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DIMENSIONING AND TOLERANCING
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prismatic.sldasm
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DIFFERENT TYPES OF FIT
Clearance fit
Limits of size defined such that a clearance always results when mating parts are assembled
Interference fit
Limits of size are so prescribed that interference always results when mating parts are assembled.
Transition fit
Limits of size are so prescribed that either clearance or an interference may results when mating parts are assembled
Line fit
Limits of size are so prescribed that surface contact or clearance may result when mating parts are assembled
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BASIC HOLE SYSTEM
In the basic hole system the minimum (lower limit) hole size is taken as the basic size.
Stock hole is made “first” and then shaft is made to particular type of fit (to suit the hole).
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BASIC SHAFT SYSTEM
In the basic shaft system the maximum (upper limit) shaft size is taken as the basic size.
Stock shaft is created “first” and hole is made to particular type of fit (to suit the shaft).
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Basic shaft or basic hole?
In the basic hole system the minimum (lower limit) hole size is taken as the basic size.
Stock hole is made “first” and then shaft is made to particular type of fit (to suit the hole).
In the basic shaft system the maximum (upper limit) shaft size is taken as the basic size.
Stock shaft is created “first” and hole is made to particular type of fit (to suit the shaft).
IDENTIFY FIT SYSTEM
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“Shaft”
“Hole”
-- =
=
What type of fit is this?
IDENTIFY FIT SYSTEM
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IDENTIFY FIT SYSTEM
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IDENTIFY FIT SYSTEM
Basic hole
More commonly used
Basic shaft
Less commonly used
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Shown are limit tolerances
IDENTIFY FIT SYSTEM
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Surface roughness for different manufacturing methods
http://mdmetric.com/pdf/surfruff.pdf
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Φ
Basic hole fits
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Φ
Basic shaft fits
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Description of preferred fits
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ANSI PREFERRED HOLE BASIS METRIC CLEARANCE FITS
Pages 312, 313, 314, 315
ANSI PREFERRED SHAFT BASIS METRIC CLEARANCE FITS
Pages 316, 317, 318, 319
Engineering Design GraphicsJames LeakeJacob Borgerson
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cylindrical_metric.sldasm
Nominal diameter 25mm
Btw. what is wrong with this assembly?
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Loose running fit for nominal diameter 25mm preferred hole basic
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Free running fit for nominal diameter 25mm preferred hole basic
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Close running fit for nominal diameter 25mm preferred hole basic
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Sliding fit for nominal diameter 25mm preferred hole basic
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Locational transition fit for nominal diameter 25mm preferred hole basic
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Locational transition fit for nominal diameter 25mm preferred hole basic
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Locational interference fit for nominal diameter 25mm preferred hole basic
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Medium drive fit for nominal diameter 25mm preferred hole basic
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Force fit for nominal diameter 25mm preferred hole basic
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Hole is always the same: H7
We obtained the desired fit by changing shaft tolerance
