1 DIMENSIONING AND TOLERANCING. 2 prismatic.sldasm.

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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