FIELD OF THE INVENTION
The present invention in general relates to the field of large size electrodynamic
machines having a cylindrical-core rotor-member carrying a field winding, and
a cylindrical-bore stator-member. More particularly, the invention related to an
improved device and method for simultaneously and accurately machining
finger bars for a stator core corresponding to large size synchronous motors.
BACKGROUND OF THE INVENTION
Background description includes information that may be helpful in
understanding the present subject matter
The stator core of a large size synchronous motor is build up in layers using
thin iron sheets stampings made of thin iron sheet. These thin stampings are
placed side by side and also stacked layer above layer to form a monolithic
mass known as Motor core. This process of stacking and compressing thin
lamination is done to minimize eddy current losses in a motor. Such a hollow
cylindrical stator core is placed inside the stator outer frame. For executing the
correct electromagnetic and mechanical functionalities, the inner diameter of
the stator is maintained by fixing the position of stampings with respect to the
stator body. Therefore, the inner diameter as well as location of these
stampings with respect to each other is very critical to design. Slot tooth are
provided to form slots for winding bars. These slot teeth are weakest part of
core 1 and also have to bear maximum forces due to exposure to high magnetic
flux, attributed to it closeness to rotor pole. Slot teeth being the weakest and
also exposed to highest forces need proper support against any mechanical
damage. Thus machining these finger bars with high accuracy is a prerequisite.
Depending on design, there can be more than 250 such finger bars being used

and dimensional accuracy of each of these finger bars is very critical for
manufacturing of stator core in specific and motor in general.
It was observed that in the higher rating motors, there exists an unbalance
during the balancing of motors. Any misalignment in manufacturing of core
causes eccentricity and the resulting increase in vibration shall hamper the
balancing of the motor. This results in enormous amount of rework in core
press ring fingers and time as the motor is required to be taken back to shop
from balancing tunnel to back. So, there exists the need to have high degree
of precision and alignment in fingers for motor core to function as desired.
The fingers bars, generally a prismatic bar, of the core being machined as
individual component in prior art was leading to non-repeatable quality, motor
vibration and balancing issues. Thus, there is a need of a device and method
for simultaneous processing of large size motor finger bar with improved means
capable of setting, clamping and machining of the core press ring fingers to
achieve high level of motor built up quality.
OBJECT OF THE INVENTION
It is therefore primary object of the invention to solve aforementioned problem
by proposing a device for stator motor for better mechanical support to the
slot teeth without hindering the slot exit of the bars.
Yet another object of the invention to propose a method and device for
machining finger bars corresponding to large size synchronous motors having
low initial cost and upkeep, great and continuing accuracy inherent in its
configuration and operation, ruggedness and simplicity in its construction and
operation, consistently reproducing the desired manufacturing.

Still another another object of the invention is to batch process the finger bars
so as to control the quality better with high production rate and with better
ergonomics.
SUMMARY OF THE INVENTION
The present invention is therefore intended to solve one or more of the above
problems by a proposed method and device for simultaneous processing of
large size motor finger bars.
the method comprising steps of: securing a base plate in a T-slot of a machine
bed (M) using a threaded bolt; securing said threaded bolt at suitable length
of shank to first pass through a hole for securing said base plate; parallel
laying a finger bar in sidewise adjacent manner in a slot of said base plate;
placing a clamping unit horizontally over said finger bars to rest over it in
horizontally supported position; passing shank of said threaded bolt through a
hole of the clamping unit to fasten into a threaded hole (24) of said base plate;
tightening the threaded nut over the clamping unit for required clamping force
over the finger bars against any machining force; and, pushing a threaded
means (27) in a hole (26) of said base plate against the already clamped bars
on the top to prevent any rattling movement during machining.
width of the slot is variable depending upon number of said fingers to be
machined at a time and size of the slot to be increased in multiples of the
width.
BRIEF DESCRIPTION OF THE ACCOIMPANYING DRAWINGS
The illustrated embodiments of the subject matter will be best understood by
reference to the drawings, wherein like parts are designated by like numerals
throughout. The following description is intended only by way of example, and

simply illustrates certain selected embodiments of apparatus that are
consistent with the subject matter as claimed herein.
Figure 1 illustrates cross sectional view of a stator core provided with frame
structure.
Figure 2 illustrates details of stamping done in a stator core.
Figure 2,3 illustrates an isometric view of proposed means for simultaneous
processing of large size synchronous motor finger bars with different stages of
bar laying.
Figure 6 illustrates a line representation of the base plate for simultaneous
processing of large size synchronous motor finger bars.
Figure 7 illustrates a line representation of the clamping unit of large size
synchronous motor finger bars.
DETAIL DESCRIPTION OF THE INVENTION
The foregoing and other features of the invention, comprising the improved
device and method for machining finger bars corresponding to large size
synchronous motors with the construction and relative arrangement of the
several parts, will be apparent from the following more particular description
of the invention, as illustrated in the accompanying drawings, in which like
reference characters refer to the same parts throughout the different figures
and subsequently incorporated in the subjoined claims. The drawings are not
necessarily to scale instead emphasized upon illustrating the principles of the
invention.
Referring to figure 1 and 2, number of thin stampings L (up to 15000-20,000
or more depending on core size and motor rating) are stacked over one other
and placed side by side in circular pattern and then compressed to form a

monolithic mass of motor core (1). This process of stacking and compressing
thin lamination to is done to minimize eddy current losses in a motor. The
height of such a motor core can reach over 4 meters in length. The core (1) is
supported on one side, which is the outer periphery, by a stator frame (3) (also
called yoke) and the inner circumference of the core (1) is hanging in the air.
Slot tooth (5) are provided to form slots (4) for insertion of stator winding bars.
These protruding slot teeth (5) are weakest part of core (1) and also have to
bear maximum forces due to exposure to high magnetic flux, attributed to its
closeness to rotor pole. To make the core (1) a monolithic mass, the stamping
L of approx. 0.5 mm thickness (Refer Fig 2) are tightened with long insulated
studs’ S and insulated washer IW passing through the stampings as well as
core press ring R at both the ends. To exert the compression force uniformly,
the core press ring in provided with a number of finger bars so that as to avoid
any damage to the slot teeth 5 upon application of tightening force. Depending
on design, there can be more than 250 such finger bars being used and
dimensional accuracy of each of these finger bars is very critical for
manufacturing of stator core in specific and motor in general.
Referring to figure3 and 4, a base plate (10) is secured in the T-slot of the
machine bed M by uprightly using a threaded means (11,12). The threaded
means (11,12) is threaded at suitable lengths at its shank so as to first passes
through a hole (25) to secure the base plate (10).
Referring to figure 5 (and fig.4), once the base plate (10) is secured in machine
bed using threaded means (11,12), the finger bars (30) can be parallely laid
sidewise adjacent to each other in slot (32) of base plate (10). However, the
width of the slot (32) can be varied depending upon the number of finger (30)
to be simultaneously machined in single setting. Also the width of the slot (32)

in plate (10) should be in close tolerance to the width of at least one slot (32)
and can be increased in multiples of the width of the slot.
After placing the finger bars (30) on the base plate (10), slot (32), the clamping
unit (20) is placed horizontally over finger bars to rest over it. Once the finger
bars (30) are placed on the base plate (10) of slot (32), the clamping unit (20)
is horizontally placed over the said bars such that it rests over the bars. While
the clamping unit (20) achieves this horizontally in simply supported position,
the shank of the threaded means (22) shall pass through the hole (21) of the
clamping unit (20) to fasten into a threaded hole (24) of the base plate (10).
The threaded means (22) is thereupon tightened over the clamping unit (20)
to provide required clamping force on finger bar (30) against the aggressive
machining forces. Upon tightening, a threaded means (27) in hole (26) of base
plate (10) can be threadlike pushed against the already top clamped bars (32)
to arrest any rattling movement during machining.
The number of finger bars (30) in a stack shall depend on the machine’s ability
to machine the stack in one go while meeting the quality of standards. This
may be material removal rate, finished product lead time, strength of the
material used in the proposed device etc.
Additionally, in order to enhance threading strength, it is advisable that the
height of slot (32) should at least be more than 2mm to that of the height of
a single bar (30).

WE CLAIM:
1. A method for simultaneously processing large size turbo generator finger
bar, the method comprising steps of:
- securing a base plate in a T-slot of a machine bed (M) using a threaded bolt;
- securing said threaded bolt at suitable length of shank to first pass through
a hole (25) for securing said base plate;
- parallel laying a finger bar (30) in sidewise adjacent manner in a slot (32) of
said base plate;
- placing a clamping unit horizontally over said finger bars to rest over it in
horizontally supported position;
- passing shank of said threaded bolt through a hole (21) of the clamping unit
to fasten into a threaded hole (24) of said base plate;
- tightening the threaded nut over the clamping unit for required clamping
force over the finger bars against any machining force; and,
- pushing a threaded means (27) in a hole (26) of said base plate against the
already top clamped bars (32).

2. The method as claimed in claim 1 wherein, pushing the threaded means
(27) in the hole (26) of said base plate against the already top clamped bars
(32) to prevent any rattling movement during machining.
3. The method as claimed in claim 1 wherein, width of the slot is variable
depending upon number of said fingers to be machined at a time.
4. The method as claimed in claim 1 wherein, size of the slot to be increased
in multiples of the width.

5. A device for simultaneously processing large size turbo generator finger bar
comprises of a base plate (10), a threaded bolt (11, 12), a finger bar (30),
a clamping unit (20) and a threaded means (22).