This manual provides an overview of centerless external cylindrical grinding, covering the fundamentals, advantages and disadvantages, machine concepts, and key principles like infeed and throughfeed grinding. It aims to serve as a compact reference for both novices and experienced operators, emphasizing productivity and process knowledge. The document contains extensive details, formulas, and diagrams related to the grinding process and its various parameters.

1. A member of the United Grinding Group
Centerless external cylindrical grinding
Manual

2. 2nd edition
June 2016
Liability disclaimer:
Subject to technical and other changes.
All information and recommendations have been compiled up to the time of printing
to the best of our knowledge and belief and perceived as correct. Nevertheless, any
liability for errors in the information is excluded.
Authors: Dipl. Technical Editor (FH) Kristian Conrad
Sven Stoll
Dipl.-Ing. Karsten Otto
Copyright: Schaudt Mikrosa GmbH
Saarländer Strasse 25
04179 Leipzig · Germany
sales@schaudtmikrosa.com
www.schaudtmikrosa.com

3. 3
Contents
Preface7
Fundamentals9
1.1 What is centerless external cylindrical grinding? 10
1.1.1 Functional principle 10
1.1.2 Infeed grinding and throughfeed grinding 12
1.2 Advantages and disadvantages 14
1.2.1 Advantages over grinding between centers 14
1.2.2 Disadvantages over grinding between centers 15
Machine concepts 17
2.1 Classification according to inclination of the
machine bed 18
2.2 Classification according to grinding zone 18
2.2.1 Moving grinding zone 19
2.2.2 Stationary grinding zone 20
2.3 Spindles 22
2.3.1 Spindle bearing principle 22
2.3.2 Wheel mounting 25
2.3.3 Spindle bearings 25
The grinding zone 27
3.1 Center shift 28
3.2 Shaping process 29
3.2.1 Roundness 29
3.2.2 Determining the roundness error 30
3.2.3 Height position H and mounting angle β 31
3.2.4 Polygons 33
3.2.5 Stability index SI 35
3.2.6 Stability cards 37

4. 4
3.3 Grinding zone geometry 40
3.3.1 Tangent angle γ 40
3.3.2 Height position H 41
3.3.3 Angle at the contact points 41
3.3.4 Relative support angle βrel
42
3.3.5 Grinding zone geometry during infeed grinding 42
3.3.6 Grinding zone geometry during throughfeed grinding 44
3.4 Forces in the grinding zone 46
3.4.1 Forces on the grinding wheel 47
3.4.2 Forces on the workpiece support 48
3.4.3 Forces on the regulating wheel 49
3.4.4 Consideration of the forces 50
Infeed grinding 53
4.1 General principle 54
4.2 Process control 54
4.2.1 Grinding from solid stock 56
4.2.2 Grinding with additional functions 57
4.2.3 Oscillation 58
4.2.4 Influence of the workpiece geometry 58
4.3 Grinding zone layout 59
4.3.1 Undercuts and spacers 59
4.3.2 Stop 61
4.3.3 Initial grind 63
4.4 Grinding of end surfaces 64
4.4.1 Inclination of the grinding wheel 65
4.4.2 Inclination of the workpiece support 66
4.4.3 Axial plunging in straight plunge with Z-axis 67
4.5 Removal of workpieces 68
Throughfeed grinding 69
5.1 General principle 70
5.2 Shape of the regulating wheel 71
Contents

5. 5
5.2.1 Conical regulating wheel shape 74
5.2.2 Symmetric regulating wheel shape 77
5.2.3 Numerically controlled regulating wheel shape 79
5.2.4 Stagnation point offset 80
5.3 Process control and wear development 82
5.3.1 Multiple passes 83
5.3.2 Single-stage process (swivelling the regulating
wheel) 84
5.3.3 Multiple-step process (profiling of grinding wheel) 85
5.3.4 Conicity of the grinding zone 86
5.4 Guidance of workpieces 88
5.4.1 Guide jaws and gibs 88
5.4.2 V-block workpiece support 90
5.4.3 Upper guide 91
Influencing factors 93
6.1 System parameters 94
6.1.1 Infeed grinding 94
6.1.2 Throughfeed grinding 95
6.2 Control variables 97
6.2.1 Grinding wheel rotational speed nS
and
Grinding wheel circumferential speed vS
98
6.2.2 Regulating wheel rotational speed nR
and
Regulating wheel circumferential speed vR
99
6.2.3 Workpiece rotational speed nW
and
Workpiece circumferential speed vW
100
6.2.4 Infeed ae
and infeed rate vfr
during infeed grinding 102
6.2.5 Feed s and feed rate vfa
during throughfeed grinding 105
6.2.6 Number of grinding passes U and grinding time ts
106
6.2.7 Sparking-out revolutions Ua
and sparking-out time ta
107
6.3 Indicators 108
6.3.1 Speed ratio qS
108
6.3.2 Relative stock removal rate Q´W
109
6.3.3 Equivalent cutting thickness heq
111
Contents

6. 6
6.3.4 Grinding ratio G 113
6.4 Process design 114
6.4.1 Strategy for specification of reference values 114
Symbols and units 117
Glossary121
Index127
Bibliography133
Contents

7. 7
We at Schaudt Mikrosa GmbH have decided to describe the most
relevant information about the centerless grinding process. Due to
the wealth of information and the limited space, however, we do
not claim to be exhaustive.
This guide is intended to give a quick introduction to a complex
subject. It summarizes as a compact reference the most important
relationships in centerless grinding. However, with its comments,
formulas, tables and diagrams, it should also be of help to expe-
rienced grinders.
The guide does not have to be read linearly and therefore often
contains references to further information in other chapters. A
quick access to key information is provided by the glossary, the
section on formula symbols and units, as well as the index in the
Appendix.
Centerless external cylindrical grinding has established itself in
the past as a successful grinding process mainly because of its
high productivity.
Also in the future, further increases in productivity can be ex-
pected, in particular through the use of CBN. With new machine
concepts and advances in grinding technology, ever smaller geo-
metrical and positional tolerances become possible. Centerless
grinding is already increasingly used in small series batches. Ho-
wever, it requires comprehensive process knowledge by the ma-
chine operator and setup technician.
Your Schaudt Mikrosa GmbH
… only called cen-
terless grinding
hereunder
… Cubic Boron
Nitrite: Extremely
hard grinding abra-
sive for highspeed
applications to
reduce cycle times
Preface

8. 8

9. 9
The following chapter provides in brief form the fundamentals of centerless external
cylindrical grinding. It should help to gain a quick overview of the many relationships.
Exact details of the different variables can be found in further chapters.
1
Fundamentals
Centerless external cylindrical
grinding
Introduction
Relationships
Fundamentals
Workpiece support
Regulating wheel
Grinding wheel

10. 10
1.1 What is centerless external cylindrical grinding?
Centerless grinding is a method of grinding cylindrical bodies. It
is used for mass production of cylindrical rollers, tapered rollers,
jet needles, pump pistons, hydraulic valves, journal crosses, drills,
etc.
1.1.1 Functional principle
The workpiece is not clamped between two centers, which is why
it is referred to as centerless grinding. Instead, the workpiece
lies in the so-called grinding zone between the grinding wheel
and the regulating wheel on a workpiece support. The workpi-
ece is rotated and stock is removed by the spinning grinding wheel
and regulating wheel (Fig. 1-2).
Fig. 1-1
Selection of
some products
of centerless ex-
ternal cylindrical
grinding
1 Fundamentals | What is centerless external cylindrical grinding?

11. 11
Fig. 1-2
Principle of
centerless ex-
ternal cylindrical
grinding
The grinding pressure of the grinding wheel [1] pushes the work-
piece [2] against the regulating wheel [3] and the workpiece
support [4]. The rotating regulating wheel provides the backpres-
sure necessary for grinding.
The regulating wheel and grinding wheel have the same direction
of rotation but different rotational speeds. The regulating wheel
rotates at a lower speed, thereby slowing the workpiece.
In addition, the regulating wheel supports the workpiece and
determines during throughfeed grinding, by its inclination in its
rotary axis and rotational speed, the throughfeed speed of the
workpiece.
The rotating workpiece lies on the workpiece support during grin-
ding. The support influences the quality of the grinding process
due to its thickness, the support angle β and the material used for
the contact surface.
What is centerless external cylindrical grinding? | 1 Fundamentals
[1] Grinding wheel
[2] Workpiece
[3] Regulating wheel
[4] Workpiece support
... also referred to
as positioning rail

12. 12
1.1.2 Infeed grinding and throughfeed grinding
A distinction is made in centerless external cylindrical grinding
between two methods: Infeed grinding and throughfeed grin-
ding.
1 Fundamentals | What is centerless external cylindrical grinding?
Infeed grinding Throughfeed grinding
Roughing Finishing Sparking-
out
Application area: Workpieces with
stepped or profiled lateral surfaces
The workpiece is inserted from the
top or the side into the grinding zone
and positioned by an axial stop. This is
achieved by a slight inclination of the
regulating wheel (0.1°–0.2°).
Application area: Cylindrical, non-
profiled workpieces such as rings, bars,
pins and pipes
The workpieces run continuously
through the grinding zone by axial feed
force. This is made possible by the incli-
nation of the regulating wheel about its
rotational axis.
To ensure that, despite this inclination,
all workpieces have contact across
the entire wheel width, the regulating
wheel has a hyperbolic shape (fig.
above).
Tab. 1-1
Infeed grinding
and throughfeed
grinding

13. 13
↑ Chapter 4
Infeed grinding
↑ Chapter 5
Throughfeed
grinding
↑ Section 4.4
Grinding end
surfaces
Infeed grinding Throughfeed grinding
The grinding wheel determines the
shape of the workpiece and therefore
has a corresponding profile. Also the
regulating wheel is profiled according
to the workpiece contour in order to
support the workpiece.
Several seats of a workpiece can be
ground simultaneously and without
interfering with each another. If the
grinding zone is wide enough, even
multiple workpieces can be in the
grinding zone.
Special case: Angular infeed grinding
(even end surfaces can be machined)
The rotational speed and the angle
of inclination of the regulating wheel
together determine the feed rate of the
workpieces.
The workpieces contact each other
with their end surfaces until they pass
through the last section of the grinding
zone. At this point, the circumferential
speed of the regulating wheel is high-
est, because its circumference is largest
here (fig. above).
The machining process is extremely
economical, because the feeding of the
machine is carried out during grinding.
Infeed motions are necessary only inso-
far as they are required to compensate
the wear of the grinding wheel.
Special case: Throughfeed grinding of
tapered rollers and cambered cylindrical
rollers
What is centerless external cylindrical grinding? | 1 Fundamentals
… feeding the
machine with
new blanks
Tab. 1-1 Continued
Infeed grinding
and throughfeed
grinding

14. 14
1.2 Advantages and disadvantages
Each grinding method has its advantages and disadvantages. The
comparison below explains the specific advantages of centerless
external cylindrical grinding over conventional grinding between
centers.
1.2.1 Advantages over grinding between centers
High productivity: Clamping of workpieces is unnecessary. This
results in very low secondary times during insertion and remo-
val of workpieces. The secondary times are usually much smaller
compared to clamping between centers. In centerless throughfeed
grinding, one workpiece immediately follows the other. The secon-
dary time for feeding is therefore very low.
Stable support of the workpiece: The workpiece is supported
by the regulating wheel and the workpiece support over a substan-
tial part of its length or over its entire length. This is extremely
advantageous particularly for longer workpieces with very small di-
ameters. Vigorous rough grinding is possible without considering
bending and torsional stresses. Harmful deformities by the grinding
forces do not occur. As a result, the stock removal rate can be
increased. During finish grinding, the stable support of the work-
piece allows very precise grinding, i.e. even workpieces with low
tolerances are machined reliably.
Double precision: The adjusted infeed amount corresponds to
the diameter reduction of the workpiece during centerless grin-
ding. When grinding between centers, however, the infeed amount
is radial. This means that at the same infeed amount the diameter
is reduced by approximately double the amount. The basic accura-
cy of the process is thus much higher in centerless grinding. Infeed
errors, caused, for example, by grinding wheel wear or thermal
… time which
cannot be used for
grinding itself, but
is necessary
1 Fundamentals | Advantages and disadvantages
… a grinding pha-
se, such as finish
grinding; more in
the glossary

15. 15
displacements in the machine, are only half as large.
Reduced preparatory work: Preparation of the workpiece by
making the centerings, as required for grinding between centers,
is unnecessary.
Lower allowance: In centerless grinding, the workpiece seeks
its rotary axis at the beginning of machining according to the exi-
sting lateral surface. Since the highest points on the workpiece
come in contact first here, the largest diameter possible in the
respective condition is ground and finished in centerless grinding.
This means that the allowance for centerless grinding can be less
than for grinding between centers, as the required allowance de-
pends there on the centering position relative to the outer surface.
1.2.2 Disadvantages over grinding between centers
Regenerative effect: This effect may cause unstable behavior
during the shaping process. However, the relationships have been
well known for some years and can be controlled by choosing a
suitable grinding zone geometry.
Problems with coaxiality/ concentricity: There is no concen-
tricity of the outer surface to centering holes that may exist on
the workpiece. This may cause problems if subsequent steps are
working again from the center. This effect can be influenced with
the KRONOS dual.
↑ Section 3.3
Grinding zone
geometry
… entire machi-
ning allowance of
a workpiece
Advantages and disadvantages | 1 Fundamentals
… more about
coaxiality and
concentricity in
the glossary

16. 16
Lower flexibility: Changeover to another type of workpiece is
– due to handling of partly rather large grinding and regulating
wheels – quite time-consuming. At least in plunge grinding, a
workpiece support customized for the workpiece is required.
No grinding in opposite direction: Grinding in the opposite
direction is not possible. The frictional force on the regulating
wheel is not sufficient to overcome the friction of the
workpiece support as well as the cutting force on the grinding
wheel.
… grinding wheel
and workpiece
run in opposite
directions at their
contact point
1 Fundamentals | Advantages and disadvantages

17. 17
To meet the various demands for the centerless external cylindrical grinding, diffe-
rent machine concepts are in use. The major ones are mentioned below and their
advantages and disadvantages are explained briefly.
2
Machine concepts
Machine types
Machine bed
Cross slide
Spindles
Bearings

18. 18
2 Machine concepts | Classification according to inclination of the machine bed
Horizontal Angular Vertical
• Most usual model
• Good accessibility during
dressing
• Application at MIKROSA
• Suitable for heavy
workpieces, as a part of
the weight is shifted to
the regulating wheel
• Avoidance of abrasion as
workpiece is supported
while it is being turned
• Special construction
• Advantages in the hand-
ling of heavy workpieces
• Only „grinding under the
center“ is possible
• Higher contact pressure
between workpiece and
regulating wheel
2.1 Classification according to inclination of the ma-
chine bed
When machines are classified according to their bed inclination,
three types can be distinguished:
2.2 Classification according to grinding zone
Another feature of classification is the grinding zone. A distinction
is made between machines with moving and stationary grinding
zone. The latter includes also special cases such as dual grinding
and the cross slide principle.
Tab. 2-1
Classi-
fication
according
to inclina-
tion

19. 19
Classification according to grinding zone | 2 Machine concepts
2.2.1 Moving grinding zone
In this principle, the grinding spindle head is permanently con-
nected to the machine bed. All three movable slides (X1, X4, B1)
are located on the side of the regulating wheel. The system is
therefore also called a „3-slide system“.
Compact design
Very high rigidity of the grinding wheel side
Cost-effective production since no complex infeed slide is
required for the grinding wheel side
Reduced rigidity of the regulating wheel side by several slide
guides
Handling must be tracked with high effort, because the work-
piece support is moving due to grinding wheel wear
B
1
B
1
X4
-
+
X4
-
+
X1
-
+
X1
-
+
--
X2X2
+ Z2Z2
+
-
X3
-
+
X3
-
+
Z3
-
+
Z3
-
+
Fig. 2-1
Moving grinding
zone

20. 20
2 Machine concepts | Classification according to grinding zone
… machines con-
nected in series
Fig. 2-2
Stationarygrinding
zone
2.2.2 Stationary grinding zone
The workpiece support is stationary or minimally swivellable (B1-
axis) in the center of the machine. Both the grinding wheel and the
regulating wheel have their own axis slides by which they can be
moved to the workpiece support.
Handling need not be carried along
a advantageously especially with interlinked machines
Feeding during throughfeed grinding can be absolutely linear
a important for machining of long workpieces
Good accessibility a quick and flexible changeover possible
Reduced rigidity of the grinding wheel side, because the
grinding spindle is not firmly connected with the machine bed
More time-consuming and thus more costly
Large space requirement
B
1
B
1
X4
-
+
X4
-
+
X1
-
+
X1
-
+
X2X2
+
-
+
-
+
-
Z2Z2
X3-
+
X3-
+
Z3
-
+ Z3
-
+

21. 21
The cross slide principle and dual grinding are considered special
cases of the stationary grinding zone:
Cross slide principle
In this machine concept, the grinding wheel and regulating wheel
are arranged, together with their drives, on cross slides. As the
name suggests, these slides can be moved both along the X-axis
and the Z-axis. The dressers are fixed in the center of the machine.
Dressing at workpiece level results in higher dressing precisi-
on
The machine with its 4 axes has the same functionality as
conventional designs with 7 axes
Cross slides need more space, resulting in a wider machine
a restricted wheel widths
No CD dressing possible
Fig. 2-3
Cross slide
principle
X4
-
+
X4
-
+
X1
-
+
X1
-
+
+
-
+
-
Z4
-
+
Z4
-
+
Z1Z1
Classification according to grinding zone | 2 Machine concepts
… dressing
during the grinding
process

22. 22
2 Machine concepts | Spindles
Dual grinding
Dual grinding combines grinding between centers and centerless
grinding on one machine. The workpieces are first ground between
centers and then placed in the grinding zone for centerless grin-
ding.
Good coaxiality from the centering to the outer surface by
grinding between centers
Short grinding time and high accuracy by subsequent center-
less grinding
Stable support by the regulating wheel
Complex design with additional axis and spindle
Reduced accessibility and wider machine
Increased setup effort
2.3 Spindles
The spindles for the grinding and regulating wheels are essential
core components of the machine. Since the design of these spind-
les has a significant impact on the grinding process, its bearing
and support principle are part of the next sections.
2.3.1 Spindle bearing principle
The spindles of the grinding and regulating wheels are supported
either on one side (floating bearing) or on both sides (gantry be-
aring):
… having a com-
mon axis

23. 23
Gantry bearing
The body [9] is supported in two bearing bushes [10] that are
located next to the grinding wheel on both sides. The spindle be-
arings [6] ensure optimal rotation.
The drive is provided externally via the v-belt pulley [7]. It trans-
fers the rotation to the inserted torsion bar [8] that drives the
spindle itself. Such a drive is referred to as free of lateral forces.
Forces as they arise during tensioning of belts thus do not act on
the spindle bearings.
If a wheel mount [2] is used, it is pushed with the mounted wheel
onto the spindle. The spindle nut [5] fixes the wheel support by a
means of a pressure ring [4] and the clamping cone [3] (Fig. 2-4).
[1] Wheel
[2] Wheel mount
[3] Clamping cone
[4] Pressure ring
[5] Spindle nut
[6] Spindle bearings
[7] V-belt pulley
[8] Torsion bar
[9] Body
[10] Bearing bushes
Fig. 2-4
Gantry bearing
Spindles | 2 Machine concepts

24. 24
More rigid than floating bearing
Suitable for large grinding widths
Wheels can be mounted on the spindle directly and without a
wheel mount
Time-consuming wheel change
Floating bearing
The shaft [2] is supported only in one bearing bush [6] at several
points. The spindle bearings [7] ensure optimal rotation.
The drive is provided via the v-belt pulley [8]. It transfers the rota-
tion directly to the spindle. A disadvantage of this type of power
application is that tension forces from the belt act directly on the
rear spindle bearing.
Fig. 2-5
Floating bearing
[1] Wheel
[2] Shaft
[3] Wheel mount
[4] Clamping cone
[5] Spindle nut
[6] Bearing bush
[7] Spindle bearings
[8] V-belt pulley
2 Machine concepts | Spindles

25. 25
If a wheel mount [3] is used, it is pushed with the mounted wheel
[1] onto the spindle. The spindle nut [5] and the clamping cone
[4] fix the wheel mount (Fig. 2-5).
Quick wheel change
Unsuitable for large grinding widths
Always requires an additional wheel mount
Lower rigidity
The regulating wheel runs usually in gantry bearings for reasons of
stability. If it is provided with a floating bearing, it often receives
an additional support bearing.
2.3.2 Wheel mounting
The grinding or regulating wheel is either mounted directly on the
spindle (direct mounting) or fixed previously on a so-called wheel
mount (Figs. 2-4 and 2-5).
If multiple wheel sets are used in a machine, the use of wheel
mounts is preferable. This does not require replacing each wheel
individually, but only the wheel mount is replaced instead. The setup
times for changing a workpiece type can thus be reduced. A floating
spindle bearing always requires a wheel mount.
2.3.3 Spindle bearings
Both rolling bearings and plain bearings are used as spindle bea-
rings. Some bearing types are more and others less suitable, de-
pending on the application and cost. The table below gives a brief
overview of the types of bearings:
Spindles | 2 Machine concepts

26. 26
Rolling bearings Plain bearings
Hydrodynamic
bearings
Hydrostatic bearings
Cost-effective, since no
oil generator necessary
Maintenance-free
High speeds possible
Good damping
High rigidity
Wear-free continuous
operation
Maintenance and
wear-free
Very high rigidity and
damping
Must be replaced if
worn
Low damping
Higher price than
rolling bearings
Deficit in the
lower speed range
Note: Regulating
wheel can be used
only from approx. 35
rpm
Very high price
Conclusion: Advantage-
ous at high speeds, more
cost-effective than plain
bearings
Conclusion: Good
price/performance
compromise
Conclusion: Except
for the price, the best
solution
Low noise
Adjustment of the grinding
spindle bearing limits the
usable speed range
Strong heat generation at
higher speeds
Extensive gasket
Maintenance-free
Tab. 2-2
Spindle bearings
2 Machine concepts | Spindles