04 Form Tolerances

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Interpret the f latness contro l .
Interpret the straigh tness con trol .
Interpret the circular ity con trol .
Interpret the cyl ind r ic i ty contro l .
FORM CONTROLS
Flatness
Straightness
Circularity
Cylindricity

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FLATNESS
ZONE OF TOLERANCE : TWO PARALLEL PLANES
SYMBOL :
STRAIGHTNESS
ZONE OF TOLERANCE : CYLINDER
SYMBOL :

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CIRCULARITY
ZONE OF TOLERANCE : TWO COPLANAR CONCENTRIC CIRCLES
SYMBOL :
CYLINDRICITY
ZONE OF TOLERANCE : TWO COAXIAL CYLINDERS
SYMBOL :
t=0.3
t=0.3
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Definition : Flatnessis the condition of a surface having all of itselements in one plane. The tolerance zone for aflatness control is threedimensional.
General representation
FLATNESS
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Interpretation of Flatness tolerance :
It consists of two parallel planes within whichall the surface elements must lie. The distancebetween the parallel planes is equal to theflatness control tolerance value.
FLATNESS
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Rule #1 Effect on Flatness
Whenever Rule #1 applies to a feature of size that consists of twoparallel planes, an automatic indirect flatness control exists for bothsurfaces.
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Rule #1 Effect on Flatness
When the feature of size is at MMC, both surfaces must be perfectlyflat.
As the feature departs from MMC, a flatness error equal to the amountof the departure is allowed.
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Flatness Control Application
Some examples of when a designer uses flatness
control on a drawing are to provide a flat surface: For a gasket or seal.
To attach a mating part.
For better contact with a datum plane.
When these types of applications are involved, the
indirect flatness control that results from Rule #1
is often not sufficient to satisfy the functional
requirements of the part surface.
This is when a flatness control is specified on a
drawing
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Each two point
measurement must
be within the
dimensional limits
The size requirement
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Rule #1 boundary requirement
The part mustbe within a 10.6
boundary
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The Flatness requirement
All of the surfaceelements must be
within two parallel
planes 0.2 apart
Two parallel
plane 0.2
apart
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STRAIGHTNESSDefinition :
Straightness of a line elementis the
condition where each line element (or axis or centerplane) is a straight line.
The tolerance zone for a straightness control(as a surface line element control is twodimensional).
General Representation :
0.05
10.6
10.4
1. When applied to a surface
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2. When applied to an axis
3. When applied to a center plane
10.610.4
0.1
10.610.4
0.1
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Interpretation (Straightness applied to the surface element)
The straightness controldoes not affect the formof the line element in this
view
Tolerance zone2 parallel lines 0.05apart
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R l #1 Eff t S f St i ht

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Rule#1s Effects on Surface Straightness
Whenever Rule #1 is in effect, an automatic indirectstraightens control exists for the surface line elements.
When the feature of size is at MMC, the line elements must beperfectly straight. As the FOS departs from MMC a straightness
error equal to the amount of the departure is allowed.
10.610.4
10.6max
Tolerance zone 2 parallel lines 0.2 apart
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Straightness at MMC Application
An importantbenefit becomesavailable whenstraightness isapplied at MMC:
extra tolerance ispermissible.
As the FOS
departs from MMCtowards LMC, abonus tolerancebecomes available.
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Definition: Circularity is a condition where all points ofa surface of revolution, at any Section perpendicular
to a common axis, are equidistant from that axis.
General representation:
CIRCULARITY
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A circularity controlis a geometric tolerancethat limits the amount of circularity on a part
surface.
It specifies that each circular element of a
features surface must lie within a tolerance
zone of two coaxial circles.
It also applies independently at each cross
section element and at a right angle to thefeature axis.
The radial distance between the circles is equal
to the circularity control tolerance value.
Circularity control :

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Circularity application:
1. Is to limit thelobing (out of
round) of a shaftdiameter.
2. In certain cases,
lobing of a shaftdiameter willcause bearingsor bushings tofail prematurely.
3. The diametermust be within itssize tolerance.
Tolerance zone is twocoaxial circles
OuterBoundary
0.3 tolerance zoneradial distance equal
to the circularitytolerance value 19

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Circularity application:
4. The circularitycontrol does not
override Rule #1.
5. The circularitycontrol tolerancemust be lessthan the sizetolerance.
6. The circularity
control does notaffect the outerboundary of theFOS.
Tolerance zone is twocoaxial circles
OuterBoundary
0.3 tolerance zoneradial distance equal
to the circularitytolerance value 20

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Cylindricity
Definition :Cylindricityis a condition of a surface of revolution inwhich all points of the surface are equidistant from a common axis.
General Representation :
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A cy l indr ic i ty contro lis a geometric tolerance that limits theamount of cylindricity error permitted on a part surface.
It specifies a tolerance zone of two coaxial cylinders within whichall points of the surface must lie. A cylindricity control appliessimultaneously to the entire surface.
The radial distance between the two coaxialcylinders isequal tothe cylindricity control tolerance value.
A cylindricity control is a composite control that limits thecircularity, straightness, and taper of a diameter simultaneously.
Cylindricity control :
Cylindricity application :
is to limit the surface conditions (out of round, taper, and
straightness) of a shaft diameter.
In certain cases, surface conditions of a shaft diameter willcause bearings or bushings to fail prematurely.
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Cylindricity application :
The diameter must also be within its size tolerance.
The cylindricity control does not override Rule #1.
The cylindricity control tolerance must be less than the total size tolerance.
The cylindricity control does not affect the outer boundary of the FOS. 23