Reference Guide
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Geometric Dimensioning and Tolerancing
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CCTSPLV332052016
. .. ,
1
.f'{'
manual or
Contents What
is GD& T7
Machining N~cessity
1
Flowchart
of
1
Dimensional Tolerance
2
Tolerance Dimensioning
2
Deviation
5
Fits between Mating System
of
Geometric
Parts
5
7
Fits Dimensioning
and Tolerance (GD&T) System-ASME
Terms and Definitions Maximum Material
Condition
Y14.5M-1994
9 11
(MMC)
13
GD&T Rules
15
Datums
16
GD& T Symbols and Modifiers
20
;.
,--;,f'
.
II
GD&T
Geometric Dimensioning & Tolerancing What is Geometric Dimensioning
& Tolerancing?
Geometric Dimensioning EtTolerancing (GDEtT)is a symbolic language for researching, refining, and encoding the function of each feature of a part. In addition to enabling unambiguous decoding to communicate design intent to manufacturing and quality assurance, GDEtTenables scientific tolerance stack-up analysis. and is therefore in a position to absolutely guarantee the assemble ability of in-tolerance mating parts. It consists of concepts, tools, rules, and processes,which are described in various military, national and ISO standards, and are set forth in this document in abbreviated form. Y AXIS OF DATUM REFERENCE
BASIC DIMENSION
FRAME
(A,B,C)
...
X(A,B,C)
Z(A,B,C)
-
ill}--L-----4---~--+-------------~-~I~~~1~0.-2~IA~I~B®~S1 018±0.3
(C)
027±0.3
1-$-1¢0.5@IAIB®lcl 1_L'¢0'5®'A'
DATUM FEATURE
1
A
FEATURE FRAME
1
T
(B)
LEADER
EXTENSION
LINE
CONTROL
Fig 1.1: A GDftT Encoded Drawing
Machining Flowchart Let us consider the steps involved in creating a mechanical device to solve a given problem. •
The first step is conceptual development! product design (the design stage).
•
Draft !detail the plans for each part (the drawing stage)
•
Then the individual parts are machined.
•
Next we layout an assembly plan, finally the device is assembled.
========~==
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GD&T
Machining
~
(comPletion) Fig 1.2: Machining flowchart
Necessity of Dimensional Tolerance •
It is almost impossible (and sometimes uneconomical) to maintain the strict degree of accuracy due to inevitable inaccuracy of manufacturing methods.
•
Due to interchangeability!
•
It is impossible for an operator to make perfect settings. In setting up machine .., i.e. in adjusting the tool and work piece on the machine, some errors are likely to creep in.
mass production.
To accommodate this, it is normal to display measurements with a plus or minus (+/-l tolerance which allows for some margin of above errors. Usually, the dimensional tolerance is decided at the design stage and a Machinist must take care to apply the required dimensional tolerance and to ensure that discrepancies are not introduced as a result of poor workmanship of measuring techniques. The tolerance is a compromise between accuracy required for proper functioning and the ability to economically produce this accuracy.
Tolerance Dimensioning Tolerance is the total amount that a specific dimension is permitted to vary. It is the difference between the maximum and the minimum limits for the dimension. Tolerance may be specified in 3 places: •
Directly on (with) the specified dimension
•
In a genera I note
•
In title block (tolerance block)
For example a dimension given as 1.625 ± .002 means that the manufactured part may be 1.627 or 1.623, or anywhere between these limit dimensions.
CADD® CENTRE
---===========
II
GD&T Expressing Tolerance 1.00 ± .05
III
•
~:g~III 1.00 ~:g~ 1.00 ~:gg III • 1.00
III
Equal Bilateral Tolerance
II
Bilateral Tolerance
II
Unilateral Plus Tolerance Unilateral Minus Tolerance
1.05 .98
III
II
Plus Limits, 2 Lines
.98 1.05
III
II
Minus Limits, 2 Lines
1.05 - .98
III
II
Plus Limits, 1 Lines
.98 -1.05
III
II
Minus Limits, 1 Lines
Unilateral
Bilateral
Fig 1.3: Expressing i'o/erancing
Tolerance definition - Key terms Nominal Size: It is the designation used for general identification and is usually expressed in common fractions. For Ex. In the previous figure, the nominal size of both hole and shaft, which is 11/4", would be 1.25" in a decimal system of dimensioning. Basic Size or Basic dimension: It is the theoretical size from which limits of size are derived by the application of allowances and tolerances. Actual Size: is the measured size of the finished part. Limits: The two extreme permissible sizes between which the actual size lines are called limits. Max Limit: It is defined as the maximum permissible size for a given basic size. In fig. the max limit for the basic size of Dia30 is = Dia30 + 0.035 = Dia30.035mm. Min Limit: It is defined as the minimum permissible size for a given basic size. In fig. the min limit for the basic size of Dia30 is = Dia30 - 0.215 = Dia29.785mm. Tolerance: It is defined as the amount of variation permitted to a basic size. The difference between the max and min limits of a basic size are called tolerance. In fig. the tolerance is = Dia30.035 - Dia29.785 = 0.2Smm. --=--====--=--=--====
CADD®
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a
GD&T
Deviation: is the difference between the basic size and the hole or shaft size. Upper Deviation: is the difference between the basic size and the permitted maximum size of the part. Lower Deviation: is the difference between the basic size and the minimum permitted size of the part. Actual Deviation: size.
It is the algebraic difference b/w the actual measured size and the corresponding basic
Zero Line: Since the deviations are measured from the basic size, to indicate the deviations graphically, the basic shaft, the min shaft, the actual shaft and the max shaft are aligned at the bottom and a straight line, called zero line is drawn through the top generator of the basic shaft as shown in fig. This is called zero Line because the deviations at the basic size will be zero. When the zero line is drawn horizontally, deviations above this line will be positive and below it will be negative. Tolerance zone: The zone bounded by the upper and lower limits of the basic size. Fundamental Deviation: It is that one of the two deviations which is conventionally chosen to define the position of the tolerance zone in relation to the zero line. Grades of tolerance: In a standardized system of limits and fits, group of tolerance are considered as corresponding to the same level of accuracy for all basic sizes.
~-- Basic Zero Line --
Shaft
.......
~-- Basic Hole International tolerance grade
Fundamental deviation
cl- ..
Min. size ------t~1
Max. size ---.-' Fig 1.4: Tolerance definition
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-
===========
II
GD&T Deviation It is defined as the algebraic difference between a size 8: corresponding basic size.
ZERO LINE
Deviation
SHAFT
Diameter (upper limit)
(lower limit)
Basic Size
-cei»
Fig 1.5: Deviation
Upper deviation: It is the difference of dimension between the maximum possible size of the component and its basic size. i.e. it is designated by ESfor hole 8: es for the shaft. It is a positive quantity when the maximum limit of size is greater than the basic size and negative quantity when the maximum limit of size is less than basic size. Lower deviation: Similarly, it is the difference of dimension between the minimum possible size of the component and its nominal size. i.e, It is designated by EI for hole 8: ei for the shaft. It is a positive quantity when the minimum limit of size is greater than the basic size and negative quantity when the minimum limit of size is less tha n basic size. Fundamental deviation: It defines the location of the tolerance zone with respect to the nominal size. For that matter, either of the deviations may be considered. Minimum Clearance: in a clearance fit, it refers to the difference between minimum size of the hole 8: the maximum size of the shaft. Maximum Clearance: in a clearance I transition fit, it refers to the difference between maximum size of the hole 8: the minimum size of the shaft. Minimum Interference: in a Interference fit, it refers to the difference between maximum size of the hole 8: the minimum size of the shaft. Maximum Interference: in a Interference I transition fit, it refers to the difference between minimum size of the hole 8: the maximum size of the shaft.
Fits between Mating Parts Fit is the general term used to signify the range of tightness or looseness that may result from the application of a specific combination of allowances and tolerances in mating parts.
===========
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GD&T
There are three types of fits between parts:
o
Clearance Fit In clearance fit an internal member fits in an external member (as a shaft in a hole) and always leaves a space or clearance betwr _._L'_ - - - L_
Fig 1.6: Clearance fit
e
Interference
Fit
In interference fit the internal member is larger than the external member such that there is always an actual interference of material. The smallest shaft is 1.2513" and the la rgest hole is 1.2506", so that there is an actual interference of metal amounting to at least o.ooor Under maximum material conditions the interference would be 0.0019". This interference is the allowance, and in an interference fit it is always negative.
(0)
e
iNTERFERENCE
FIT
Transition Fit Transition fit result in either a clearance or interference condition. In the figure below, the smallest shaft 1.2503" will fit in the largest hole 1.2506", with 0.003" to spare. But the largest shaft, 1.2509" will have to be forced into the smallest hole, 1.2500" with an interference of metal of 0.009':
dl.2r:-td t .__ __ ~
""'1.2503
(b)
CADDO
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TRANSITION
FIT
~ .. ~
1
II
GD&T H11/c11
Loose Running:
H9/d9
Free Running: For large temperature variations, high running speeds, or heavy journal pressures.
Ha/f7
Close Running: For accurate location and moderate speeds and journal pressures.
H7/g6
Sliding: Fit not intended to run freely, but to turn and move freely, and to locate accurately.
H7/h6
Locational Clearance: Fit provides snug fit for locating stationary parts; but can be freely assembled and disassembled.
H7/k6
Locational Transition: Fit for accurate location, a compromise between clearance and interference.
H7/n6
Locational Transition: Fit for more accurate location where greater interference is permissible.
H7/p6
Locationallnterference: Fit for parts requiring rigidity and alignment with prime accuracy of location, but without special bore pressure requirements.
H7/s6
Medium Drive: Fit for ordinary steel parts or shrink fits on light sections, the tightest fit usable with cast iron.
H7/u6
For wide commercial tolerances on external members.
Force: Fit suitable for parts which can be highly stressed or for shrink fits where the heavy pressing forces required are impractical.
System of Fits Two types of systems used to obtain various types of fits:
e
Hole Basis System In this system the different types of fits are obtained by associating shafts of varying limit dimensions with a single hole, whose lower deviation is zero. When the lower deviation of the hole is zero, the minimum limit of the hole is equal to its basic size, which is taken as the base for computing all other limit dimensions.
j_ ¢.498_c=:2_ .495~-
¢.500 .502
-r-
(0)
BASIC
HOLE.
FIT
Fig 1.9: Hole Basis System
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•
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.f
.(~ ,.(
II
GD&T
In the above figure
o
•
The minimum size of the hole 0.500" is taken as the basic size.
•
An allowance of 0.002" is decided on and subtracted from the basic hole size, making the maximum shaft as 0.498"
•
Tolerances of 0.002" and 0.003" respectively are applied to the hole and shaft to obtain the maximum hole of 0.502" and the minimum shaft of 0.495':
Shaft Basis System In this system the different types of fits are obtained by associating holes of varying limit dimensions with a single shaft, whose upper deviation is zero. When the upper deviation of the shaft is zero, the maximum limit of the shaft is equal to its basic size, which is taken as the base for computing all other limit dimensions.
_L_/~ n(.502 )U.505
j_ n(.500~_ )U.499~
~/~
'(b)
BASIC SHAFT
FIT
Fig 1.10: Shaft Basis System
•
The maximum size of the shaft 0.500" is taken as the basic size.
•
An allowance of 0.002" is decided on and added to the basic shaft size, making the minimum hole as 0.502':
•
Tolerances of 0.003" and 0.001" respectively are applied to the hole and shaft to obtain the maximum hole of 0.505" and the minimum shaft of 0.499':
IT Grade IT Grade refers to the International Tolerance Grade of an industrial process defined in ISO286 implements 20 IT tolerance. This grade identifies what tolerances a given process can produce for a given dimension. Field of use of individual tolerances of the system ISO: ITOl to IT6 - For production of gauges and measuring instruments IT5 to IT12 - For fits in precision and general engineering ITll to 1T16- For production of semi-products 1T16to IT18 - For structures ITll to 1T18- For specification of limit deviations of non-tolerated dimensions
CADD~ ~====~====~= CENTRE
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GD&T IT Grade
Fig 1.11: Machining
process associated
witt) tolerance
grades
Geometric Dimensioning and Tolerance (GD&T)System-ASME Y14.5M-1994 GD&T is an international language that is used on engineering drawings to accurately describe a part. With this the designer can properly apply geometric tolerance, they must carefully consider the fit and function of each feature of any part. This language consists of well defined set of symbols, rules, definition & conventions. GD&T encourage a dimensional philosophy called "FUNCTIONAL DIMENSIONING": functional dimensioning that defines a part based on how it functions in the final product. Consider the following example: Consider a table. Given table Height, we assume all 4 legs will be cut to length the same time.
Ii
I
20±1
_j Fig 1.12: Tuble with dimensions
===========
applied
CADD®
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m
GD&T Datum axis
Datum paints
measurement
Datum planes Origino( measurement
Fig 7.17: Datums
Some common datum feature simulators are surface plates, angle plates, chucks, mandrels, and machine tables. Feature Control Frame: Imagine the control of dimensions of this part shown here. The size and the location of the feature (cylindrical hole) is specified with basic dimension. We can now add an allowed deviation also to the feature
1--1.000--
00.500±0.010
1--1.000--
00.500±0.010
Fig 1.18: Part with dimensions
Here the tolerance must be shown as applying to the feature being controlled. Like this each controlled feature (hole, shaft, slot, surface, etc) associated with the basic dimension is given a feature control frame to show a tolerance. The tolerance that appears in the feature control frame is the allowed deviation from the perfect size or location shown by dimensions. Feature control frame has the following: A geometric characteristic symbol A tolerance zone descriptor A tolerance of location A material condition symbol Primary, secondary, and tertiary datums For our example, the component, shown with details of feature control frame would appear like this.
CADD® CENTRE
===========
m
GD&T
1-$-1 ¢O.030@ I A I B lei
Fig 1.19: Feature control
frame
Material Condition: To overcome shortcomings in symbols, modifiers can be added to change their meanings. They can be either Maximum material condition or least material condition. -..........____ Maximum Material Condition is the condition in which a feature of size contains the maximum amount of material everywhere within the stated limits of size. This means that the tolerance is at the extreme that would result if too little material was cut off, and the maximum material remains.
MMCSymbol Least Material Condition is the condition in which a feature of size contains the least amount of material everywhere within the stated limits of size. This means that the tolerance is at the extreme that would result if too much material was cut off, and the minimum material remains.
LMC Symbol
Maximum Material Condition (MMC) MMC is that condition of a part or feature which contains the maximum amount of material, e.g. minimum size hole, or a maximum size shaft The maximum material principle takes into account the mutual dependence of tolerances of size, form, orientation and/or location and permits additional tolerance as the considered feature departs from its maximum material condkion. Assembly clearance is increased if the actual sizes of the mating features are finished away from their MMC, and if any errors of form or position are less than that called for by any geometrical control.
~ ~
===~~======
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III
GD&T
Its application is restricted to those features whose size is specified by tolerance dimensions incorporating an axis or median plane. It can never be applied to a plane, surface, or line on a surface. The characteristics to which the maximum material condition concept cannot be applied are as follows: flatness, roundness, cylindricity, profile of a line, profile of a surface, run-out.
VL tc~I"'o
dition
A constant boundary generated by the collective effects of a size features specified MMC/LMC 8: the geometric tolerance for that material condition. Or
Constant value outer locus 8: constant value inner locus values are derived
o 0.1 Positional
zone atMMC
030.1 MMC size of feature - 0 0.1 Positional zone at MMC 030 Virtual condition (Inner boundary)
VIRTUAL CONDITION BOUNDARY
Pin in Plate 1
Boundary Hole in Plate 2
Virtual condition for hole >= Virtual condition for pin Fig 7.20: virtuot condition
~
•.
".tf
1
The M M C modifier applied to the position tolerance implies, that a virtual condition is defined for the features and the calculations are done with the M M C limit of size.
GD&T
o
Virtual Condition for external feature
.' . ..••
Q
O~
Virtual Condition: Pin MMC Pin
~
0 26.5
26.9 milleters
+ 0 0.4
'"
o
Pin Virtual Condition
o
The virtual condition of the pin shown here Is thus an envelop of diameter
26.9
Virtual Condition for internal feature
Virtual Condition: Hole MMC Hole '" --...;_----Condition Hole Virtual
'+~-""!
-
0 29.5
This Is an Imaginary
0
0.4
0
29.1
envelope in space and will maintain the hole boundary outside Itself
GD&T Rules ul- W· Individual Feature of Size/Perfect form at MMC/Envelope rule: Where only a tolerance of size is specified, the limits of size of an Individual future prescribe the extent to which variation in its geometric form as well as sizes are allowed. ~
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I r0.~ l.003
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MANUfACTURED
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l.OO1 t l.001
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SIZE
OUT-Of·STRAIGHTNESS
MANUFACTURED SIZE OUT OF ROUNDNESS
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GD&T
06±O.O.': FULL FORM CHECK AT 0 5.95 (MMC)
TWO POINT CHECKS AT 0 6.05 (LMC)
2X 010±O.1 Fig 1.21: GDEtT Rule I
Rule #2 RFSapplies, with respect to the individual tolerance, datum reference, or both, where no modifying symbol is specified. MMC/LMC must be specified on the drawing where it is required.
.-----------,1 PRODUCED SIZE
Symbol for RFS(past practice from Y14.5M - 1982)
1.002 1.001 1.000 .999 .998
~ 1.00:± .002
TOLERANCE
RFS
(lOmm)
.002 .002 .002 .002 .002
Fig 1.22: GOaT Rule2
Datums Datum are theoretical. It consists of:
•
Axes
•
Planes
These elements exist within a frame work of three mutually perpendicular intersecting planes known as datum reference frames. The datum reference frame is a virtual reference frame that does not exist on the part actually. Therefore it is necessaryto establish a method of simulating the theoretical reference frame from the actual features of the part.
CADD®
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-=--=-=--===-=---=--===
III
GD&T Datum Reference
Frame
y
r-------------
II
I
I
/ /
/ ~ I "v
I
I
I I I
.-----------~ I
I
/
I
xz
Z
y
/
I
~~/-
X
I
I
: I
XY
I I I
/
I I
I I
I
I
I
----------_/
Fig 1.23: Datums
,..0
1 l.f'ltior
Met-}
od
The simulation is accomplished by positioning specifically identified features in contact with appropriate datum simulators, in a stated order of precedence, to restrict motion of the datum reference frame. These specifically identified features are called as datum features.
y Datum axis
Datum
'1 Datum planes origin of measurement
Fig 1.24: Datum Simulation
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GD&T A free floating part has six degrees of freedom: • •
Rotation about X 'Rotation
about Y
•
Rotation about Z
•
Translation about X
•
Translation about Y
•
Translation about Z y
/ ®
,,~~~-+-+--CD+-~-
r® /-
~G)
z
Fig /,25: DOF
Let us the part in a simulated datum reference frame, Establishing a primary datum reference frame, we see two rotational and one linear degree of freedom are eliminated, Now bringing in a secondary datum plane we find that more degreesof freedom are eliminated. Now bringing the part in contact with a tertiary datum plane, the remaining single degree of freedom is also eliminated and this provides a positive part orientation for any manufacturing or inspection procedure required. y
"
Fig 1.26: Dotum Simutation
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--------
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GD&T--------------------------------------a tu
1
II
L'ea~ure
Consider a surface plate having a real feature of adequately precise form contacting the datum features. This real surface is called as simulated datum features. Now consider a part, a real feature of a part (in this case a surface). which is used to establish the location of a datum is called as datum feature. As datum features are subject to manufacturing errors and variations, it may be necessary, where appropriate to specify tolerances of form to them.
Simulated Datum Feature
..
Surface Plate
Fig 1.27: Datum Feature
Datum Targets Datum targets are specific portions of a surface, line or point that may be used for datum referencing. Sometimes due to the configuration of a part, its function in assembly or its rough or warped surfaces, it becomes desirable to use only a portion of the surface as a datum. The portion may be designated as a point or points, a line or lines, or an area or areas.The areas may be defined as any shape that is appropriate.
i
Fig 1.28: Datum Targets
GD&T Datum Target symbols Points, lines and areas on datum features are designated on the drawing by means of a datum target symbol. The datum target symbol consists of a circle cut in to two halves. The top tier contains the target area size that can be placed either internally or externally as shown. The lower tier contains a datum identifying letter with a target number.
@
010 Al
-'lr----r.__--,/
®
Fig 1.29: Datum Target Symbols
The symbol is placed outside the part outline with a radical (leader) line directed to the target. The use of solid radial line indicates that the datum target is on the rear surface. The use of a dashed radial line indicates that the datum target is on the far (hidden) surface.
GD&T Symbols and Modifiers ASME follows fourteen geometric symbols and the modifiers as given in the table. TYPE OF
FEATURES
TYPE OF TOLERANCE
CHARACTERISTICS FLATNESS
INDIVIDUAL (NO Datum Reference)
STRAIGTNESS
LINE PROFILE
0 1:/ r-.
SURFACE PROFILE
0
PERPENDICULARIT
...L
ANGULARITY
L
PARALLELISM
II
CIRCULAR RUNOUT
;t
CIRCULARITY
PROFILE
ORIENTATION
RELATED FEATURES (Datum Reference Required)
0
FORM
CYLINDRICITY INDIVIDUAL or RELATED FEATURES
SYMBOL
RUNOUT TOTAL RUNOUT CONCENTRICITY LOCATION
.!!J1 0 --
POSITION
~
SYMMETRY
-
Fig 1.30: Geometric Symbols
r
GD&T
Ell TERM AT MAXIMUM
MATERIAL
AT LEA8T MATERIAL PROJECTED
SYMBOL CONDITION
TOLERANCE
ZONE
FREE STATE TANOENT
DIAMETER
¢ s¢
RADIUS
R SR
DIAMETER
RADIUS SPHeRICAL CONTROLLED
CR
RADIUS
REFERENCE
()
ARC L£NOTH
.........
STATISTICAL
Modifying symbols
(f)
PLANE
SPHERICAL
@
© ® ®
CONDInON
Additional Symbols
(ill +-+
TOLERANCE
BETWEEN
Fig 1.31: Modifiers
Profile tolerances
o
Profile of a Line
A uniform two dimensional zone limited by two parallel zone lines extending along the length of a feature. The amount of deviation that is allowed for a surface to float within a certain dimensional range while maintaining the shape or form of each line elements that makes up that surface.
Fig 1.32: Profile of a line
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GD&T
Profile of a Surface
It is the amount of deviation that is allowed for a surface.
Fig 1.33: Profile of a surface
A uniform three dimensional zone contained between two envelope surfaces separated by the tolerance zone across the entire length of a surface.
Orientation tolerances
o
Angularity
L The distance between two parallel planes, inclined at a specified basic angle in which the surface, axis, or center plane of the feature must lie. It requires that all points on a specified feature must form an angle with a datum.
Fig 1.34: Angularity
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l ft" ,,/' ..fro
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GD&T ----------------------------------------
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Perpendicularity
j_ The condition of a surface, axis, median plane, or line which is exactly at 90 degrees with respect to a datum plane or axis. It requires that all points on a specified feature must be perpendicular with a datum. ~
~I.-------.
~ ~ ~ ~ ~ ~
/. : ~.u.,""" .. """""""/.""'/..,...J/.!-,/ /.,..-,/.....,./.....,-/....,.../..,..../..,.-/ /."""/."""/."""/"'""' 0.003 Tolerance Zone Fig 1.35: Perpendicularity
o
Parallelism
II The condition of a surface or axis which is equidistant at all points from a datum of reference. All points on a surface are to be parallel to a given datum, within a specified tolerance.
_[0.01
1 1.. Fig 1.36: Parallelism
Tolerance Zone
II
GD&T
Locational
o
Tru
tolerances
Position
A zone within which the center, axis, or center plane of a feature of size is permitted to vary from its true (theoretically exact) position. A position tolerance generates a tolerance zone that confines the center, center plane or axis of a feature of size. It is also capable of confining a surface or surfaces within or outside of a boundary known as virtual condition.
1-$-1 ¢o.o30@1
1 1c 1
0 B
1.500
4X00.2000±0.010 Fig 1.37: True position
o
Concentricity
A cylindrical tolerance zone whose .axis coincides with the datum axis and within which all crosssectional axes of the feature being controlled must lie. (Note: Concentricity is very expensive and timeconsuming to measure. Concentricity is a geometric control of the median points of all diametricallvopposed elements of a figure of revolution.
A Fig 1.38: Concentricity
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Symmetry
Symmetry is that condition where the median points of all opposed or correspondingly located elements of two or more feature surfaces are congruent with the axis or center plane of datum feature.
1-=-1.0051 ciA 1
..
..r
1.000±.005
1..--------+- 1 --
1.375±.001
.875±.005
.___,J 1-1
..
---
2.000±.005 --
...... -11
__j
.700±.001
L
Fig 1.39: Symmetry
Runout tolerances
o
Circular Runout
A composite tolerance used to control the relationship of one or more features of a part to a datum axis during a full 360 degree rotation about the datum axis.
0.02
Tolerance Zone
[ Fig 1.40: Circular runout
----------
-
-
GD&T
o
Total Runout
All surface elements across the entire surface of the part must be within the runout tolerance.
Tolerance Zone
Fig 1.41: Total runout
Form tolerances
o
Flatness
o A two dimensional tolerance zone defined by two parallel planes within which the entire surface must lie. Basically all the surface elements are constrained to lie within two parallel planes, separated by the tolera nee.
1010.0011
r
Tolerancezo: ~:~
_
'--------'==r:f
t
Fig 1.42: Hotness
o
Straightness A condition where an element of a surface or an axis is a straight line. One of the surface elements is constrained to lie within two parallel surface planes separated by the tolerance. This means that if any line across the surface is within two parallel lines, the part is acceptable.
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.' .t s .I:"
GD&T
iii 1-10.0011
I
Tolerance Zone 0.001
L_
_
Fig 1.43: Straightness
o
Circularity
o A condition on a surface of revolution (cylinder, cone, sphere) where all points of the surface intersected by any plane perpendicular to a common axis (cylinder, cone) or passing through a common center (sphere) are equidistant from the axis of the center. All of the points on a cylindrical surface are constrained to lie within two circles. It is a 2-D surface form control.
-------$
0.01 Tolerance Zone
Fig 1.44: Circularity
o
Cylindricity
A condition on a surface of revolution in which all points of the surface are equidistant from a common axis. It is an extension to circularity that specifies the tolerance along the cylinder. It is a 3-D form control which controls roundness (circularity), straightness and taper.
L' 1:11
0.0011
-+-- ----~- $ 0.001 Tolerance Zone Fig 1.45: Cylindricily
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GD&T
Index A Actual Deviation 4 Actual Size 3 Angularity 22
B Basic Size or Basic dimension 3
C Circularity 27 Circular Runout 25 Clearance Fit 6 Concentricity 24 Cylindricity 27
o Datum Feature 19 Datums 11 Datum Targets 19 Datum Target symbols 20 Deviation 4
E
IT5 to ITl2 8 IT11 to ITl6 8 ITl 1 to ITl 8 8 IT16 to ITl 8 8 IT Grade 8
L LeastMaterial Condition 13 Limits 3 Locational tolerances 24 Lower deviation 5 Lower Deviation 4
M Machining Flowchart 1 Material Condition 13 Maximum Clearance 5 Maximum Interference 5 Maximum Material Condition 13 Maximum Material Condition (MMC) Max Limit 3 Minimum Cledrance 5 Minimum Interference 5 Min Limit 3
13
Expressing Tolerance 3
N
F Feature 11 Feature of Size 1 1 Fits between Mating Parts 5 Flatness 26 Form tolerances 26 Fundamental deviation 5 Fundamental Deviation 4
G GD& T Rules 15 GD&T Symbols and Modifiers 20 Grades of tolerance 4
Necessity of Dimensional Tolerance 2 Nominal Size 3
o Orientation tolerances 22
p Parallelism 23 Perpendicularity 23 Profile of a Line 21 Profile of a Surface 22 Profile tolerances 21
R
H Hole Basis System 7
Rule # 1 15 Rule #2 16 Runouttolerances 25
Interference Fit 6 ITO1 to IT6 8
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II S Shaft Basis System 8 Simulation Method 17 Straightness 26 Symmetry 25 System of Fits 7
T Termsand Definitions 1 1 Tolerance 3 Tolerance definition - Key terms 3 Tolerance Dimensioning 2 Tolerance zone 4 Total Runout 26 Transition Fit 6 True Position 24
U Upper deviation 5 Upper Deviation 4
V Virtual Condition 14 Virtual Condition for external feature 15 Virtual Condition for internal feature 15
Z Zero Line 4
II
GD&T
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