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Tolerances
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Tolerance The total amount a specific dimension can
vary. (ANSI Y14.5M1!!4"
Tolerances are assi#ned so that any t$omatin# parts $ill fit to#ether.
%i#hly accurate parts are e&tremelye&pensive' so tolerances should e as
#enerous as possile $hile still maintainin#proper function for the part.
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Limit Dimensions
)imit dimensions specify the upper and lo$er value.An acceptale part may e at the upper limit' lo$er limit' or
any value in et$een.
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Allowance & Fit
The minimum clearance space or ma&imum interference is
the allowance. Fitis the ran#e of ti#htness or looseness
et$een parts for their function.
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Types of fit *learance fit+internal memer al$ays has space orclearance.
Interference fit+internal memer is al$ays lar#er and has to
e forced inside e&ternal memer.
Transition fit+either clearance or interference.
)ine fit+clearance or surface contact results.
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Basic Hole System %ole $ill e machined
$ith a standard si,edtool.
-etermine type of fitnecessary. se fit taleor other$ise determineallo$ance.
Apply tolerances usin#hole si,e as asicdimension.
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Basic Shaft System )ess commonly
used than asic holesystem.
Most commonlyused $hen manyparts $ill fit on a
standard shaft. Shaft si,e is asic
dimension.
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Plus/minus dimensioning /asic si,e of dimension is #iven $ithtolerances e&pressed as a plus0minus ran#e.
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!ual Bi"lateral Tolerances
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Baseline #s$ %ontinued /aseline tolerances dont 2stac3up
*ontinued (chained" tolerances 2stac3
up
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etric Tolerance Terminology
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Basic Hole ethod' T()% The 1 InternationalTolerance (IT" #radesvary accordin# to theasic si,e.
% indicates tolerance isfor hole asis. 6 is forshaft asis.
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*eometric Dimensioning & Tolerancing
uses standard symols to indicate tolerancesthat are ased on the features #eometry.
sometimes called feature ased dimensionin#7 tolerancin# or true position dimensionin# 7tolerancin#
uses feature control frames to indicatetolerance
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* D & T Sym+ols
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,nderstanding Tolerance -ones Traditional plus0minus type of tolerancin# descries a
s8uare ,one for acceptale locations.
9-7T descries a ,one around the theoretically e&act
location for the feature.
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Basic Dimension A theoretically e&act
dimension used to
locate features in9-7T
/asic dimensions
are untoleranced.
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Datums -atums are features
on the o:ect that are
used as reference
surfaces from $hichother measurements
are made.
Not every 9-7Tfeature re8uires a
datum.
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%ylindrical Tolerance -one
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a.imum aterial %ondition Ma&imum material condition for a hole feature isthe smallest si,ed hole.
Ma&imum material condition for a shaft feature is
the lar#est shaft. The ma&imum material condition modifier in a
feature control frame means that the toleranceapplies at ma&. material condition. If the actual
hole is lar#er than the smallest allo$ale hole' aonus tolerance can e added to the statedtolerance value.
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a.imum aterial %ondition
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Traditional methods for tolerancin# an#les re8uire that an#led surfacese very accurate near the verte& of the an#le' ut can vary morealon# the len#th of the an#led feature.
Angular Tolerances
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*D&T Angular Tolerance -ones
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%oncentricity
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Summary There are several methods you can use to
specify tolerances in a dra$in#.
)imit tolerances #ive the upper and lo$erran#e for a dimension
;lus0minus tolerances #ive the nominal orasic si,e and a plus and0or minus ran#e for
the tolerance. 9-7T uses symols to descrie tolerance
,ones ased on #eometric features.