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TRANSCRIPT
Lecture 7
Terminology
Types of Fits
Tolerance grades: There are 20 international tolerance grades
Fits• A fit is a shaft and a hole designation• H7f8• H,h is a zero based designation • The capital letter is for holes and small
letter is for shafts• In hole based system H is found and in
shaft based systems h is found. The number after the grade is the tolerance grade
Types of fits and their designations
3
2
3
21
#)()(001.045.0
Di
ikITmimmDDDi
DDD
In numbers and equations
The most commonly used grade numbers are IT6 through IT16, and these are based on the Renard R5 geometric series of numbers. For these, the basic equation is
where D is the geometric mean of the size range under consideration and is obtained from the formula
The ranges of basic sizes up to 1000 mm for use in this equation are shown in Table
With D determined, tolerance grades IT01 through IT16 are found using Eq.and the following table
Design a loose fit for a basic size of 121mm
mmshaft
mDdeviationupperc
mmmmHole
miITcHfitrunningLoose
mi
mmxD
762.120788.120)252.0212.0(212.0(121
2128.095
25.121121)252.000.0(121
252100*52.2100111111
52.2)96.146(001.096.14645.0
96.1461801203
Design an easy running for a basic size of 130 mm
)063.0042.0(042.0(13055.425.5
063.130130)063.000.0(130
6325*52.225888
52.2)96.146(001.096.14645.0
96.146180120
41.0
3
shaftmDdeviationupperc
mmmmHole
miITfHfitrunningeasy
mi
mmxD
Useful link:
http://www.roymech.co.uk/Useful_Tables/ISO_Tolerances/ISO_LIMITS.htm