANSI Y14.5 1973; ANSI Y14.5–1982). This dimension (see MIL STD 8C; ANSI Y14.5 1973; ANSI Y14.5–1982). This practice is no longer recommended.practice is no longer recommended.

Basic dimensions are (and were) also identified in a special symbol –an enclosing Basic dimensions are (and were) also identified in a special symbol –an enclosing rectangle:rectangle:**

They were also called out in special notes.They were also called out in special notes.**

24.6

** Current recommended practice ASME Y14.5M-1994Current recommended practice ASME Y14.5M-1994

3.438 BASIC

3.000 BSC

UNLESS OTHERWISE SPECIFIED, ALL UNTOLERANCED DIMENSIONS ARE BASIC


MMC BOUNDARY THEORYMMC BOUNDARY THEORY(INTERNAL FEATURES—HOLES)(INTERNAL FEATURES—HOLES)


Boundary TheoryBoundary Theory(Internal Features—Holes)(Internal Features—Holes)

Two center planes are necessary to Two center planes are necessary to identify the location of a hole. identify the location of a hole.



Basic dimensions locate the Basic dimensions locate the true true positionposition of the hole by locating the of the hole by locating the two required center planes from two required center planes from datum surfaces (or other features of datum surfaces (or other features of size that are, themselves, located size that are, themselves, located relative to a datum or datums).relative to a datum or datums).

True PositionTrue Position



A feature control frame is associated A feature control frame is associated with the size dimension of the hole, with the size dimension of the hole, and specifies the tolerance zone and specifies the tolerance zone (shape and size) for the feature—in (shape and size) for the feature—in this case a cylindrical tolerance zone this case a cylindrical tolerance zone for the axis of a hole.for the axis of a hole.

True PositionTrue PositionCylindrical Cylindrical Tolerance ZoneTolerance Zone



The theoretical boundary for the The theoretical boundary for the hole is determined by subtracting hole is determined by subtracting the position tolerance from the the position tolerance from the maximum material condition of maximum material condition of the hole sizethe hole size (this is also the virtual (this is also the virtual condition or VC of the hole).condition or VC of the hole). This This boundary is centered on the true boundary is centered on the true position.position.


Theoretical BoundaryTheoretical Boundary(Virtual Condition-(Virtual Condition-Hole at MMC – GTOL Tolerance)Hole at MMC – GTOL Tolerance)




Theoretical BoundaryTheoretical Boundary

(Actual Hole Diameter)(Actual Hole Diameter)

M

The The locationlocation of the hole axis may of the hole axis may vary within its cylindrical vary within its cylindrical tolerance limits (yellow circle), tolerance limits (yellow circle), but no element of the hole but no element of the hole surfacesurface may ever be may ever be insideinside the theoretical the theoretical boundary (blue-green circle). boundary (blue-green circle).






M

The series of slides that follow, The series of slides that follow, show various positions of the show various positions of the axis and resulting hole. Notice axis and resulting hole. Notice that the theoretical boundary is that the theoretical boundary is never violated.never violated.






M

Note that for every incremental Note that for every incremental change of axis location (always change of axis location (always located at an extreme position), located at an extreme position), the actual hole surface is the actual hole surface is outside the theoretical outside the theoretical boundary.boundary.






M



MMC BOUNDARY THEORYMMC BOUNDARY THEORY(EXTERNAL FEATURES—SHAFTS)(EXTERNAL FEATURES—SHAFTS)


MMC Boundary TheoryMMC Boundary Theory(External Features—Studs, Posts, Etc.)(External Features—Studs, Posts, Etc.)

The true position is located For an external feature.The true position is located For an external feature.




A cylindrical tolerance zone is established in the feature control frame.A cylindrical tolerance zone is established in the feature control frame.

CylindricalCylindricalToleranceToleranceZoneZone




The theoretical boundary is The theoretical boundary is established by adding the established by adding the maximum material condition maximum material condition value of the external feature value of the external feature to the positional toleranceto the positional tolerance, , and centering the resulting and centering the resulting boundary circle at the boundary circle at the true true positionposition. This value is also . This value is also the virtual condition of the the virtual condition of the external feature of size.external feature of size.


Theoretical BoundaryTheoretical Boundary(Virtual Condition – (Virtual Condition – Shaft at MMC + GTOL Tolerance)Shaft at MMC + GTOL Tolerance)






(Actual External Diameter)(Actual External Diameter)

M

The The locationlocation of the external feature axis of the external feature axis may vary within its cylindrical tolerance may vary within its cylindrical tolerance limits (yellow circle), but no elements of limits (yellow circle), but no elements of its its surface surface may be may be outsideoutside the theoretical the theoretical boundary blue-green circle). Let’s boundary blue-green circle). Let’s demonstrate that by cycling the pattern demonstrate that by cycling the pattern through a complete revolution.through a complete revolution.







M

The The locationlocation of the external feature of the external feature axis may vary within its cylindrical axis may vary within its cylindrical tolerance limits, but no elements of its tolerance limits, but no elements of its surface surface may be may be outsideoutside the theoretical the theoretical boundary. Let’s demonstrate that by boundary. Let’s demonstrate that by cycling the pattern through a complete cycling the pattern through a complete revolution.revolution.







M




TOLERANCE OF POSITIONTOLERANCE OF POSITIONREQUIREMENTSREQUIREMENTS


Position Tolerance RequirementsPosition Tolerance Requirements

• Wherever position tolerances are used, Wherever position tolerances are used, they must be applied to features of sizethey must be applied to features of size..

• Basic dimensions are usedBasic dimensions are used to locate and establish the absolute location or to locate and establish the absolute location or true positiontrue position of size features relative to specific datums and interrelated features. Basic dimensions of size features relative to specific datums and interrelated features. Basic dimensions are are notnot toleranced on the drawing. The absolute locations of features of size are toleranced on the drawing. The absolute locations of features of size are located by basic dimensions. Location tolerances for the size features are called out in located by basic dimensions. Location tolerances for the size features are called out in feature control frames.feature control frames.

• In most cases, In most cases, datum references are requireddatum references are required..


DATUM REFERENCES AND POSITION DATUM REFERENCES AND POSITION TOLERANCESTOLERANCES


Tolerance of Position applied RFSTolerance of Position applied RFS

Some fundamentals of position tolerancing, when applied regardless of Some fundamentals of position tolerancing, when applied regardless of feature size, are as follows:feature size, are as follows:

• The tolerance control is most often established around the feature axis or The tolerance control is most often established around the feature axis or center plane. center plane.

• No bonus tolerance is availableNo bonus tolerance is available because the stipulated tolerance applies at because the stipulated tolerance applies at any increment of size.any increment of size.

• Part verification requires the use of variable gages –usually at higher costPart verification requires the use of variable gages –usually at higher cost ..


TOLERANCE OF POSITION ATTOLERANCE OF POSITION ATREGARDLESS OF FEATURE SIZEREGARDLESS OF FEATURE SIZE


.490 - .500

C

A

B

.014 A B C

Tolerance of Position -- RFSTolerance of Position -- RFS

The information in the feature control The information in the feature control frame would be read as follows: frame would be read as follows: “Regardless of feature size, this feature “Regardless of feature size, this feature must be located on true position within must be located on true position within a cylindrical tolerance zone of .014 in. a cylindrical tolerance zone of .014 in. on diameter, with reference to datums on diameter, with reference to datums A (primary), B(secondary), and C A (primary), B(secondary), and C (tertiary).”(tertiary).”

Irrespective of how large or small the Irrespective of how large or small the actualactual hole size is—within its size hole size is—within its size limits—no additional tolerances are limits—no additional tolerances are available for the available for the locationlocation of the feature. of the feature. I’ll demonstrate in the next few slides. I’ll demonstrate in the next few slides.



Tolerance of Position -- RFSTolerance of Position -- RFSThe exact location of the hole is established with basic dimensions.The exact location of the hole is established with basic dimensions.




Location Tolerance Location Tolerance Zone –RFS Zone –RFS

The cylindrical tolerance zone is established in the feature control frame –(The cylindrical tolerance zone is established in the feature control frame –( .014). .014).

.014 A B C





.014 A B CFor the worst possible condition,For the worst possible condition,the hole axis is located at the the hole axis is located at the extreme limit of the cylindrical extreme limit of the cylindrical tolerance zone.tolerance zone.




Location Tolerance Location Tolerance Zone –RFS Zone –RFS (Always the Same)(Always the Same)

.014 A B C

MMC DiameterMMC Diameter

When the axis is located at the When the axis is located at the extreme limit of the tolerance extreme limit of the tolerance zone, the MMC holezone, the MMC hole axis would axis would be offset from the true position be offset from the true position by a distance equal to one-half by a distance equal to one-half of the position tolerance (.007). of the position tolerance (.007).





.014 A B C


The actual hole size may The actual hole size may vary between MMC vary between MMC (smallest diameter) and (smallest diameter) and LMC (largest diameter), LMC (largest diameter), but the but the axis locationaxis location cannot cannot violate the boundaries of violate the boundaries of its location tolerance.its location tolerance.

LMC DiameterLMC Diameter




Location Tolerance Location Tolerance Zone –RFSZone –RFS(Always the Same)(Always the Same)

.014 A B C



The white circle represents The white circle represents the MMC boundary. Its the MMC boundary. Its center is located at true center is located at true position. No element of the position. No element of the hole surface can be hole surface can be inside inside this boundary.this boundary.

MMC Boundary(VC Functional Gauge)





.014 A B C



The outer white circle The outer white circle represents the LMC represents the LMC boundary centered on boundary centered on true position. No true position. No elements on the surface elements on the surface of the hole can be of the hole can be outsideoutside of this of this boundary. The boundary. The following series of following series of slides will sequence the slides will sequence the progressive position of progressive position of the center of the hole as the center of the hole as it moves around the it moves around the tolerance zone.tolerance zone.

LMC BoundaryLMC Boundary






.014 A B C



The outer white circle The outer white circle represents the LMC represents the LMC boundary. No elements boundary. No elements on the surface of the on the surface of the hole can be hole can be outsideoutside of of this boundary. The this boundary. The following series of following series of slides will sequence the slides will sequence the progressive position of progressive position of the center of the hole as the center of the hole as it moves around the it moves around the tolerance zone.tolerance zone.







.014 A B C







TOLERANCE OF POSITION ATTOLERANCE OF POSITION ATMAXIMUM MATERIAL CONDITIONMAXIMUM MATERIAL CONDITION


The next example will illustrate the concept of bonus tolerance, in connection The next example will illustrate the concept of bonus tolerance, in connection with position tolerances. We will use the same drawing example that was used to with position tolerances. We will use the same drawing example that was used to discuss tolerances of position, when applied regardless of feature size (RFS). discuss tolerances of position, when applied regardless of feature size (RFS). One One of the significant differences you will see is the advantages of defining the of the significant differences you will see is the advantages of defining the tolerance zone for the axis of a hole as we did before—but this time, we will add tolerance zone for the axis of a hole as we did before—but this time, we will add the modifier for maximum material condition (MMC) to the tolerance the modifier for maximum material condition (MMC) to the tolerance specification in the feature control framespecification in the feature control frame. . Notice the changes that occur in Notice the changes that occur in location tolerances when modifiers are used, and as departure from MMC occurs.location tolerances when modifiers are used, and as departure from MMC occurs.

Tolerance of Position -- MMCTolerance of Position -- MMC


M

.490 - .500

.014 A B CC

A

B


The information in the feature The information in the feature control frame would be read as control frame would be read as follows: follows: “This feature must be “This feature must be located on true position within a located on true position within a cylindrical tolerance zone of .014 on cylindrical tolerance zone of .014 on diameter with reference to datums A diameter with reference to datums A (primary), B (secondary), and C (primary), B (secondary), and C (tertiary), when the hole is at its (tertiary), when the hole is at its smallest size, or MMC.”smallest size, or MMC.”

As the actual hole size increases in As the actual hole size increases in size from MMC, additional size from MMC, additional tolerance (equal to the amount of tolerance (equal to the amount of departure) may be departure) may be addedadded to the to the location tolerance for the feature.location tolerance for the feature.




The exact location of the hole is The exact location of the hole is established by basic dimensions.established by basic dimensions.



MMC Diameter (AxisMMC Diameter (Axisat Maximum Offset)at Maximum Offset)


The maximum material condition The maximum material condition diameter of .490 is shown at its diameter of .490 is shown at its maximum offset from true positionmaximum offset from true position—one-half the specified location —one-half the specified location tolerance.tolerance.



MMC DiameterMMC DiameterTolerance of Position -- MMCTolerance of Position -- MMC

As the size of the hole changes As the size of the hole changes within its tolerance range from within its tolerance range from MMC—smallest hole size MMC—smallest hole size limit, and increases in size limit, and increases in size towards the LMC, or upper towards the LMC, or upper size limit, an equal amount of size limit, an equal amount of tolerance can be tolerance can be addedadded to the to the axis axis locationlocation tolerance. tolerance.

Location Tolerance Location Tolerance Zone at LMCZone at LMC





The additional tolerance for The additional tolerance for the hole axis location (which is the hole axis location (which is equal to the amount of equal to the amount of departure from MMC), is departure from MMC), is called called “bonus tolerance.”“bonus tolerance.”

LMCLMCDiameterDiameter

Bonus Tolerance






When the hole size is at its When the hole size is at its lower limit (MMC), and lower limit (MMC), and positioned at the extreme positioned at the extreme limit of the MMC location limit of the MMC location tolerance, the MMC tolerance, the MMC boundary is established. boundary is established. When the feature of size is at When the feature of size is at this limit, no elements of the this limit, no elements of the hole hole surfacesurface may be inside may be inside this theoretical boundary. this theoretical boundary. This is the virtual condition This is the virtual condition of the hole, which also of the hole, which also simulates the mating part at simulates the mating part at its maximum material its maximum material conditioncondition..

MMC BoundaryMMC Boundary






MMC BoundaryMMC Boundary

When the hole size is at its When the hole size is at its upper limit (LMC), and upper limit (LMC), and positioned at the extreme positioned at the extreme limit of the location limit of the location tolerance, the LMC tolerance, the LMC boundary is boundary is established. established. No elements of No elements of the hole surfacethe hole surfacecan be out-side can be out-side this boundary.this boundary.







MMC BoundaryMMC Boundary(VC=MMC-Tol)(VC=MMC-Tol)


In this next series of slides, note In this next series of slides, note that while the size and location that while the size and location of the actual hole may vary, the of the actual hole may vary, the elements on elements on the surface of the holes the surface of the holes never violate their never violate their boundaries. This boundaries. This series will help series will help you to understand you to understand how the hole size how the hole size changes can affect changes can affect the location of the the location of the center axis—and its orientation.center axis—and its orientation.


Location Tolerance Location Tolerance at MMCat MMC

Location Tolerance at LMCLocation Tolerance at LMC







Axis location variance Axis location variance possibilities when position possibilities when position tolerance is modified to tolerance is modified to MMC.MMC.



ZERO POSITION TOLERANCE AT MMCZERO POSITION TOLERANCE AT MMC


Zero Position Tolerance at MMCZero Position Tolerance at MMC

Occasionally it may be desirable to Occasionally it may be desirable to increase position tolerancesincrease position tolerances, but , but maintain specific, albeit acceptable, feature size limits. Such can be maintain specific, albeit acceptable, feature size limits. Such can be achieved by calling out the lower limit of the hole size at the absolute achieved by calling out the lower limit of the hole size at the absolute minimum to allow a MMC fastener to be inserted, and specifying a MMC minimum to allow a MMC fastener to be inserted, and specifying a MMC position tolerance of zero.position tolerance of zero.


B

C

0 M A B C

(Min Hole=Max Fastener Fit)(Min Hole=Max Fastener Fit) A

When the holes are at MMC, When the holes are at MMC, the hole positions must be the hole positions must be exact. As the hole size moves exact. As the hole size moves towards LMC, the location towards LMC, the location tolerance increases tolerance increases proportionately.proportionately.

Zero Position Tolerance at MMCZero Position Tolerance at MMC


POSITION TOLERANCES POSITION TOLERANCES CONTROLLING PLANAR CONTROLLING PLANAR

APPLICATIONSAPPLICATIONS


Position Tolerances Controlling Planar Features of SizePosition Tolerances Controlling Planar Features of Size

Tolerance of position principles may also be applied to planar features of size, in Tolerance of position principles may also be applied to planar features of size, in which case, the diameter symbol is removed from the feature control frame. which case, the diameter symbol is removed from the feature control frame.

0.6 M A B C


Tolerance of position principles may also be applied to planar features of size, in Tolerance of position principles may also be applied to planar features of size, in which case, the diameter symbol is removed from the feature control frame.which case, the diameter symbol is removed from the feature control frame. The The resulting tolerance zone is established by resulting tolerance zone is established by two parallel planestwo parallel planes, separated by a distance , separated by a distance equal to the tolerance value. Modifiers, and therefore, bonus tolerances may also be equal to the tolerance value. Modifiers, and therefore, bonus tolerances may also be applied under these circumstances.applied under these circumstances.

0.6 M A B C

Position Tolerances Controlling Planar Features of SizePosition Tolerances Controlling Planar Features of Size


N

R

20.520.0

8.88.0

0.4 R N

Let’s consider Let’s consider controlling symmetry of a feature of size, using position tolerancingcontrolling symmetry of a feature of size, using position tolerancing. The . The tolerance must be maintained regardless of feature size. A feature of size dimension tolerance must be maintained regardless of feature size. A feature of size dimension (20.0-20.5mm), establishes datum centerplane N. Regardless of feature size, the (20.0-20.5mm), establishes datum centerplane N. Regardless of feature size, the centerplane of the controlled centerplane of the controlled groovegroove must be within two parallel planes, 0.4 mm apart, must be within two parallel planes, 0.4 mm apart, that is centered on datum plane N and perpendicular to datum plane R.that is centered on datum plane N and perpendicular to datum plane R.

Symmetrical Features ControlledSymmetrical Features ControlledWith Position Tolerancing -- RFSWith Position Tolerancing -- RFS


Two parallel planes,Two parallel planes,0.4 mm apart.0.4 mm apart.

N

R

20.520.0

0.4 R N

In other words, the centerplane of the groove (and its mating envelope) must lie between In other words, the centerplane of the groove (and its mating envelope) must lie between two parallel planes 0.4 apart. These two planes must be perpendicular to datum plane R two parallel planes 0.4 apart. These two planes must be perpendicular to datum plane R and be equally disposed about datum plane N. and be equally disposed about datum plane N.

Symmetrical Features ControlledSymmetrical Features ControlledWith Position Tolerancing -- RFSWith Position Tolerancing -- RFS

Mating EnvelopeMating Envelope


Datum centerplane K is established by the feature of size dimension 20.0-20.5 mm. Datum centerplane K is established by the feature of size dimension 20.0-20.5 mm. The centerplane of the groove on the right side must be within a 0.2 mm tolerance The centerplane of the groove on the right side must be within a 0.2 mm tolerance zone, consisting of two parallel planes 0.2 mm apart.zone, consisting of two parallel planes 0.2 mm apart.

Symmetrical Features ControlledSymmetrical Features ControlledWith Position Tolerancing at With Position Tolerancing at MMCMMC

J

20.520.0

K

8.88.4

0.2 M J K M


Two parallel planes,Two parallel planes,0.2 mm apart.0.2 mm apart.

J

20.520.0

K

8.88.4

0.2 M J K M

Symmetrical Features ControlledSymmetrical Features ControlledWith Position Tolerancing at MMCWith Position Tolerancing at MMC

When the controlled groove size is at MMC, it must be positioned or located about the When the controlled groove size is at MMC, it must be positioned or located about the centerplane of datum feature K within 0.2 mm,. As departure from the MMC occurs, centerplane of datum feature K within 0.2 mm,. As departure from the MMC occurs, additional tolerance is available—up to the limits of the groove size tolerance (0.4). The additional tolerance is available—up to the limits of the groove size tolerance (0.4). The groove centerplane must also be perpendicular to planar datum J within 0.2 mm at MMC. groove centerplane must also be perpendicular to planar datum J within 0.2 mm at MMC. As the datum feature size varies within its tolerance zone, greater flexibility is available.As the datum feature size varies within its tolerance zone, greater flexibility is available.


DATUM KDATUM KFEATUREFEATURESIZESIZE

20.5

8.4 8.5 8.6 8.7 8.8

20.4

20.3

20.2

20.1

20.0

Width ofWidth ofToleranceToleranceZoneZone

J

20.520.0

K

8.88.4

0.2 M J K M

GROOVE FEATURE SIZEGROOVE FEATURE SIZE

The chart shows the values of size that would occur as the height of the The chart shows the values of size that would occur as the height of the object, object, and and the groove size depart from MMC towards LMC. the groove size depart from MMC towards LMC.

Symmetrical Features ControlledSymmetrical Features ControlledWith Position Tolerancing at MMCWith Position Tolerancing at MMC

0.2 0.3 0.4 0.5 0.6

0.3 0.4 0.5 0.6 0.7

0.4 0.5 0.6 0.7 0.8

0.5 0.6 0.7 0.8 0.9

0.6 0.7 0.8 0.9 1.0

0.7 0.8 0.9 1.0 1.1

MMC

LMC


POSITIONING MULTIPLE POSITIONING MULTIPLE SYMMETRICAL FEATURES AT MMCSYMMETRICAL FEATURES AT MMC


• Dimension relationships between features, establish the size specifications and Dimension relationships between features, establish the size specifications and the number of times the features occur in the part.the number of times the features occur in the part.

• Identify and label all related and controlling datums.Identify and label all related and controlling datums.

• Complete the specification with the position tolerance, including appropriate Complete the specification with the position tolerance, including appropriate references to the related datums, in the feature control frame.references to the related datums, in the feature control frame.

Position Tolerancing, Used to Locate Tabs and/or Slots That Position Tolerancing, Used to Locate Tabs and/or Slots That Are Symmetrical About Their Center PlanesAre Symmetrical About Their Center Planes


Locating Symmetrical FeaturesLocating Symmetrical Features

Dimension locations and relationships between features, and specify the number of instances followed Dimension locations and relationships between features, and specify the number of instances followed by the size specification.by the size specification.

8X 6.0 - 6.2

25 00.4

52 00.6

400.4 0

8X 45º



Identify and label related datumsIdentify and label related datums

D

25 00.4

8X 6.0 - 6.2

25 00.4

52 00.6

400.4 0

E

8X 45º


0.5 M D E M

8X 45º D

25 00.4

8X 6.0 - 6.2

25 00.4

52 00.6

400.4 0

E


Complete the specification with the position tolerance, including appropriate references to Complete the specification with the position tolerance, including appropriate references to the related datums, in the feature control frame.the related datums, in the feature control frame.


NONPARALLEL FEATURESNONPARALLEL FEATURES


Nonparallel FeaturesNonparallel Features

Occasionally, holes must be placed at an angle to a surface. There are also Occasionally, holes must be placed at an angle to a surface. There are also instances where the axes of holes may not be parallel to each other --such as a instances where the axes of holes may not be parallel to each other --such as a pattern of holespattern of holes around the outside of a cylinder. Position tolerances may be used around the outside of a cylinder. Position tolerances may be used in these circumstances to properly locate and position features relative to each in these circumstances to properly locate and position features relative to each other, and to a datum or datums. other, and to a datum or datums.


4X 45º12

20

A

75.275.0

8X 45º

8X 8+ 0.2 0

4X 10 + 0.2 0

0.2 M A B M

0.4 M A B MB

Angled and Nonparallel FeaturesAngled and Nonparallel Features

A

A

SECTION A–A


POSITION TOLERANCES AT LMCPOSITION TOLERANCES AT LMC


Position Tolerances at LMCPosition Tolerances at LMC

When a LMC modifier is applied to a tolerance of position, When a LMC modifier is applied to a tolerance of position, the tolerance applies the tolerance applies when the least amount of material is left in the partwhen the least amount of material is left in the part (largest hole, smallest shaft). (largest hole, smallest shaft).

Conditions are reversed from the MMC control. Conditions are reversed from the MMC control. There is no bonus tolerance There is no bonus tolerance when the feature of size is at LMC, and the full bonus tolerance is available at when the feature of size is at LMC, and the full bonus tolerance is available at MMC. MMC.



The least material condition modifier is commonly used to The least material condition modifier is commonly used to

Control minimum wall thicknessControl minimum wall thickness on a part, on a part,

Maintain a minimum distanceMaintain a minimum distance from an edge to a feature such as a hole, or from an edge to a feature such as a hole, or

Control minimum stockControl minimum stock for machining on castings. for machining on castings.

Variable gaging or open inspectionVariable gaging or open inspection techniques are required for verification. techniques are required for verification.


True positionTrue positionTrue positionTrue position

True position is determined by basic dimensions, and the tolerance is depicted at True position is determined by basic dimensions, and the tolerance is depicted at the maximum diameter limit—(LMC).the maximum diameter limit—(LMC).


Tolerance zone at LMCTolerance zone at LMC





Hole size at maximum diameter (LMC)Hole size at maximum diameter (LMC)

Locating the LMC diameter Locating the LMC diameter of the hole with its axis at the of the hole with its axis at the extreme offset from true extreme offset from true position, we represent the position, we represent the worst position for wall worst position for wall thickness or distance spacing thickness or distance spacing control from a datum surface.control from a datum surface.






The location tolerance zone The location tolerance zone increasesincreases in an amount equal in an amount equal to the departure of the hole to the departure of the hole size away from LMC (size away from LMC (as the as the hole gets smallerhole gets smaller).).






The least material condition The least material condition (largest hole size) is (largest hole size) is specified because the specified because the minimum wall thickness, or minimum wall thickness, or distance from the edge of distance from the edge of the hole to the edge of the the hole to the edge of the part must be controlled.part must be controlled.

As the hole gets smaller, the As the hole gets smaller, the actual location of the hole actual location of the hole becomes less critical.becomes less critical. Therefore, bonus tolerance Therefore, bonus tolerance allows for an increase in allows for an increase in offset tolerance for the axis offset tolerance for the axis of the hole from its true of the hole from its true position.position.



This next series of slides present an example problem and solution, dealing with This next series of slides present an example problem and solution, dealing with least material condition. There is a minimum of text associate with each slide. least material condition. There is a minimum of text associate with each slide. Take the time to study the presentation, however, and you will discover that the Take the time to study the presentation, however, and you will discover that the affects of LMC, in a position context, is calculated just the opposite of the affects affects of LMC, in a position context, is calculated just the opposite of the affects of MMC. When minimum edge distance or minimum wall thickness is important, of MMC. When minimum edge distance or minimum wall thickness is important, least material condition should likely be considered.least material condition should likely be considered.

It is important to remember that when a position tolerance is modified to apply at It is important to remember that when a position tolerance is modified to apply at least material condition (LMC), all of the principles of MMC are essentially least material condition (LMC), all of the principles of MMC are essentially reversed. Bonus tolerances do apply, but they are maximized when the feature of reversed. Bonus tolerances do apply, but they are maximized when the feature of size is at MMC. At least material condition, there is no bonus tolerance.size is at MMC. At least material condition, there is no bonus tolerance.


25.4 - 25.6

0.4 L A 12.0 - 12.2

A54.0 - 54.2

L

Calculating Least Material ConditionCalculating Least Material Condition

This is a hollow step shaft. A minimum wall thickness of 6.0 mm must be This is a hollow step shaft. A minimum wall thickness of 6.0 mm must be assured. assured.


Expanding pin or mandrel establishes datum axis AExpanding pin or mandrel establishes datum axis A

25.4 - 25.6

0.4 L A 12.0 - 12.2

A54.0 - 54.2

L

Datum A is first established using a variable gage.Datum A is first established using a variable gage.


25.4 LMC


Expanding mandrel establishes datum axis AExpanding mandrel establishes datum axis A

0.4 (Cylindrical) Zone0.4 (Cylindrical) Zone

25.4 - 25.6

0.4 L A 12.0 - 12.2

A54.0 - 54.2

L

The axis of the internal diameter must be within a cylindrical tolerance zone 0.4 mm in diameter. The axis of the internal diameter must be within a cylindrical tolerance zone 0.4 mm in diameter.


25.4 LMC




25.4 LMC

25.4 - 25.6

0.4 L A 12.0 - 12.2

A54.0 - 54.2

L

25.0 Theoretical25.0 Theoretical BoundaryBoundary

The position tolerance is subtracted from the LMC of the internal diameter, resulting in a diameter of The position tolerance is subtracted from the LMC of the internal diameter, resulting in a diameter of 25.0 mm, and producing the critical size limit or boundary--25.0 mm, and producing the critical size limit or boundary-- 25.0 mm. 25.0 mm.



6.4 Minimum wall6.4 Minimum wall



25.4 - 25.6

0.4 L A 12.0 - 12.2

A54.0 - 54.2

L

25.0 Theoretical25.0 Theoretical BoundaryBoundary

25.4 LMC

The upper limit of the hole diameter is 12.2 mm. Subtract this amount from the lower limit The upper limit of the hole diameter is 12.2 mm. Subtract this amount from the lower limit of the outside diameter (25.0 – 12.2 = 12.8/2 = 6.4 mm minimum wall thickness).of the outside diameter (25.0 – 12.2 = 12.8/2 = 6.4 mm minimum wall thickness).



25.4 - 25.6

0.4 L A 12.0 - 12.2

A54.0 - 54.2

L

25.0 Theoretical25.0 Theoretical BoundaryBoundary6.4 Minimum wall6.4 Minimum wall



25.4 LMC

25.425.4 LMCLMC - .4- .4 Tol ZoneTol Zone= 25.0 (VC) 25.0 (VC) - 12.2- 12.2 LMC of ‘A’ LMC of ‘A’ 12.812.8 22 Rad. FactorRad. Factor= 6.4 6.4 Min WallMin Wall

Go through the process again. Make sure you understand what is being done in this Go through the process again. Make sure you understand what is being done in this calculation.calculation.



COMPOSITE POSITION TOLERANCINGCOMPOSITE POSITION TOLERANCING


Composite Position TolerancingComposite Position Tolerancing

When features such as holes are arranged in a pattern, and the location of the When features such as holes are arranged in a pattern, and the location of the pattern is less significant to the design than the actual relationships between the pattern is less significant to the design than the actual relationships between the holes in the pattern (position and orientation), composite position tolerancing holes in the pattern (position and orientation), composite position tolerancing should be considered.should be considered.

A A Pattern-locating Tolerance Zone FrameworkPattern-locating Tolerance Zone Framework (PLTZF) controls the location of (PLTZF) controls the location of the hole pattern.the hole pattern.

PLTZF M X Y Z0.4



When features such as holes are arranged in a pattern, and the location of the When features such as holes are arranged in a pattern, and the location of the pattern is less significant to the design than the actual relationships between the pattern is less significant to the design than the actual relationships between the holes in the pattern (position and orientation), composite position tolerancing holes in the pattern (position and orientation), composite position tolerancing should be considered.should be considered.

A A Pattern-locating Tolerance Zone FrameworkPattern-locating Tolerance Zone Framework (PLTZF) controls the location of (PLTZF) controls the location of the hole pattern.the hole pattern.

A A Feature-relating Tolerance Zone FrameworkFeature-relating Tolerance Zone Framework (FRTZF) establishes the (FRTZF) establishes the interrelationships between features.interrelationships between features.

PLTZFFRTZF

M X Y ZM X

0.4

0.15



The pattern-locating tolerance zone framework (PLTZF) is always located relative The pattern-locating tolerance zone framework (PLTZF) is always located relative to specific datums, using basic dimensions.to specific datums, using basic dimensions.

The PLTZF calls out the larger position tolerance to locate the pattern of features The PLTZF calls out the larger position tolerance to locate the pattern of features as a group.as a group.

The PLTZF is always specified in the upper segment of the feature control frame, The PLTZF is always specified in the upper segment of the feature control frame, and establishes the order of precedence for inspection and verification.and establishes the order of precedence for inspection and verification.



The pattern-locating tolerance zone framework (PLTZF) is always located relative The pattern-locating tolerance zone framework (PLTZF) is always located relative to specific datums, using basic dimensions.to specific datums, using basic dimensions.

The PLTZF calls out the larger position tolerance to locate the pattern of features The PLTZF calls out the larger position tolerance to locate the pattern of features as a group.as a group.

The PLTZF is always specified in the upper segment of the feature control frame, The PLTZF is always specified in the upper segment of the feature control frame, and establishes the order of precedence for inspection and verification.and establishes the order of precedence for inspection and verification.

M X Y Z0.4



The feature-relating tolerance zone framework (FRTZF) controls the feature The feature-relating tolerance zone framework (FRTZF) controls the feature interrelationships within the pattern of features.interrelationships within the pattern of features.

The FRTZF resides in the lower half of the feature control frame and establishes a smaller The FRTZF resides in the lower half of the feature control frame and establishes a smaller position tolerance, controlling the relationships of features to each other, position tolerance, controlling the relationships of features to each other, withinwithin the located the located pattern (PLTZFpattern (PLTZF).).

Basic dimensions used to relate the PLTZF to controlling datums do not apply to the FRTZF.Basic dimensions used to relate the PLTZF to controlling datums do not apply to the FRTZF.

Datum references may be applied, but are not required in the FRTZF. In the example, the Datum references may be applied, but are not required in the FRTZF. In the example, the orientation (attitude) of the features is controlled with reference to datum X, but with no orientation (attitude) of the features is controlled with reference to datum X, but with no relationship to datums Y and Z.relationship to datums Y and Z.



The The feature-relating tolerance zone framework (FRTZF)feature-relating tolerance zone framework (FRTZF) controls the feature controls the feature interrelationships within the pattern of features.interrelationships within the pattern of features.

The FRTZF resides in the lower half of the feature control frame and establishes a smaller The FRTZF resides in the lower half of the feature control frame and establishes a smaller position tolerance, controlling the relationships of features to each other, within the located position tolerance, controlling the relationships of features to each other, within the located pattern (PLTZF).pattern (PLTZF).

Basic dimensions used to relate the PLTZF to controlling datums do not apply to the FRTZF.Basic dimensions used to relate the PLTZF to controlling datums do not apply to the FRTZF.

Datum references may be applied, but are not required in the FRTZF. In the example, the Datum references may be applied, but are not required in the FRTZF. In the example, the orientation (attitude) of the features is controlled with reference to datum X, but with no orientation (attitude) of the features is controlled with reference to datum X, but with no relationship to datums Y and Z.relationship to datums Y and Z.

M X Y ZM X

0.4

0.15


Composite and Single-Segment Feature Control FramesComposite and Single-Segment Feature Control FramesWe will consider the four-hole pattern that is controlled with a We will consider the four-hole pattern that is controlled with a compositecomposite feature control feature control frame. Note that the three holes near the base of the part are controlled with twoframe. Note that the three holes near the base of the part are controlled with two single-single-line feature control framesline feature control frames. . This practice is followed when it is necessary to apply the This practice is followed when it is necessary to apply the basic dimensions along with the datum references for both thebasic dimensions along with the datum references for both the pattern locatingpattern locating and the and the feature relatingfeature relating tolerances (PLTZF and FRTZF). tolerances (PLTZF and FRTZF).

X

Z

Y

0.4 M X Y ZX0.15 M

M X Y ZM X Y Z

0.40.1


X

Z

Y

0.4 M X Y ZX0.15 M

M X Y ZM X Y Z

0.40.1

Composite Feature Control FramesComposite Feature Control FramesLet’s examine the four-hole pattern at the top of the part. An enlarged view may help us Let’s examine the four-hole pattern at the top of the part. An enlarged view may help us evaluate the interaction between the PLTZF and the FRTZF—controls for the location of the evaluate the interaction between the PLTZF and the FRTZF—controls for the location of the hole pattern, and the interrelationships between holes in the pattern. This single, composite hole pattern, and the interrelationships between holes in the pattern. This single, composite feature control frame has a very specific application.feature control frame has a very specific application.


M X Y Z0.4

X0.15 M

Composite Feature Control FramesComposite Feature Control FramesThe four-hole pattern must be located as a group from datums X, Y, and Z, with each hole The four-hole pattern must be located as a group from datums X, Y, and Z, with each hole having a cylindrical tolerance zone, 0.4 mm in diameter (PLTZF). The holes must be having a cylindrical tolerance zone, 0.4 mm in diameter (PLTZF). The holes must be positionedpositioned relative to each other relative to each other within a cylindrical zone 0.15 mm in diameter (FRTZF), within a cylindrical zone 0.15 mm in diameter (FRTZF), and fully within the larger pattern-locating tolerance zone. The holes will also be and fully within the larger pattern-locating tolerance zone. The holes will also be perpendicular to datum feature X within 0.15.perpendicular to datum feature X within 0.15.


Composite Feature Control FramesComposite Feature Control FramesThe theoretically exact hole pattern location is positioned with basic dimensions The theoretically exact hole pattern location is positioned with basic dimensions with reference to datums X, Y, and Z.with reference to datums X, Y, and Z.

M X Y Z0.4

X0.15 M


0.4 tolerance zone 0.4 tolerance zone (PLTZF)(PLTZF)

M X Y Z0.4

X0.15 M

The cylindrical tolerance zones (shown in yellow) for the pattern locating The cylindrical tolerance zones (shown in yellow) for the pattern locating tolerance zone is located at the pattern’s true position.tolerance zone is located at the pattern’s true position.

Composite Feature Control FramesComposite Feature Control Frames



M X Y Z0.4

X0.15 M

The cylindrical tolerance zones (shown in yellow) for the pattern locating The cylindrical tolerance zones (shown in yellow) for the pattern locating tolerance zone is located at the pattern’s true position. tolerance zone is located at the pattern’s true position. The small crosses The small crosses represent a possible displacement of the axes, but still within the tolerance zones.represent a possible displacement of the axes, but still within the tolerance zones.




M X Y Z0.4

X0.15 M

The misalignment is more obvious with the center planes displayed. Note that the The misalignment is more obvious with the center planes displayed. Note that the axis location for each hole is within the prescribed location tolerance zone for the axis location for each hole is within the prescribed location tolerance zone for the pattern of holes.pattern of holes.




M X Y Z0.4

X0.15 M

The The feature relating tolerance zonefeature relating tolerance zone is shown within the larger pattern locating is shown within the larger pattern locating tolerance zone, on the drawing layout. Note that the feature related tolerance tolerance zone, on the drawing layout. Note that the feature related tolerance zones are zones are mostlymostly within the pattern location tolerance zones. within the pattern location tolerance zones.


0.15 0.15 tolerance zonestolerance zones(FRTZF)(FRTZF)



M X Y Z0.4


0.15 0.15 tolerance zonestolerance zones(FRTZF)(FRTZF)

Feature axes must lie within Feature axes must lie within bothboth tolerance zone cylinders simultaneously. Portions of the tolerance zone cylinders simultaneously. Portions of the feature relating tolerance zones are not available if they extend outside the boundaries of the feature relating tolerance zones are not available if they extend outside the boundaries of the pattern locating tolerance zones. pattern locating tolerance zones. Parts with hole axes outside the areas included within Parts with hole axes outside the areas included within bothboth circles would be rejected.circles would be rejected.

X0.15 M



The feature axis may be anywhere within the area shared by The feature axis may be anywhere within the area shared by bothboth inscribing tolerance zones. Any area of the combined inscribing tolerance zones. Any area of the combined tolerance zones that is not included within tolerance zones that is not included within bothboth circles is sacrificed. In this case, to be accepted, the feature axis could circles is sacrificed. In this case, to be accepted, the feature axis could not be within the red portion of the blue circle (FRTZF). It must be in the area shared by both zones, as shown.not be within the red portion of the blue circle (FRTZF). It must be in the area shared by both zones, as shown.


ALIGNMENT OF COAXIAL FEATURESALIGNMENT OF COAXIAL FEATURES


Coaxial Feature AlignmentCoaxial Feature AlignmentCase Number OneCase Number One

When multiple aligned holes (located as a group) are to be on a controlled linear When multiple aligned holes (located as a group) are to be on a controlled linear axis, a composite position tolerance may be used. axis, a composite position tolerance may be used.

The pattern locating tolerance zone framework (PLTZF—located on top in the The pattern locating tolerance zone framework (PLTZF—located on top in the composite feature control frame) is a larger cylindrical tolerance, extending composite feature control frame) is a larger cylindrical tolerance, extending through the part, within which the holes must lie as a group.through the part, within which the holes must lie as a group.

The smaller cylindrical feature relating tolerance zone framework (FRTZF—the The smaller cylindrical feature relating tolerance zone framework (FRTZF—the bottom segment in the feature control frame) controls the feature to feature bottom segment in the feature control frame) controls the feature to feature alignment within the pattern locating tolerance boundary (PLTZF).alignment within the pattern locating tolerance boundary (PLTZF).


Linear Coaxial Feature AlignmentLinear Coaxial Feature Alignment

3X 6 + 0.2 0

A

B

0.4 M

0.1 M

A B

A B

The three-hole linear pattern on this hinge is to The three-hole linear pattern on this hinge is to be located on true position with reference to be located on true position with reference to datum features A and B within a cylindrical datum features A and B within a cylindrical tolerance of 0.4 mm diameter at MMC.tolerance of 0.4 mm diameter at MMC.

Datum Reference in the PLTZFDatum Reference in the PLTZF


Datum Reference in the FRTZFDatum Reference in the FRTZF

3X 6 + 0.2 0

A

B

0.4 M

0.1 M

A B

A B

The features are to be The features are to be alignedaligned in relation to in relation to each each otherother with reference to datum features A and B with reference to datum features A and B within a cylindrical tolerance of 0.1 diameter at within a cylindrical tolerance of 0.1 diameter at MMC, which must be MMC, which must be withinwithin the larger pattern the larger pattern locating tolerance of 0.4 diameter.locating tolerance of 0.4 diameter.



0.4 M

0.1 M

A B

A B


First, let’s examine the affect of the PLTZF. A cylindrical tolerance zone, 0.4 mm First, let’s examine the affect of the PLTZF. A cylindrical tolerance zone, 0.4 mm in diameter, is specified for the three aligned holes. The axis of all three holes in diameter, is specified for the three aligned holes. The axis of all three holes must be within this tolerance zone.must be within this tolerance zone.


0.4 M

0.1 M

A B

A B


Notice that in this case, both the PLTZF and the FRTZF have reference to datums A Notice that in this case, both the PLTZF and the FRTZF have reference to datums A and B. The outcome of this requirement will be considered in the next few slides.and B. The outcome of this requirement will be considered in the next few slides.

3X 6+ 0.2 0

A

B

0.4 M

0.1 M

A B

A B


0.4 M

0.1 M

A B

A B


The The feature relatingfeature relating tolerance is depicted as red cylindrical zone in the drawing. Note tolerance is depicted as red cylindrical zone in the drawing. Note that they are that they are centeredcentered within the boundaries of the larger pattern locating tolerance zone. within the boundaries of the larger pattern locating tolerance zone. The axis of the holes may be anywhere within these boundaries, but must be held, in The axis of the holes may be anywhere within these boundaries, but must be held, in terms of their position and orientation, with regard to datums A and B.terms of their position and orientation, with regard to datums A and B.


0.4 M

0.1 M

A B

A B


This illustration depicts the worst case for alignment of the axes and the three This illustration depicts the worst case for alignment of the axes and the three holes. The hole axes must be within the red tolerance zones which are positioned holes. The hole axes must be within the red tolerance zones which are positioned relative to datums A and B.relative to datums A and B.


0.4 M

0.1 M

A B

A B


At MMC, the hinge pin will still slide through the three holes without At MMC, the hinge pin will still slide through the three holes without interference.interference.


Coaxial Feature AlignmentCoaxial Feature Alignment

In this next series of slides, the example will depict a situation where no In this next series of slides, the example will depict a situation where no orientation datum features are identified in the feature relating tolerance zone orientation datum features are identified in the feature relating tolerance zone framework—the lower portion of the composite feature control frame or FRTZF. framework—the lower portion of the composite feature control frame or FRTZF. The refining (FRTZF) tolerance controls the feature to feature alignment within The refining (FRTZF) tolerance controls the feature to feature alignment within the larger pattern location position tolerance (PLTZF), without regard to the the larger pattern location position tolerance (PLTZF), without regard to the locating datums.locating datums.


3X 6 + 0.2 0

A

B

0.4 M

0.1 M

A B

The circumstances in this case are similar to the last The circumstances in this case are similar to the last example, with one major difference. Notice that the FRTZF example, with one major difference. Notice that the FRTZF (the lower segment of the feature control frame) contains no (the lower segment of the feature control frame) contains no datum references. The results of this type of control will be datum references. The results of this type of control will be illustrated in the next few slides.illustrated in the next few slides.



3X 6 + 0.2 0

A

B

0.4 M

0.1 M

A B


The three-hole linear pattern is to be located on true position with reference to The three-hole linear pattern is to be located on true position with reference to datum features A and B within a cylindrical tolerance of 0.4 diameter at MMC.datum features A and B within a cylindrical tolerance of 0.4 diameter at MMC.


No Datum Reference in the FRTZFNo Datum Reference in the FRTZF

3X 6 + 0.2 0

A

B

0.4 M

0.1 M

A B


The features are to be aligned in relation to The features are to be aligned in relation to each othereach other without reference to datum features A and B within a without reference to datum features A and B within a cylindrical tolerance of 0.1 diameter at MMC, which must be cylindrical tolerance of 0.1 diameter at MMC, which must be within the larger pattern locating tolerance of 0.4 diameter.within the larger pattern locating tolerance of 0.4 diameter.


0.4 M

0.1 M

A B


The limits of the pattern locating tolerance zone are illustrated below. They The limits of the pattern locating tolerance zone are illustrated below. They position the three holes within the 0.4mm diameter cylindrical tolerance that position the three holes within the 0.4mm diameter cylindrical tolerance that extends through the part.extends through the part.


0.4 M

0.1 M

A B

The feature relating tolerance zone (shown in red) must contain the axes for the The feature relating tolerance zone (shown in red) must contain the axes for the three holes. Note that in this case, the feature relating tolerance zone is three holes. Note that in this case, the feature relating tolerance zone is notnot centered on the axis of the pattern locating tolerance zone. However, the total centered on the axis of the pattern locating tolerance zone. However, the total feature relating tolerance zone (extended across the part) cannot violate the extents feature relating tolerance zone (extended across the part) cannot violate the extents of the pattern locating tolerance zone.of the pattern locating tolerance zone.



0.4 M

0.1 M

A B

The axes and holes are shown in their worst case position and orientation. The The axes and holes are shown in their worst case position and orientation. The pattern locating tolerance zone is maintained with respect to the controlling datums. pattern locating tolerance zone is maintained with respect to the controlling datums. However, the feature relating tolerance zone has been free to float within the larger However, the feature relating tolerance zone has been free to float within the larger locating zone. The hinge pin will still fit into the holes, but it will not be directly locating zone. The hinge pin will still fit into the holes, but it will not be directly linked to datums A and B.linked to datums A and B.



0.4 M

0.1 M

A B

Linear Coaxial Feature AlignmentLinear Coaxial Feature AlignmentIn essence, what has been specified, is that the orientation and position of the hinge In essence, what has been specified, is that the orientation and position of the hinge pin—relative to datums A and B—is less critical to the success of the design, than pin—relative to datums A and B—is less critical to the success of the design, than the position of the linear the position of the linear coaxial patterncoaxial pattern of the holes. The part will still function as of the holes. The part will still function as intended, even though the coaxiality of the feature relationships are not linked intended, even though the coaxiality of the feature relationships are not linked directly to the controlling datums.directly to the controlling datums.


If the holes are different sizes, their diameters must be called out in appropriate views.If the holes are different sizes, their diameters must be called out in appropriate views.

The feature alignment requirements are identified in the composite feature control The feature alignment requirements are identified in the composite feature control frame.frame.

Place a note below the feature control frame to indicate the extent of the control. For Place a note below the feature control frame to indicate the extent of the control. For example: TWO COAXIAL HOLES.example: TWO COAXIAL HOLES.



A

B

Different Size HolesDifferent Size Holes

10.0 - 10.25.0 - 5.2

TWO COAXIAL HOLES

0.6 M

0.3 M

A B

Similar to the last example, the feature relationship is not held relative to the Similar to the last example, the feature relationship is not held relative to the datums, but is controlled relative to the limits of the cylindrical tolerance datums, but is controlled relative to the limits of the cylindrical tolerance formed by the formed by the pattern location and coaxial requirementspattern location and coaxial requirements. The holes are . The holes are different sizes, but they must be aligned axially—within both acceptable different sizes, but they must be aligned axially—within both acceptable tolerance zones.tolerance zones.

Coaxial Feature AlignmentCoaxial Feature Alignment


COUNTERBORED HOLESCOUNTERBORED HOLES


Counterbored HolesCounterbored Holes

If the location, datum references, and position tolerance for a counterbore axis is If the location, datum references, and position tolerance for a counterbore axis is to be the same as the axis of the hole, only one feature control frame is used.to be the same as the axis of the hole, only one feature control frame is used.

If the position tolerance of the counterbore axis is not required to be the same as If the position tolerance of the counterbore axis is not required to be the same as the hole, then individual callouts may be used –one for the hole, the other for the the hole, then individual callouts may be used –one for the hole, the other for the counterbore.counterbore.


0.2 M A B C

A

B

C

4X 5.4 - 5.68.4 - 8.6

5.0 - 5.5

Counterbored HolesCounterbored HolesIn this example, both the clearance hole and the counterbore specification are controlled with a single geometric tolerance In this example, both the clearance hole and the counterbore specification are controlled with a single geometric tolerance for position.for position.


Counterbored HolesCounterbored HolesThe interpretation of the previous slide indicates that the position of the hole and The interpretation of the previous slide indicates that the position of the hole and the counterbore are on the same axis—located on true position relative to the the counterbore are on the same axis—located on true position relative to the prescribed datums.prescribed datums.

0.2 cylindrical tolerance zone --for 0.2 cylindrical tolerance zone --for bothboth the hole and the counterbore the hole and the counterbore


Datum Plane ADatum Plane A




A

B

C

Counterbored HolesCounterbored HolesIn this example, the clearance hole and the counterbore specifications are controlled with In this example, the clearance hole and the counterbore specifications are controlled with separateseparate and and featurefeature--specificspecific geometric tolerances for location.geometric tolerances for location.

4X 5.4 - 5.6

8.4 - 8.6 5.0 - 5.5

0.2 M A B C

0.5 M A B C


By interpretation, the axis tolerance for the clearance hole is separate from the By interpretation, the axis tolerance for the clearance hole is separate from the axis tolerance for the counterbore. The function of each is the determining factor axis tolerance for the counterbore. The function of each is the determining factor in this type of decision.in this type of decision.





0.2 cylindrical tolerance0.2 cylindrical tolerancezone for the hole at MMCzone for the hole at MMC

0.5 cylindrical0.5 cylindricaltolerance zone fortolerance zone forcounterbore at MMCcounterbore at MMC



For each of the clearance hole and counterbore, there is a separate tolerance zone For each of the clearance hole and counterbore, there is a separate tolerance zone specified. If it is necessary to perform these functions separately, this procedure specified. If it is necessary to perform these functions separately, this procedure may save costs. If, however, the operations are done simultaneously, tool changes may save costs. If, however, the operations are done simultaneously, tool changes would be required, which may negate any savings due to tolerance advantages.would be required, which may negate any savings due to tolerance advantages.



FLOATING AND FIXED FASTENERSFLOATING AND FIXED FASTENERS


Floating FastenersFloating Fasteners

When two or more parts are to be joined together using fasteners such as bolts and When two or more parts are to be joined together using fasteners such as bolts and nuts, and all of the parts have clearance holes, the relationship between the nuts, and all of the parts have clearance holes, the relationship between the fasteners and the parts being held together is called a fasteners and the parts being held together is called a ‘floating fastener’‘floating fastener’ case or case or relationship.relationship.

Where the fastener diameters are all the same size, and the clearance holes are the Where the fastener diameters are all the same size, and the clearance holes are the same for all fasteners, the formula for calculating the position tolerance is:same for all fasteners, the formula for calculating the position tolerance is:

T = h - fT = h - f

WhereWhere T = Tolerance to be applied to each partT = Tolerance to be applied to each part

h = MMC hole sizeh = MMC hole size

f = MMC fastener diameterf = MMC fastener diameter


Clearance Hole Diameter (MMC) .390Bolt Diameter (MMC) .375Position Tolerance .015

.015

Calculating Position Tolerances (Floating Fasteners)Calculating Position Tolerances (Floating Fasteners)

The value that is called out in the feature control frame is the difference between The value that is called out in the feature control frame is the difference between the MMC hole diameter and the bolt diameter at MMC.the MMC hole diameter and the bolt diameter at MMC.


T = h - fT = h - f

Features on mating parts that are to assemble, must be dimensioned on their individual Features on mating parts that are to assemble, must be dimensioned on their individual detail drawings, using the same geometric location (position) controls.detail drawings, using the same geometric location (position) controls.

Floating FastenersFloating Fasteners


Fixed FastenersFixed Fasteners

When parts are being fastened together and When parts are being fastened together and one of the parts is threaded, so that one of the parts is threaded, so that the bolt or stud is restrained,the bolt or stud is restrained, the condition is called “fixed fastener case”. the condition is called “fixed fastener case”.

If it is desirable to use the same position tolerance for each instance, and the If it is desirable to use the same position tolerance for each instance, and the fastener diameters are the same, the following formula is recommended:fastener diameters are the same, the following formula is recommended:

T = (h - f)/2T = (h - f)/2

WhereWhere T = Tolerance (applied on each feature)T = Tolerance (applied on each feature)

h = Hole size (MMC)h = Hole size (MMC)

f = Fastener size (MMC)f = Fastener size (MMC)


T = ( h - f )/2T = ( h - f )/2

This is an example of fixed fastener case. On the part that has the tapped holes, This is an example of fixed fastener case. On the part that has the tapped holes, the position tolerance would be one-half of the difference between the MMC the position tolerance would be one-half of the difference between the MMC fastener and the MMC tapped hole. This is the value that would appear in the fastener and the MMC tapped hole. This is the value that would appear in the feature control frame for position tolerance.feature control frame for position tolerance.

Fixed FastenersFixed Fasteners


PROJECTED TOLERANCE ZONES USING PROJECTED TOLERANCE ZONES USING POSITION TOLERANCESPOSITION TOLERANCES


Projected Tolerance ZonesProjected Tolerance Zones

When threaded fasteners, or press-fit pins or studs are central to functional design When threaded fasteners, or press-fit pins or studs are central to functional design and assembly, it may be necessary to control the perpendicularity of the feature and assembly, it may be necessary to control the perpendicularity of the feature axis into the space adjacent to the feature surface.axis into the space adjacent to the feature surface.

To avoid interference that can occur because of the orientation of a fixed fastener To avoid interference that can occur because of the orientation of a fixed fastener --controlled by the inclination of the hole into which it assembles-- a projected --controlled by the inclination of the hole into which it assembles-- a projected tolerance zone is used.tolerance zone is used.


Example Number OneExample Number One

No Projected Tolerance ZoneNo Projected Tolerance Zone

Parts with holes for press-fit pins, or tapped holes for posts or studs which are Parts with holes for press-fit pins, or tapped holes for posts or studs which are located with position tolerances, but without a projected tolerance zone, may located with position tolerances, but without a projected tolerance zone, may encounter interference when assembled with mating parts.encounter interference when assembled with mating parts.


2X

Projected Tolerance ZonesProjected Tolerance Zones

This is an example of tapped holes located with true position but withoutThis is an example of tapped holes located with true position but without a a projected tolerance zoneprojected tolerance zone

.010 M

.500 13 UNC – 2B

C

D

E


2X .500 13 UNC – 2B

No Projected Tolerance ZoneNo Projected Tolerance ZoneThe thread specification and position tolerance are called out on the drawing. The thread specification and position tolerance are called out on the drawing. However, there is no projected tolerance zone, and feature control is at MMC. The However, there is no projected tolerance zone, and feature control is at MMC. The cylindrical tolerance is .010 inches in diameter, and extends only to the size limits of cylindrical tolerance is .010 inches in diameter, and extends only to the size limits of the part.the part.

.010 M C


2X .500 13 UNC – 2B


As indicated, the resulting tolerance zone (axis/thread pitch diameter control) ends at As indicated, the resulting tolerance zone (axis/thread pitch diameter control) ends at the extents of the limits of size of the part.the extents of the limits of size of the part.

.010 M


2X .500 13 UNC – 2B


In this situation, the feature axis In this situation, the feature axis orientation may be anywhere within orientation may be anywhere within the limits of the cylindrical tolerance the limits of the cylindrical tolerance zone. The worst possible orientation zone. The worst possible orientation in the diagonal, is shown for this in the diagonal, is shown for this example.example.

.010 M


2X .500 13 UNC – 2B


The worst case thread orientation is The worst case thread orientation is depicted in this slide. Next, we will depicted in this slide. Next, we will depict the mating part with the depict the mating part with the clearance holes at MMC and clearance holes at MMC and maximum offset in the maximum offset in the oppositeopposite direction.direction.

.010 M


2X .500 13 UNC – 2B

.010 M


With the mating part at its With the mating part at its maximum material condition—maximum material condition—the worst possible circumstance the worst possible circumstance permitted by the tolerances on the permitted by the tolerances on the part, added to the layout, we part, added to the layout, we begin to see the consequences of begin to see the consequences of not specifying the projected not specifying the projected tolerance zone.tolerance zone.



Because no projected tolerance zone Because no projected tolerance zone was specified, there is a reasonable was specified, there is a reasonable possibility that interference will possibility that interference will result when attempting to assemble result when attempting to assemble the fastener at MMC.the fastener at MMC.


Example Number TwoExample Number Two

Projected Tolerance ZoneProjected Tolerance Zone

Projected tolerance zones extend from the datum feature (surface) away from Projected tolerance zones extend from the datum feature (surface) away from the part to a minimum distance indicatedthe part to a minimum distance indicated –either in the feature control frame, or –either in the feature control frame, or as specified by dimensions on the drawing.as specified by dimensions on the drawing.


.010 M P 1.25 C D E


The Projected Tolerance Zone is a .010 inch diameter cylinder extending a The Projected Tolerance Zone is a .010 inch diameter cylinder extending a minimum of 1.25 inches from the surface indicated, when the feature is at MMC.minimum of 1.25 inches from the surface indicated, when the feature is at MMC.

2X .500 13 UNC – 2B

C


.010 M P 1.25 C D E


2X .500 13 UNC – 2B

.010 inch positional tolerance .010 inch positional tolerance zone at MMCzone at MMC



.010 M P 1.25 C D E

2X .500 13 UNC – 2B

The projected tolerance zone and the The projected tolerance zone and the threaded (tapped) hole have been threaded (tapped) hole have been adjusted to show the worst-caseadjusted to show the worst-caseorientation. orientation.

1.25 MIN




Worst case mating part simulated Worst case mating part simulated at assembly.at assembly.

.010 M P 1.25 C D E

2X .500 13 UNC – 2B




Hardware assemblyHardware assemblywithout interference.without interference.

.010 M P 1.25 C D E

2X .500 13 UNC – 2B


SPHERICAL FEATURE CONTROLSPHERICAL FEATURE CONTROL


SPHERICAL FEATURE CONTROLSPHERICAL FEATURE CONTROL

Spherical features can be located in relation to other features using position Spherical features can be located in relation to other features using position tolerancing.tolerancing.

When used, the spherical diameter symbol precedes the dimension callout, and is When used, the spherical diameter symbol precedes the dimension callout, and is also placed in the tolerance block of the feature control frame.also placed in the tolerance block of the feature control frame.


The spherical object in this illustration is controlled in its relationship to the flat The spherical object in this illustration is controlled in its relationship to the flat planar surface. planar surface.

Spherical Feature ControlSpherical Feature Control


A

B

S 48.0 - 48.5

S 0.6 A B

Datum plane A is the origin from which the spherical diameter is positioned. The Datum plane A is the origin from which the spherical diameter is positioned. The tolerance zone is a 0.6 mm sphere which must contain the center point of the tolerance zone is a 0.6 mm sphere which must contain the center point of the spherical surface regardless of any variation in size, within its size limits. The spherical surface regardless of any variation in size, within its size limits. The axis upon which it is positioned is the axis of the shaft RFS.axis upon which it is positioned is the axis of the shaft RFS.




0.6 diameter0.6 diametersphericalspherical tolerance tolerance zonezone

Datum plane ADatum plane A

Datum Axis BDatum Axis B

A

B

S 48.0 - 48.5

S 0.6 A B

Regardless of feature size, the center Regardless of feature size, the center of the spherical element must be of the spherical element must be located on true position within a located on true position within a spherical diameter of 0.6 mm, with spherical diameter of 0.6 mm, with reference to datums A and B.reference to datums A and B.



ADVANTAGES OFADVANTAGES OFPOSITION TOLERANCESPOSITION TOLERANCES


Position Tolerance AdvantagesPosition Tolerance Advantages

Cylindrical tolerance zone -- 57% increase. Cylindrical tolerance zone -- 57% increase.

Controls tolerance accumulation.Controls tolerance accumulation.

Utilizes bonus and shift tolerances.Utilizes bonus and shift tolerances.

Supports design objectives and intent.Supports design objectives and intent.

Specifications verified using “fixed” gages.Specifications verified using “fixed” gages.

Reduces production and inspection costs.Reduces production and inspection costs.

GD&T POSITION TOL

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