Geometric Geometric Dimensioning Dimensioning and an ddTToler ol eran ancin cing gg (GD& (G D&T TT)) and an oler ol eran ancin cing (GD& (G D&T
MANAGEMENT
S R O D N E V
S R E M O T S U C
DESIGN SALES
PRICING TOOLING TOOLIN G PLANNING
PURCHASING PRODUCTION
ROUTING
SERVICE INSPECTION
ASSEMBLY
PART PRODUCTION COMMUNICATION MODEL
Thr Th rreeee C Thr Th Caatteeggoorriieess oof f Dimensioning Dimensioning Dimensioning can be divided into three categories: •general dimensioning, •geometric dimensioning, and •surface texture. The The following provides information necessary to begin to understand geometric dimensioning and tolerancing (GD&T)
LLimit im ititTToler ol eran ancin cing ggA lie dd imit im oler ol eran ancin cing Apppplied lied lie To Ang Blo To A Ann An Anggllee Bl Bloocckk
Geometric Geometric Tolerancing Tolerancing Applied Applied To To An An Angle Angle Block Block
Geometric Geometric Dimensioning Dimensioning & & Tol To GD & Tollleerraanncciinngg((GD& To GD& GD &T) T)
GD&T is a means of dimensioning & tolerancing a drawing which considers the function of the part and part rt functio f unctions ns how this pa w ith rela relate ted d pa p arts rt s . – This allow allows a dr drawin awing g to contain a more defined feature more accurately, without increasing tolerances.
GD&T GD&T cont’d cont’d
GD&T has increased in practice in last 15 years because of ISO 9000. – ISO IS O 9000 9000 requ requir ires es not only that hat somet somethi hing ng be required, but how it is to be controlled. For example, how round does a round feature have to be?
GD&T is a system that uses standard symbols to indicate tolerances that are based on the feature’s geometry. – S omet ometim imes es called feat featur ure e based based dimensioning & tolerancing or true position dimensioning & tolerancing
GD&T practices are specified in ANSI Y14.5M-1994.
For For Example Example
Given Table Height Assume all 4 legs will be cut to length at the same time.
However, all surfaces have a degree of waviness, or smoothness. For example, the surface of a 2 x 4 is much wavier (rough) than the surface of a piece of glass. – As the table heigh heightt is dimen dimensioned sioned,, the the following table would pass inspection.
or
If top top mus mustt be flatter, flatter, you could could tighten the tolerance to ± 1/32. – Howev However, now now the heigh heightt is restri restrict cted ed to to 26.97 to 27.03 meaning good tables would be rejected.
Example Example cont’d. cont’d. Yo Y ou can have both, by usi sin ng GD&T.
– The table table heigh heightt may any height height between 26 and 28 inches. – The table table top top must must be flat wit ithin hin 1/16. (±1/32)
.06
.06
.06
26
27
28
W GD& IMP TANT WHY HY IS IS GD&T GD& GD &TT IMPOR IMPORTANT IMPOR ORTANT TANT
Saves money – For ex example ample,, if large large num numbe berr of parts are being made – GD&T can reduce or eliminate inspection of some features. – P rovid ovides es “b “bonu onus” toler olerance ance Ensures design, dimension, and tolerance requirements as they relate to the actual function Ensures interchangeability of mating parts at the assembly P rovides rovides uniformit uniformity y It is a universal understanding of the symbols instead of words
WHE WH EEN US GD& TT WHE WH N TO TO USE USEE GD&T USE GD&T GD&
When part features are critical to a function or interchangeability When functional gaging is desirable When datum references are desirable to insure consistency between design When standard interpretation or tolerance is not already implied When it allows a better choice of machining processes to be made for production of a part
TERMIN TE RMINOLOGY OLOGY RE EW TERMIN TE RMINOLOGY OLOGY REVI REVIEW REVI VIEW EW Maximum xi mum Mate teri ria al Cond onditi ition on (MMC): The The condition where a si size ze feature contains the maximum amount of material within the stated limits of size. I.e., largest shaft and smallest hole. Lea Least st Ma Material terial Con ondi diti tion on (LMC) LMC): The The condition where a size feature contains the least amount of material within the stated limits of size. I.e., smallest shaft and largest hole. Tolerance: Difference between MMC and LMC limits of a single dimension. A All l o w an anc c e: Difference between the MMC of two mating parts. (Minimum clearance and maximum interference) Ba Basic sic Dim ime ension: nsi on: Nominal dimension from which tolerances are derived.
LIMITS LIM ITS IZ EE LIMITS LIM ITS OF OF SSIZE IZE IZ
SIZE DIMENS DIMENSION ION
WHAT DOE DOES S THIS MEAN? MEAN? 2.007 2.003
LIMITS LIM ITS IZ EE LIMITS LIM ITS OF OF SSIZE IZE IZ A variation in form is allowed between the least material condition (LMC) and the maximum material condition (MMC). SIZE DIMENSION ENVELOPE PRINCIPLE MMC MMC (2.007)
LMC (2.003)
ENVELOPE ENVELOP E OF SIZE SIZE
Envelop nvelop Principle defines the size and form relationships between mating parts.
LIMITS LIM ITS IZ EE LIMITS LIM ITS OF OF SSIZE IZE IZ
ENVELOPE PRINCIPLE
LMC CLEARANCE
MMC MMC ALLOWANCE
LIMITS LIM ITS IZ EE LIMITS LIM ITS OF OF SSIZE IZE IZ The The actual si size ze of the feature at any cross section must be within the size boundary. ØMMC ØLMC
LIMITS LIM ITS IZ EE LIMITS LIM ITS OF OF SSIZE IZE IZ No portion of the feature may be outside a perfect form barrier at maximum material condition (MMC).
Other OtherFactors Factors
II.e., PPar allel llLin LLin eeTole TTole rrance an ce Zo .e.,Par Paralle aralle allel Line ine Toler oler ance an ceZon Zonnes Zon es
P ARALLE L LINES
P AR ALLE L LINES
P ARALLE L LINE S
P ARALLEL P LANES
P AR ALLE L P LANE S
PARALLEL PLANES
P AR ALLE L P LANE S
P AR ALLEL P LANES
CY LINDE R ZONE
GEOMETRIC GEOMETRIC CHARACTERISTIC CHA RACTERISTIC CONTROLS 14 characterist ics th at may be cont rol led
TYPE OF FEATURE
TYPE OF CHARAC HARACT TERIS ERIST TIC SY SYMBO MBOL L TOLERANCE FLATNESS
INDIVIDUAL (No Datum Reference)
STRAIGHTNESS FORM CIRCULARITY CYLINDRICITY
INDIVIDUAL or RELATED RE LATED FEATURES
LINE LINE P ROFILE PROFILE SURFACE PROFILE PERPENDICULARITY ORIENTATION ANGULARITY PARALLELISM
RELATED FEATURES (Datum Reference Required)
CIRCULAR RUNO R UNOUT UT RUNOUT TOTAL RUNOUT CONCENTRICITY LOCATION
POSITION SYMMETRY
Characteristics Characteristics& &Symbols Symbols cont’d. cont’d.
– – – – –
Maxim Maximum um Mater Material ial Con Condi dittion MMC Regardless of F eature Si Size RF S Least east Mater Materia iall Con Cond dit itiion LMC P rojec ojectted Toler oleran ance ce Zone one Diamet Diametrrical (Cy (Cylindr lindrical) ical) Toleran olerance ce Zone or Feature – Basic, or or E xact act, Dim Dimension – Datu Datum F eat eature Sy S ymbol – F eat eature Cont ontrol F rame
Feature Control Frame FEATURE CONTROL CONTROL FRAME Feature Control Frame GEOMETRIC GEOMET RIC SYMBOL SYMB OL TOLERANCE INFORMATION DATUM DA TUM REFERENCES REFERENCES COMPARTMENT VARIABLES
THE RELATIVE TO OF THE FEATURE MUST BE WITHIN CONNECTING WORDS
Feature Feature Control Control Frame Frame
Uses feature control frames to indicate tolerance
Read eads as: The position of the featur feature e must must be be wit ithin hin a .003 diametrical tolerance zone at maximum material condition relative to datums A, B, and C.
Feature Feature Control Control Frame Frame
Uses feature control frames to indicate tolerance
Read eads as: The position of the feature must be wit ithin hin a .003 diametrical tolerance zone at maximum material condition relative to datums A at maximum material condition and B.
Reading ReadingFeature FeatureControl ControlFrames Frames
The The zone.
of the feature must be within a
The The tolerance zone zone at to Datum Datum .
tolerance
of the feature must be within a relative relative
The The
of the feature must be within a tolerance zone zone relative to to Datum Datum .
The The
of the feature must be within a zone at relative to Datum .
The The of the feature must be within a tolerance tolerance zone zone relative to datum datums .
PPlacem lac ement ent FFeat ure ee lacem lac ement entof of Feat Featur eatur ure Control Control Frames Frames
May be attached to a side, end or corner of the symbol box to an extension line.
Applied to surface.
Applied to axis
PPlacem lac ement ent FFeat ure ee lacem lac ement entof of Feat Featur eatur ure Control Control Frames Frames Cont’d. Cont’d.
May be below or closely adjacent to the dimension or note pertaining to that feature. Ø .500± .500±.005
Basic Bas asic icDimension Dimen Dim ens sion
A theoretically exact size, profile, orientation, or location of a feature or datum target, therefore, a basic dimension is untoleranced. Most often used with position, angularity, and profile) Basic dimensions have a rectangle surrounding it.
1.000
B as ic Dim ens ssion Basic asic as ic Dimen Dimen Dim ens ion cont’d. cont’d.
Form Form Features Features
Individual Features No Datum Reference
F latness
S traightness
Circularity
Cylindricity
FForm or m eat uurres am pples orm or mFFeatu eatu eat esEExxamp amp am les Flatness as state s tated d on on drawing: The The flatness of the feature must be within .06 tolerance zone.
Straightn traigh tne ess applied appl ied to a flat surface sur face:: The The straightness of the feature must be within .003 tolerance zone. .003
0.500 ±.005
.003
0.500 0.500 ±.005
FForm or m eat uurres am pples orm or mFFeatu eatu eat esEExxamp amp am les Straightness applied to the surfa surf ace of a diameter: The The st strraightness of the feature must be within .003 tolerance zone. .003
0.500
0.505
Straightn traigh tne ess of an Axis at MMC: MMC: The The derived median line straightness of the feature must be within a diametric zone of .030 at MMC. 0.500
0.505 1.010 0.990
.030 M
Dial Dial Indicator Indicator BEZEL
2
CASE
2
4
4
6
6
8
8 10
12
10
CLAMP
PROBE
Verification Verification of of Flatness Flatness
Activity Activity 13 13
Work on worksheets GD&T 1, GD&T 2 #1 only, and GD&T GD&T 3 – (for (for GD&T D&T 3 comp completely letely dimens dimension. ion. ¼” ¼” grid.) grid.)
Features Features that that Require Require Datum Datum Reference Reference
Orientation – P erp erpendicula cularrity – An Ang gularity – P arallelism
Runout – Circ Circular Runout – Tot Total Run Runout
Location – P osition – Concen centricit city – S ymmetry
Datum Datum
Datums are features (points, axis, and planes) on the object that are used as reference surfaces from which other measurements are made. Used in designing, tooling, manufacturing, inspecting, and assembling components and subassemblies. – As you know, now, not not ever every y GD&T D&T feature requires a datum, i.e., Flat
1.000
Datums cont’d. Datums cont’d. Features are identified with respect to a datum. Always start with the letter A Do not use letters I, O, or Q May use double letters AA, BB, etc. This information is located in Thi the feat feature control frame. frame.
Datum Datums s on a draw drawing ing of a part are represented using the symbol shown below.
Datum Datum Reference Reference Symbols Symbols The The datum feature sym symbol identifies a surface or feature of size as a datum.
A
A
ASME 1994
ISO
A ANSI 1982
PPlac la ccement em ent D ums ss lac la ement em ent ooff Dat Datum Dat atum ums
Datums are generally placed on a feature, a centerline, or a plane depending on how dimensions need to be referenced. A
OR
A
ANSI 1982 ASME 1994
Line up with arrow only when the feature is a feature of size and is being defined as the datum
A
PPlac la ccement em ent D ums ss lac la ement em ent ooff Dat Datum Dat atum ums
Feature sizes, such as holes Ø .500± .500±.005 .005
A
Sometimes a feature has a GD&T and is also a datum A
Ø .500± .500±.005
Ø .500± .500±.005
TWE TW EELV LVE EE DE D GR EEEES S OF RE EED TWE TW LVE LV DEEGRE DE GRE GR OF FFRE FREE REE DOM OM
UP BACK
LEFT
6 LINEAR AND 6 ROTATIONAL DEGREES OF FREEDOM
RIGHT
FRONT DOWN
UNRESTRICTED FREE MOVEMENT IN SPACE
Example Example Datums Datums
Datu Datums must be perpendicular to each other – P rimary
– Secondary
– Tert ertiary iary Datu Datum
PPrimary rim ary Da tum rimary rim ary Dat Dat atum um
A primary datum is selected to provide functional relationships, accessibility, and repeatability. – F unction ctional al Relat elationship ionships s » A st standar andardizat dization ion of size is desired desired in the manufacturing of a part. » Cons onsid idera erattion of of how how part parts s are orientated to each other is very important. – F or exam exampl ple, e, legos legos are are mad made e in a standard size in order to lock into place. A primary datum is chosen to reference the location of the mating features.
– Acce Accessibi ssibility » Does anyt anything, hing, such as, sha shaft fts, s, get get in the way?
PPrimary rim ary Da tum rimary rim ary Dat Dat atum um
cont’d. cont’d.
– Repea epeattabil abilit ity y For example, castings, sheet metal, etc. » The prim primary ary datum datum chosen chosen mus mustt insure precise measurements. The The su surrface est sta ablish she ed must produce consistent » Meas Measur urem ement ents s when when producing producing many identical parts to meet requirements specified.
PPrimary rim ary at um rimary rim ary D Datum atum at um
Restricts 6 degrees of freedom
FIR ST DATUM FIRST DATUM E STABLISHED BY THREE THRE E POIN P OINTS TS (MIN) (MIN) CONTACT WITH SIMULATED DATUM A
Secondary Secondary & & Ter Te rrttiiaarryy D Ter Te Daattu um mss
All dimension may not be capable to reference from the primary datum to ensure functional relationships, accessibility, and repeatability. – S econ econd dary ary Dat Datum » Secondary econdary datum datums s are prod produced uced perpendicular to the primary datum so measurements can be referenced from them.
– Tert ertiar iary Dat Datum » This datum datum is always always perpen perpendicular dicular to both the primary and secondary datums ensuring a fixed position from three related parts.
Secondary Secondary Datum Datum
Restricts 10 degrees of freedom.
S EC ECOND OND DATUM P LAN LANE E ESTABLISH E STABLISHED ED BY TWO P OIN OINTS TS (MI (MIN) N) CONTACT WITH SIMULATED SIMULATE D DATUM B
Ter Te rrttiiaarryy D Ter Te Daattuum m
Restricts 12 degrees of freedom.
90°
MEASURING DIREC DIRECTION TIONS S FOR F OR RELATED DIMENSIONS
THIRD DATU THIRD ATUM M P LAN LANE E ESTABL E STABLISHED ISHED BY ONE P OINT (MIN (MIN)) CONTACT WITH SIMULATED DATUM C
Coordinate Coordinate Measuring Measuring Machine Machine B R I D G E D E S IG N
PROBE
Z
GRANITE SURFACE PLATE
DATUM REFERENCE FRAME
S D Siizzee Da Daattuum Da m (CIRCULAR) (CIRCULAR)
THIS ON THIS THE DRAWIN RAWING G
A
MEANS THIS
PART DATUM AXIS
SIMULATED DATUMSMALLEST CIRCUMSCRIBED CYLINDER
S D Siizzee Da Daattuum Da m (CIRCULAR) (CIRCULAR)
THIS ON THIS THE DRAWIN DRAWING G A
MEANS THIS
PART DATUM DA TUM AXIS A
SIMULATED DATUMLARGEST INSCRIBED CYLINDER
Orientation Orientation Tolerances Tolerances – P erp erpend endicula icularrit ity y – Angularit larity y – P arallelism Controls the orientation of individual features features
Datum Datums s are are requir required ed
Shape of tolerance zone: 2 parallel lines, 2 parallel planes, and cylindrical
PERPENDICULARITY: PERPENDICULARITY:
is the condition of a surface, center plane, or axis at a right angle (90°) to a datum plane or axis. Ex: Ex: The The perpendicularity of this surface must be within a .005 tolerance zone relative to datum A.
The The tolerance zon zone is the space between the 2 parallel lines. They are perpendicular to the datum plane and spaced .005 apart.
PPrractice act ice PPr ob lem m actice act icePr Prroble oble ob lem m
P lane 1 mus mustt be perpendicular within .005 tolerance zone to plane 2.
BOTTOM SURFACE SURF ACE
PPrractice act ice PPr ob lem m actice act icePr Prroble oble ob lem m
P lane 1 mus mustt be perpendicular within .005 tolerance zone to plane 2
BOTTOM PLANE
PPrractice act ice PPr ob lem m actice act icePr Prroble oble ob lem m
2.00±.01
.02 Tolerance
Without GD & T this would be acceptable
2.00±.01 .005 Tolerance Zone .02 Tolerance
With GD & T the overall height may end anywhere between the two blue planes. But the bottom plane is restricted to the red tolerance zone.
PERPENDICULARITY PERPENDICULARITY
Cont’d. Cont’d.
Location of hole (axis)
Thi This means ‘the hole (axis) must be perpendicular within a diametrical diametrical tolerance zone of .010 relative to datum A’
A ANGUL NGULA A ANGUL A NGULA ARITY: RITY:
is the condition of a surface, axis, or median plane which is at a specific angle (other than 90°) from a datum plane or axis. The The su surrface is at a 45º 45º angle angle wit with a .005 tolerance zone relative to datum A.
Can be applied to an axis at MMC. Typically must have a basic Typ dimension.
PARALLELISM: PARALLELISM:
The The condition of a su surrface or center plane equidistant at all points from a datum plane, or an axis. The The dist sta ance between the parallel lines, or surfaces, is specified by the geometric tolerance.
±0.01
Activity Activity 13 13
Cont’d. Cont’d.
Complete worksheets GD&T2, GD&T-4, and GD&T-5 – Comp ompletely letely dim dimen ens sion. ion. – ¼” grid
Material Material Conditions Conditions Maximum Material Condition (MMC) Least Material Condition (LMC) Regardless of Feature Size(RFS)
Maximum Maximum Material Material Condition Condition MMC Thi This is when part will weigh the most.
– MMC for for a shaft shaft is th the lar largest allowable size. Ø0.240±.005? » MMC of Ø0.240
– MMC for a hole ole is the smal smalle lest st allowable size. Ø0.250±.005? » MMC of Ø0.250
P ermit ermits s great greater er pos poss sible tolerance as the part feature sizes vary from their calculated MMC Ensures interchangeability Used – Wit ith h int interrelat errelated ed featur features es with with respect to location – S ize, ize, such such as, as, hol hole, e, slot slot, pin pin, etc. etc.
Least LeastMaterial MaterialCondition Condition LMC LMC This is when part will weigh Thi the least.
– LMC for for a shaf shaftt is th the smal smallest lest allowable size. Ø0.240±.005? » L MC o f Ø0.240
– LMC for a hole ole is the lar largest allowable size. Ø0.250±.005? » L MC o f Ø0.250
Regardless Regardless of of Feature Feature Size Size RFS Requires that the condition of the material NOT be considered. This is used sed when the si size ze Thi feature does not affect the specified toleran tolerance. ce. Valid only when applied to features of size, such as holes, slots, pins, etc., with an axis or center plane.
Location Location Tolerances Tolerances
– P osi sittion – Concen oncenttricity icity – S ymmetr etry
Position Position Tolerance Tolerance A position tolerance is the total permissible variation in the location of a feature about its exact true position. For cylindrical features, the position tolerance zone is typically a cylinder within which the axis of the feature must lie. For other features, the center plane of the feature must fit in the space between two parallel planes. The exact posi sittion of the feature is The located with basic dimensions. The posi sittion tolerance is typically The associated with the size tolerance of the feature. Datums s are are requ require ired d. Datum
Coordinate Coordinate System System Position Position
Consider the following hole dimensioned with coordinate dimensions:
The The tolerance zon zone for the location of the hole is as follows:
2.000
0 5 7 .
Several Problems: – Two points, points, equidistan equidistantt from from true rue position position may may not be accepted. – Total toler toleran ance ce diag diagon onally ally is .014, .014, which which may be more than was intended.
Coordinate Coordinate System System Position Position
Consider the following hole dimensioned with coordinate dimensions:
The The tolerance zon zone for the location (axis) of the hole is as follows: Center can be anywhere along the diagonal line. 2.000
0 5 7 .
Several Problems: – Two points, points, equidistan equidistantt from from true rue position position may may not be accepted. – Total toler toleran ance ce diag diagon onally ally is .014, .014, which which may be more than was intended. (1.4 Xs >, 1.4*.010=.014)
Position Position Tolerancing Tolerancing
Consider the same hole, but add GD&T:
Now, overall tolerance zone is:
MMC = .500 .5 00 - .0 .003 03 = .49 .497 7
The The actual center of the hole (axis) must lie in the round tolerance zone. The same tolerance is applied, regardless of the direction.
Bonus Bonus Tolerance Tolerance
Here is the beauty of the system! The specified tolerance was:
Thi This means that the tolerance is .010 i f the hole size is the MMC size, or .497. If the hole is bigger, we get a bonus tolerance equal to the difference between the MMC size and the actual size.
Bonus Bonus Tolerance Tolerance Example Example Thi This means that the tolerance is .010 i f the hole size is the MMC size, or .497. If the hole is bigger, we get a bonus tolerance equal to the the difference difference between the MMC size and the actual size.
.503
Actual Actual Hole Size Siz e
Bonus Tol.
Φ
Ø .497 .497 (MMC) (MMC)
0
.010
Ø .49 .499
.002
(.010 + .002 =.012)
.012
Ø .50 .500 (.500 - .497 =.003)
.003
(.010 + .003 =.013) .013)
.013
Ø .50 .502
.005
.015
Ø .503 .503 (LMC)
.006
.016
Ø .50 .504
?
?
(.499 - .497 =.002)
of Tol. Zone
Thi This syst syste em makes sen sense… se… the larger the hole is, the more it can deviate from true position and still fit in the mating condition!
Hole
.497 .497 =BON ONU US 0 TOL TOL ZO ZONE .010
Shaft
.499 - .49 .497 =BON ONU US .002 BON ONU US +TOL OL.. ZONE ZONE =.01 .012
.501 - .49 .497 =BON ONU US .004 .004 BON ONU US +TOL OL.. ZONE ZONE =.01 .014
.503 - .497 =BON ONU US .006 BON ONU US +TOL OL.. ZONE ZONE =.01 .016
What if the tolerance had been specified as:
Since there is NO material modifier, the tolerance is RFS, which stands for regardless of feature size. This means that the position tolerance is .010 at all times. There is no bonus tolerance associated with this specification.
VIRTUAL VIRTUAL CONDITION CONDITION: The worst case boundary generated by the collective effects of a size feature’s specified MMC or LMC material condition and the specified geometric tolerance.
GT =GEOMETRIC TOLERANCE TOLERANCE
PERPENDICULARITY PERPENDICULARITY
Cont’d. Cont’d.
Means “the hole (AXIS) must be perpendicular within a diametrical tolerance zone of .010 at MMC relative to datum A.” A. ”
Actual Hole Size 1.997 1.997 (MMC) (MMC) 1.998 1.999 2.000 2.001 Vc =
2.002 2.003
Bonus Tol Tol.
Ø of Tol Tol. Zone
Activity Activity 13 13
Cont’d. Cont’d.
Worksheet GD&T 6
