This document discusses anti-friction bearings used in machine tool design. It defines bearings and their purpose of allowing relative motion with minimal friction. It describes the broad classifications and types of ball and roller bearings, including deep groove ball bearings, self-aligning bearings, thrust ball bearings, angular contact ball bearings, cylindrical roller bearings, needle roller bearings, and tapered roller bearings. It discusses bearing requirements, types, dimensions, load capacities, lives, calculations, mounting, lubrication, and failure causes. It also covers spindle bearing arrangements and rigidity calculations.

1. MACHINE TOOL DESIGN - MECHANICAL
TOPIC : ANTI FRICTION BEARINGS
By:
HV RajaShekara
SENIOR DIRECTOR - Design Institute, IMTMA

2. BEARING
 Bearing is the mechanical element that
permits relative motion between two
parts, such as the shaft and the housing,
with minimum friction.
 Bearing ensures free rotation of the shaft
or an axle with minimum friction
 It supports the shaft or the axle and holds
it in the correct position
 It takes up the forces that act on the shaft
or the axle and transmits them to the
frame or the foundation.

3. BROAD CLASSIFICATION

4. TYPES OF BALL & ROLLER BEARINGS

5. NEEDLE ROLLER BEARINGS

6. ANTIFRICTION BEARINGS
Requirements:
• Have Rolling Elements
• Mostly Rolling contact with a small amount
of sliding contact resulting in almost constant
starting and running friction values
unaffected by variations in load, speed and
temperature. Meets requirement of
Machine Tools requiring frequent starting
and stopping.

7. ANTIFRICTION BEARINGS
• Require little lubricant and maintenance
• Occupy less axial space
• Expensive and noisier than journal bearings
• Subjected to Fatigue failure and have limited
life
• Bearings for radial load, axial load and
combined radial and axial loads

8. TYPES OF BEARINGS
Deep Groove Ball bearings
• Designed to carry radial load
• Can take up also thrust loads
to limited extent
• Can be lubricated and sealed
for life
• Single row bearings can
withstand small
misalignment.

9. TYPES OF BEARINGS
Self aligning bearings must be used for
large Misalignments.
Thrust ball bearings : carry purely thrust
loads.
Angular contact ball bearings : have high
radial as well as axial load capacity and
higher speed of operation.

10. TYPES OF BEARINGS
Roller bearings :
• Have much higher radial load
capacity due to greater contact area
• They cannot take up any Thrust
loads
• Their manufacturing requires
perfect geometry of the raceways
and rollers in order to keep rollers
from skewing and falling out of
alignment.

11. TYPES OF BEARINGS
• Roller bearings find more application in
Machine Tool Spindles
• For heavy loads and misalignments spherical
roller bearings must be used. Spherical
elements in addition have the advantage of
increasing their contact area as the load is
increased.

12. TYPES OF BEARINGS
• Needle bearings are very useful where high
radial capacity and minimum radial spare
are required.
• Tapered roller bearings combine the
advantages of ball and roller bearings in
that they can accommodate radial or
Thrust loads or combinations of both, and
in addition, the load carrying capacity is
high.

13. ANTIFRICTION BEARINGS
Dimensional and Running Accuracies:
• For interchangeability, the boundary dimensions
and tolerances are standardized by ISO.
• Radial Run out and side run out with respect to the
bore, groove run out with respect to the side of the
inner ring and outer ring, axial groove run out with
respect to the face.
• These specifications must be checked especially for
precision applications.

14. ANTIFRICTION BEARINGS
Load carrying capacity and life:
• Life as applied to bearings is the number of working
hours while running at constant speed, which the
bearing can complete before fatigue failure is
evident on one of the bearing rings or rolling
elements.
• The other causes of bearing failure that can be
avoided by precautionary measures are:

15. ANTIFRICTION BEARINGS
Causes of bearing failure:
• Incorrect mounting
• Carelessness during assembly
• Inadequate or unsuitable lubrication
• Incorrect sealing
• Wrong fits etc.

16. ANTIFRICTION BEARINGS
Basic Dynamic capacity C
is the constant load with which the bearing can
reach a normal life of 1 million revolutions.
For radial bearings the basic capacity corresponds to
pure radial load and for thrust bearings a centrally
acting pure thrust load.

17. ANTIFRICTION BEARINGS
Static carrying capacity Co.
• Is the load capacity of a bearing when the bearing is
not rotating, but in this case the load limit is based
not on fatigue considerations but on permanent
deformations or fractures formed on the load
carrying members of the bearing.
• The criterion for the load rating is about when the
deformation of the rolling element and track is
0.0001 of the rolling element diameter.

18. ANTIFRICTION BEARINGS
Life of bearing L=[C/P]p or C/P = L1/p
Where,
C = basic dynamic capacity of the bearing in kg,
P = equivalent bearing load in kg,
C/P = loading ratio, p =3 for ball bearings and
p =10/3 for roller bearings,
L = Life in millions of revolutions.

19. ANTIFRICTION BEARINGS
To obtain Life in working hours as a function
of the Life in millions of revolutions we have
the relation:
L = 60nLh
1000000
Where
Lh = nominal life in working hours, and n is the speed
in rpm.

20. ANTIFRICTION BEARINGS
• The loading ratio C/P can be read from the
Catalogues for different speeds and different lives,
separately for ball bearings and roller bearings.
The requisite bearing lives for different types of
machines depend on the following:
1. Type of machine tool
2. Whether SPM under constant conditions or
General purpose machine (GPM) with varying
conditions of machining. (continued)

21. ANTIFRICTION BEARINGS
3. The position in which the bearing is used.
4. The ease with which it can be replaced
5. For a Machine Tool working continuously for 8
hours a day at a constant load and speed life could
be taken as 20,000 – 30,000 hours.
A value of 50,000 to 60,000 hrs is required for
continuous working for 24 hours a day.

22. ANTIFRICTION BEARINGS
Lh = 100/  (Qi/Li)
Where :
Lh = over all life of bearing in hours
 represents the summation of Qi/Li for values of i
from 1 to n where
Qi are the respective percentages of total time for
which the loads Pi act and Li are the imaginary lives
in hours corresponding to the respective loads Pi
and speeds ni.

23. ANTIFRICTION BEARINGS
Calculation of Bearing Loads:
• In case of Static loading or in applications of very
small rotations or oscillations, the permissible
deformation is governed by rated static capacity.
• The equivalent static bearing Load-which is the
constant radial load (or axial load in the case of
thrust bearings) which would cause The same
deformation as the actual Load given by the
equation:

24. ANTIFRICTION BEARINGS
P = XFr + yFa
Where:
• P is the equivalent bearing load Fr is the actual
constant radial load.
• Fa is the actual constant axial load and X and Y are
the radial and thrust factors of the bearing
respectively.
• In the above equation, for pure radial load, Fa= 0
and Fr= P

25. ANTIFRICTION BEARINGS
• Thrust bearings are not suitable for high
speed applications.
• 1.6.3 Influence of speeds
• -High speed causes high temperature rise.
• - Reduces bearing capacity when beyond 100
C.
• - Lubrication problems even at low temp.

26. ANTIFRICTION BEARINGS
• - Radial ball bearings and cylindrical roller
bearings can be used at higher temperatures
than other types of bearings.
• n.dm < 500,000 – for deep groove ball
bearings cylindrical roller bearings & self
aligning ball bearings
• n.dm < 350,000 – for spherical roller bearings
and tapered roller bearings

27. ANTIFRICTION BEARINGS
• Influence of Mounting and Maintenance
•
• Open bearing types such as cylindrical roller
bearings, tapered roller bearings, separable
ball bearings etc. are recommended in cases
where mounting and disassembly are
frequent especially when the fits are tight.

28. ANTIFRICTION BEARINGS
• Mounting is easier also with the tapered adaptor
sleeves and removable sleeves.
• Self aligning bearings must not be used in cases
where they are not accessible during their assembly
with other parts, since outer ring gets cocked easily
hindering assembly.
• Ball bearings are less demanding from the point of
view of lubrication.

29. ANTIFRICTION BEARINGS
• In all other types of bearings, proper lubrication
systems must be used to provide circulation or
retention of the lubricant.
• Securing of bearings
• Radial securing by proper selection of fits for
bearing races.
• Axial securing – the bearings must be held axially
against the forces tending to move the bearing
races.

30. ANTIFRICTION BEARINGS
• The inner rings are made to sit against a
shoulder of the shaft and held in position by
a retaining ring or a shaft nut.
• When a step is not possible and the bearings
are spaced far apart, then a long spacer may
be used with a relief along the shaft length.

31. ANTIFRICTION BEARINGS
• If a power transmission element is mounted close
to the bearing in question, then a distance piece
may be introduced.
• If there is no axial load, shoulder abutment without
axial retention of the inner ring is permissible,
provided the outer rings are secured tightly against
the housing. Any thrust load is taken up by the
respective farther bearing.

32. ANTIFRICTION BEARINGS
In case of angular contact bearings and
taper roller bearings which are usually
secured using shaft nuts, it will be
expedient to use a standard lock washer
and an additional thin washer, in
between in order enable reliable
securing.

33. ANTIFRICTION BEARINGS
• In the case of short shafts, both bearings
must be used for locating the shafts, - one in
each direction.
• In some cases, the locating bearing may be
positioned by inserting one or two locating rings.
• In the case of cylindrical roller bearings with flanges
on only one side, the roller set can move laterally
on the track of the ring. Thus the outer rings are
always axially located Fig. 8

34. ANTIFRICTION BEARINGS
• Sealing of Rolling bearings
• Seals in bearings are helpful in retaining the
lubricant and preventing ingress of dirt entering
into the bearing elements.
• In places where effective sealing arrangements are
difficult within the spindle area, external sealing
arrangements are introduced outside the bearing
housing.

35. ANTIFRICTION BEARINGS
• Rubbing type seals provide effective sealing.
But introduce large friction torque and
heating.
• Labyrinth or clearance seals suitable for oil
and grease lubrication are applicable for high
speeds. Radial clearances of the order of 0.2
– 0.3 mm are to be maintained and any
collars located radially.

36. ANTIFRICTION BEARINGS
• The housings incorporating the seals should
be provided with adequate drainage
passages for the return of the oil to the base
of the bearing housing.
• Felt seals are employed when peripheral
speeds are less than 8 m/sec. Speeds of 10-
15 m/sec. are allowable for rotary shaft
seals.

37. ANTIFRICTION BEARINGS
• Bearing Mounting arrangements
• Table 2
• Preloading of bearings.
• Preloading of bearings is a method using which the
bearing deflection under the working loads is
reduced. A permanent axial load is applied for
adjusting the two bearings against one another.

38. ANGULAR CONTACT BALL BEARINGS
• BEARING ARRANGEMENTS

39. ANTIFRICTION BEARINGS

40. ANTIFRICTION BEARINGS
• In NNK type of double row cylindrical roller
bearings used on machine tool spindles, an
1:12 tapered bore in the inner ring is forced
against the corresponding tapered seating on
the spindle. The preloading thus created is
very steep. Care has to be taken to avoid
excessive load which will create overload and
over heating.

41. ANTIFRICTION BEARINGS
Rigidity Calculations for Machine Tool Spindles
• The Spindle running accuracy is influenced
by the elastic deformation of the Spindle, its
bearings, housings and other components of the
assembly.
• -The over all stiffness of the spindle system is
mainly affected by the stiffness of the bearings and
the spindle diameter. The housing stiffness has the
least effect.

42. ANTIFRICTION BEARINGS
• Thus we can write:
•  = 1 + 2 = P [(1/sA) {(a+L)/L}2 + (1/SB) (a/L)2
+ (a2/3E) (L/IL + a/Ia)]
• SA – Radial stiffness of the bearings nearer to
load P
• SB – Radial stiffness of the bearings farther to
load P
• a - overhang

43. ANTIFRICTION BEARINGS
• L – Span
• E – Youngs modulus of Elasticity
• IA – Area moment of Inertia of the
Section in the overhang region
• IL – Area moment of Inertia of the
Section in the Span region.

44. ANTIFRICTION BEARINGS
• In the above equation, if the bearings, diameter of
the Spindle and overhang of the Spindle are fixed,
then we note that the stiffness becomes a function
of the bearing span only. The optimum span Lo
based on Static stiffness that provides maximum
stiffness to the system can be derived as
• Lo  [6EIL(1/SA+1/SB)+(6EIL/a.SA)Q]1/3
• Where the iterative trial value Q is taken as 4a
initially and the value of Lo is derived.

45. ANTIFRICTION BEARINGS
• This derived value of Lo is used for Q in
subsequent iterations successively. A study
of the equation reveals that the effect of the
change of stiffness is more, when the span is
more than the optimum than when it is less.
For example when the span increases by 20%
beyond the optimum, the stiffness loss is
only 4%.

46. ANTIFRICTION BEARINGS
• Spindle bearing arrangements
The performance of a bearing arrangement in a
spindle being the main contributor to the quality of
work piece – tool complex, the spindle bearing
arrangement must posses the following
characteristics :
• Maximum rigidity : This is ensured by adequately
rigid spindle and by using bearings with minimum
deflections.

47. Types of Bearings
47

48. Types of Bearings (Contd.)
48

49. Types of Bearings (Contd.)
49

50. Cylindrical Roller
Bearing with
Taper Bore
Tapered Roller
Bearing
50

51. Contact
Angle
Contact Angle
Points of
Contact
51

52. Preload
Preload gap
52

53. Preload Gap
Preload
53

54. Preload
Gap
Back to Back Mounting
Preloaded
54

55. Preload Gap
Face to Face Mounting
Preloaded
55

56. Preload Step
Tandem Mounting
Preloaded
56

57. Contact Angle
Ball Screw Support Bearings
57

58. DB
Combination
DF
Combination
DT
Combination
Ball Screw Support Bearings
DUPLEX
58

59.  Pressure of oil is created within the bearing by the rotation of
the spindle. As the spindle rotates the oil in contact with the
spindle is carried into wedge-shaped cavities between the
spindle and the bearing. The oil pressure is increased as the oil
is forced through the small clearances between the bearing and
the spindle.
 The main limitation in a Hydro Dynamic Bearing is that a
definite clearance must be provided for the oil film to be
maintained between the spindle and the bearing.
Principles of Hydro Dynamic Bearing
59

60.  This clearance may result in the centre of a spindle in the
bearing to change its position owing to variation in the
applied force. Clearances normally provided between the
spindle and the bore of the bearing for oil film vary from 50
to 100 Microns depending upon the diameter of the journal.
Principles of Hydro Dynamic Bearing
(contd.)
60

61. Principle of Hydrodynamic bearings
Oil Exhaust
Oil Pocket
61

62.  For a hydrostatic bearing, the spindle is supported by a
relatively thick film of oil supplied under pressure , similar to
that used in the bearings for linear movements.
 The oil is pressurised by a pump external to the bearing.
Hydrostatic Bearings
62

63.  The load carrying capacity of this type of bearing is
independent of the rotational speed. They have high
damping properties, high running accuracy, high wear
resistance but are very expensive. These are used where
temperature effects cause problems in the part accuracy as
in the case of grinding machines and fine boring machines.
Principles of Hydrostatic Bearing
63

64. Oil Inlet
Oil Exhaust
High Oil
Pressure
Principle of Hydrostatic Bearings
64

65.  The ball and roller bearings have some amount of axial and
radial clearances. When a main spindle is mounted on the
bearings there should not be any axial or radial play in the main
spindle assembly. To achieve this the clearances in the bearings
have to be taken up by preloading them .
 In case of tapered roller bearings and angular contact ball
bearings, the axial and radial clearances can be taken up
simultaneously by preloading. Cylindrical roller bearings
(Double row ) with tapered bore are radially preloaded by
pushing the inner race against the taper on the spindle.
Preloading
65

66.  On the main spindle the following accuracies are defined
 Radial Run Out
 Axial Run Out
 The accuracy of spindle during running depends on the thermal
stability of the spindle. This is the most important aspect of spindle
design, especially for high speed and high accuracy spindles.
Considering the above, appropriate bearing lubrication and spindle
cooling systems should be adopted in the design of spindle for
machine tools.
Machine Tool Spindle Accuracy
66

67. Deflection Curve as a Function of the Load
67

68. Deflections and Axial Loads forVarying Contact Angles
68

69. BEARING NUMBERING SYSTEM
B 70 8 C T P4S U L
TYPE Standard Preloads
B Standard L - Light
OR relieved M - Medium
IR Symmetrical H - Heavy
HCB Standard Bearing Sets
OR relieved U - Single Bearing
IR Symmetrical Universal
Ceramic Balls DU - Duplex Set
HS High Speed Small Universal
Ball Bearing TU - Triplex Set
Double Relieved Universal
HSS High Speed Bearing QU - Quadruplex Set
Sealed Universal
HC High Speed Ball PU - Pentaplex set
Bearing, Ceramic Balls Universal
HCS High Speed Ball DB - Duplex Set
Bearing, Ceramic Balls Back to Back
Sealed DT - Duplex Set
Tandem
SERIES TBT - Triplex Set
719 Light Series Tandem, Back to Back
70 Medium Series QBC - Quadruplex Set
72 Heavy Series Double Tandem
Back to Back
BORE DIAMETER
oo 10 mm PRECISION
o1 12 mm P4S - FAG Tolerance,
O2 15 mm better
thanISO P4
O3 17 mm
O4 4 x 5 20 mm CAGE
O5 5 x 5 25 mm T - Phenolic, OR Riding
CONTACT ANGLE M- Metalic, Brass
C 150
E 250
69

70. BEARING NUMBERING SYSTEM
B 70 8 C T P4S U L
TYPE
B Standard, OR Relieved
IR Symmetrical
HCB Standard, OR Relieved
IR Symmetrical, Ceramic Balls
HS High Speed Small Ball Bearing
Double Relieved
HSS High Speed Bearing Sealed
HC High Speed Ball Bearing
Ceramic Balls
HCS High Speed Ball Bearing,
Ceramic Balls, Sealed 70

71. BEARING NUMBERING SYSTEM
B 70 8 C T P4S U L
SERIES
719 Light Series
70 Medium Series
72 Heavy Series
Bore Diameter
oo 10
o1 12
o2 15
o3 17
o4 4x5 = 20
o5 5x5 = 25 mm 71

72. BEARING NUMBERING SYSTEM
B 70 8 C T P4S U L
CONTACT ANGLE
C 15o
E 25o
CAGE
T Phenolic OR Riding
M Metal (Brass)
PRECISION
P4S FAG Tolerance. Better than ISO P4
72

73. BEARING NUMBERING
SYSTEM
B 70 8 C T P4S U L
BEARING SETS
U - Single bearing, Universal
DU - Duplex Set, Universal
TU - Triplex Set, Universal
QU - Qudruplex Set, Universal
PU - Pentaplex Set, Universal
DB - Duplex Set, Back to Back
DT - Duplex Set, Tandem
TBT - Triplex Set, Tandem, Back to Back
QBC- Qudruplex Set,
Double Tandem, Back to Back 73

74. BEARING NUMBERING SYSTEM
B 70 8 C T P4S U L
Standard Preloads
L - Light
M - Medium
H - Heavy
74

75. BEARINGS PRECISION GRADE
RHP ISO ABEC
PO Normal 1
P6 6 3
P5 5 5
P4 4 7
P3 P4/P2 P4/P2
P2 2 9
75

76. THANK YOU