Tolerance,Fits & Assembly

8/2/2019 Tolerance,Fits & Assembly

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Presented by group 2:

Nguyn LongNguyn Trung Vit


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Chapter ObjectivesAfter completing this chapter, we will be able to:

Demonstrate the proper way to specify units of measurement.

Identify the basic concept of tolerance and assembly.

Demonstrate the proper way to specify dimensions and tolerances.

Do some simple exercises and check the result with computer.


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Units of Linear Measurement:

Linear measurement

Inch system Metric system


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Fundamental drawing rule

Inch system Metric system

A zero is never placed beforethe decimal point for value lessthan one inch.

A dimension is specified withthe same number of decimalplace as its tolerance even if

zeros need to be added to theright of decimal point

A zero is placed beforethe demical point for valueless than one milimeter.

Zeros are not added tothe right of the demicalpoint when dimensions

are whole number plussome decimal fraction of amilimeter


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Fundamental drawing rule


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Size Designations

Nominal size: It is the designation used for general identification and is usuallyexpressed in common fractions.


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Size Designations

Actual size: is the measured size of the finished part.


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Size Designations

Limit dimension

Maximum limit of sizeHole: DmaxShaft: dmax

Minimum limit of sizeHole: DminShaft: dmin

m axm inddd

real


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Limit deviation

Deviation is positive and also negative.

Lower deviation: is the difference between the nominonal size and theminimum permitted size of the part.

Upper deviation: is the difference between the nominonal size and thepermitted maximum size of the part.


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Limit deviation


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Tolerance fundamental

Tolerance is the differencebetween the permitted minimumand maximum sizes of a part.

Tolerance is denoted by

A number symbol (the grade)A letter symbol

Hole: Capital letters.Shaft: Small letters.


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Tolerance fundamental


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ASSEMBLY AND FIT

Asembly :the process of putting together a number of parts to make a machine or

other products


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ASSEMBLY AND FIT

1:Wrapping surface (B mt bao)2:Wrapped surface (B mt b bao)

Fit:tightness or looseness of combination of parts.


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Type of fit (based on the surface)

ASSEMBLY AND FIT

1)Plain surface fit (bmttrn)

4- pttng, 5- xilanh

Plain cylinder fit (trtrn) Smooth fit (bmtphng)


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ASSEMBLY AND FIT

2)Thread fit (lp ghp ren)


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3)Gear Drive fit (lp ghp truynng bnh rng)

ASSEMBLY AND FIT


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We can divide the plane surface fit into 3 group:

ASSEMBLY AND FIT

The clearance fit The transition fit The interference fit

Always have aspace between

parts

Always an actual

interference of

material

Either a clearance

or interference

condition


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ASSEMBLY AND FIT

Important equation:

1. Clearance fit the difference between the sizes of the hole

and the shaft, before assembly.

S=D-d

=>Smax = Dmaxdmin Smin = Dmindmax

Tolerance of the clearance:TS = Smax Smin

= ( Dmax dmin ) (Dmin dmax )

= ( Dmax Dmin ) + (dmax dmin )

TS = TD + Td


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2.Transition fit:

Tolerance:

TN,S = Nmax + Smax

TN,S = TD + Td

ASSEMBLY AND FIT


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3.Interference Fit:

Allowance

(the minimum clearance space

or maximum interference)

Tolerance:

ASSEMBLY AND FIT

N d D

max max min N d D

min min max N d D

max min

2m

N NN

max minNT N N

N D d T T T


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Distributive graph of the region of the fitting tolerance:

(s phn b dung sai)-The zero line:the nominal size.

-The vertical axe: the deviation.

Ex1:d=D=40mm

Hole:ES=25 m;EI=0 m;

Shaft:es=-25 m;ei=-50 m;

=>Clearance fit

=>Smax =75 mSmin =25 m

( H7:F7)

ASSEMBLY AND FIT


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ASSEMBLY AND FIT

EX2:D=d=82mm,ES=35 m,EI=0 m,es=45 m,ei=23 m

Draw the diagram,caculate ,tolerance andallowance.(H7:n6)

Solution:

m inm axm inm ax ,,,ddDD

mmDdN

mmdDSAllowance

mmTTT

mmeiesT

mmEIESTTolerance

mmmmmmeidd

mmmmmmesdd

mmmmmmEIDD

mmmmmmESDD

DdSN

d

D

045.082045.82

012.0023.82035.82:

057.0035.0022.0022.0023.0045.0

035.00035.0:

023.82023.082

045.82045.082

82082

035.82035.082

m inm axm ax

m inm axm ax

,

m in

m ax

m in

m ax

Transition fit


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ASSEMBLY AND FIT

DO IT YOURSELF:From the plot,caculate:

minmaxminmaxminmax ,,,,,,,,,,,,,, NNTTTddDDeiesEIESdD dDNN

Solution:

mmNmmN

mmTmmT

mmTmmdmmd

mmDmmDmeimes

mEImESmmdD

d

D

NN

009.0;05.0

;041.0;016.0

;025.0;034.45;05.45

;45;025.45;34;50

;0;25;45

minmax

minmax

minmax


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Tolerance,Fits & Assembly

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