1. Made By:
VAIBHAV PARDESHI
LIMITS, FITS, TOLERANCES &
SURFACE ROUGHNESS

2.  It is impossible to maintain dimensions , geometrical
properties & surface roughness of components with
absolute accuracy in production process.
 Limits ,fits and tolerance are necessary to ensure
INTERCHANGEBILITY of mating parts , coupled with the
desired degree of tightness or looseness of assembly.
 Lack of tolerance leads to improper fits,it will also add to
delay & higher cost.
IT’s IMPORTANCE!!

3. INTRODUCTION
Basic Terms:
1) Nominal Size 2) Basic Size 3) Actual Size
4) Actual Deviation 5) Upper Deviation
6) Lower Deviation 7) Zero line

4.  The maximum and minimum sizes
permitted for a feature.
 There are two extreme possible
sizes of a component.
 The largest permissible size for a
component is called upper
limit and smallest size is
called lower limit.
Limits

5.  MAXIMUM LIMIT : The greater value is taken
as maximum limit.
 MINIMUM LIMIT : The smaller value is taken
as minimum limit.
 Eg. If basic size is Ø=30. then
30+0.035=30.035mm.

6. TOLERANCES
Definition: Algebraic difference between upper limit &
lower limit.

7. UNILATERAL TOLERANCES
1. Variation from the specified dimensions is
permitted in only one direction.
2.Either positive or negative but not both.

8. BILATERAL TOLERANCES
1. Variation is permitted in both positive and
negative directions from the nominal
dimension.

9. 1) Geometric tolerances are different from the tolerances
allowed for the size of feature, they specify the
allowable variation of the shape of a feature.
2) There are 3 basic types:
1.Form 2.Orientation 3.Position tolerances
3) Geometric tolerances are specified using a control frame
consisting of a tolerance symbol, a tolerance value &
optional datum planes.
GEOMETRIC TOLERANCES

10. GEOMETRIC TOLERANCE SYMBOLS

11. Fit is the degree of looseness
or tightness between two
mating parts
When FITS are combined
between shaft & hole they
can be classified into 3
categories:
1.Clearance Fit
2.Interference Fit
3.Transition Fit
FITS

12.  Always has a gap between two mating parts.
 Shaft size is small , compared to hole size.
 Generally in this type of fit, the lower limit size of the hole is
greater or at least equal to the upper limit size of the shaft.
 Use:- pivots , latches fit of parts exposed to corrosive
effects
Clearance Fit

13.  It is a fit where both clearance and interference may occur
in the coupling.
 Here tolerance zones of the hole and shaft are partly or
completely interface.
 Use:- Pulleys and bushing, Flushed bolts etc.
Transition Fit:-
B

14.  It always overlap & are used mainly for press fits where the
two parts are pushed together, and require no other
fasteners.
 The upper limit size of the hole is smaller or at least equal to
the lower limit size of the shaft.
 Use:-In bearing bushings,flanges etc.
Interference Fit:-

15. SYSTEM OF FITS

16. • The geometrical characteristics of a surface include,
1. Macro-deviations,
2. Surface waviness, and
3. Micro-irregularities.
• The surface roughness is evaluated by the height, Rt and
mean roughness index Ra of the micro-irregularities.
SURFACE ROUGHNESS

17. SURFACE ROUGHNESS NUMBER
• Represents the average departure of the surface
from perfection over a prescribed sampling length,
(usually selected as 0.8 mm)
• Surface roughness number (Ra) is expressed in
microns.
• Ra = (h1+h2+-----+hn)/n
• The measurements are usually made along a line,
running at right angle to the general direction of tool
marks on the surface.

18. INDICATION OF SURFACE TEXTURE
The basic symbol consists of two legs of
unequal length inclined at approximately 60’
to the line representing the considered
surface
The symbol must be represented by thin line
If the removal of material by machining is
required, a bar is added to the basic symbol,
If the removal of material is not permitted,
a circle is added to the basic symbol.
When special surface characteristics have to
be indicated, a line is added to the longer arm of
any of the above symbols,

19. Generally to indicate the surface roughness, the symbol is used instead of value.
The relation is given in following table.

20. CASE STUDY
Bearings on shaft

21. SELECTON OF FITS AND
TOLERACES
1.CONDITIONS OF ROTATION
a)Rotating load
b)Stationary load
c)Direction of load in determinant
2. MAGNITUDE OF THE LOAD
a)light load
b)normal load
c)heavy load
d)very heavy load
3. BEARING INTERNAL CLEARANCE
4.TEMPERATURE DIFFERENCES
5. DESIGN AND MATERIAL OF THE SHAFT AND HOUSING
6.EASE OF MOUNTING AND DISMOUNTING

24. For this example , we have selected m6 fit.
m- interference fit IT- 6grade
Shaft size= 70mm

25. Shaft diameter=70mm
Fit- m6 fit
Upper deviation(es)= +30
microns
Lower deviation(ei)= +11
microns
Basic size =70 mm
Final evaluation

26.  Design Data Book- PSG college
 Design Of Machine Elements-V.B. Bhandari
 Machine Design: Fundamentals and Applications- P.C.
Gope
 Machine Design-R.C.Patel
 MQC – Technical Publications
REFERENCES

27. THANK YOU