FIELD OF INVENTION
The present invention relates to an improved process for making threaded holes
in field lead core bars for a generator shaft operated in a horizontal boring
machine. The present invention relates to an improved tool device to carry out
the process of the invention.
BACKGROUND OF THE INVENTION
Generally two types of rotor shaft are manufactured. In the first case, current
from the exciter to the poles of a generator rotor is transmitted through a slip
ring. The second type is brushless exciter, in which current carrying path is
configured within the rotor and current from the exciter shaft is transmitted to
generator rotor through a pin on the coupling face of the generator rotor, (as
shown in fig.1)
Current carrying bolts and field lead core bars are made of copper. These
components are fitted in the exciter and the generator shaft for transfer of
current from the exciter to a plurality of electro-magnetic poles of the generator
rotor through pins on its coupling face.
Core bars are generally made in two semi-circular halves. First of all, a flat
portion and ends of the core bar are machined. After this, 12 mm thick insulation
sheet is put between two halves and then the two halves are clamped together
with the help of a plurality of technological clamping rings at both the ends.

Thereafter, the diameter of these assembled core bars halves are machined as
per drawing requirement. Location of holes are transferred from the rotor to the
core bar before separating the two halves for drilling and taping operation.
Drilling and threading operations on those curved surface of the core bar as per
marking are carried out on a horizontal boring machine.
The problems experienced in making a threaded hole of M60 X 2 up to a depth
of 60 mm in the core bar of THRI design shaft on a horizontal boring machine
are highlighted in the following steps:
a) drilling a hole dp 58 mm up to a depth of 60 mm.
b) a taper at bottom of the hole being left due to the pointed shape of the
drill, is then flattened by a flat drill.
c) Firstly for cutting the threads on the machine, a first tap is used and this
is followed by a fine and accurate thread cutting using a final tap including
a tapping attachment (shown in fig.2). Drilling with a Φ 58 mm drill
mostly causes holes of size more than dp 58 mm (i.e. 58.20 mm to 58.40
mm).
Because of the reason oversize holes being generated in most of the cases of
prior art, "NOT GO GAUGE" is found passing after the final tapping. During the
tapping operation, chips get struck between the tap and threads and while
making the tap reverse, these chips damage the threads. The reason is that the
core bars are made of copper which is very soft material.
Thus, the generated holes with damage threads are rectified by enlarging these
holes to bigger size of M90 X 2 through out the thickness of the core bar. Then,
a threaded plug of copper of OD 90 is fitted in it. This plug is then locked by
caulking. After caulking the plug, it is brazed with the core bar using silver
brazing alloy for making it an integral part of the core bar. Then, the threaded

holes of size M60 X 2 are again made by same process. To overcome these
problems, an improved process for making threaded holes in field lead core bars
for a generator shaft including an improved tool device to carry-out the process
is considered essential.
A thorough analysis of prior art disadvantages reveals that the basic problems
reside in:
a) Copper material of field lead core bar being very soft, cutting edges of the
tap dig inside it due to the pressure generated during cutting and reverse
tap movement. Thus, material composition and construction causes over-
sized holes and broken threads.
b) Chips stuck between the tap and threads damage the threads, which is
not acceptable from the quality control parameters.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose an improved
process for making threaded holes in field lead core bars of a generator shaft
which eliminates the disadvantages of existing state of art.
Another object of the present invention is to propose an improved process for
making threaded holes in field lead core bars of a generator shaft which reduces
the percentage of defects.
A further object of the present invention is to propose an improved process for
making threaded holes in field lead core bars of a generator shaft which reduces
the high degree of rectification works.

A still further object of the present invention is to propose an improved process
for making threaded holes in field lead core bars of a generator shaft which
reduces time and cost.
An yet further object of the present invention is to propose an improved tool
device for making threaded holes in field lead core bars of generator shaft which
is capable of implementing the process of the invention.
SUMMARY OF THE INVENTION
At least two cylindrical shape boring bars having diameter in the range of 18mm
to 60mm and length in the range 40mm to 200mm for threading operation of
holes M36 to M125 on horizontal boring machine are designed and configured.
One of the boring bars shall be suitable for holding a threaded tool and for
making grooves at 90° angle at the bottom of the holes. The second boring bar
is adaptable to hold the tool at 45° angle for boring holes so as to generate a
90°C corner at the bottom of the blind hole.
The thread profile cutting tools and grooving tools are ground on forwarded side
of the tool-bit for generating threads as per drawing (as shown in fig.3).
The core bar is provided with a groove of 2.5 mm width X dia 61 mm at the
bottom of the hole to facilitate threading operations up to the full threaded
length.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Fig-1 shows a photo figure of a Field lead core bar with current carrying bolt

Fig-2 shows a photo figure of a Taping Attachment with the machine tap as
per prior art
Fig-3 shows a photo figure of a Boring bar dp 30 including the small tools as
per the invention
Fig-4 shows a photo figure of the Field lead core bar after machining the hole
Fig-5 shows a photo figure of the tool device according to the invention
Fig-6 shows a schematic view of operational details of the tool device
Fig-7 shows a photo view of a boring operation for a Φ 60 mm with the tool
device of the invention
Fig-8 shows a photo view of M60 X 2 threading operation on the field lead core
bar with the tool device of the invention
Fig-9 shows a photo view of M85 X 2 threading operation being generated in
Exciter shaft 500 MW with a hole up to depth 172 mm in Brass material
and rest of the depth of 98 mm being in steel
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
As shown in figs. 5&6, detailed process for making threaded holes using new
tools attachment with the tool device and for making threads from M36 to M125
on horizontal boring machine in components made of non ferrous and ferrous

material. The process of making one of such threaded holes M60 X 2 is
elaborately described below:
(1) Core bar halves are clamped in vertical position supported on an angle
plate on rotary table of horizontal boring machine (fig-1 & fig-7)
(2) hole Φ 56 mm is drilled up to the depth of 60 mm
(3) bottom of the hole is flattened with Φ 56.5 mm flat drill
(4) the hole Φ 56.5 mm is enlarged to size Φ 58.10 mm by using developed
micro boring lead (3) (fig.6A)
(5) groove size 2.5 mm X dia 61 mm is made at the bottom with the help of
specially developed grooving tool (fig.6B)
(6) Finally threads of M60 X 2 are cut with the help of the threading tool (5)
(fig.6C)
(7) Finally threaded holes are checked with a thread plug gauge to ensure
the quality of the threads
Time taken to complete the core bar is only 4 hours and more number of field
lead defect free core bars can be produced.
Total Savings
Lot of saving of manpower, machine time, cycle time and material due to
development of this innovative process which in turn reduced production cost.
Also the engagement of over head crane and handling shaft which is very critical
resources reduced due to this innovation and possibilities of mechanical damage
to the components are reduced.

WE CLAIM
1. An improved process for making threaded holes in a horizontal boring
machine on the core bar halves, comprising the steps of:
- affixing the core bar halves in vertical position on a rotary table of the
horizontal boring machine;
- drilling a hole in a right position;
- flattening the bottom of the hole with a boring tool (3);
- enlarging the bore of the hole by a boring tool (3)
- making a grove 2.5-3.0 mm size at the bottom of the hole with a grooving
tool (4); and
- finally cutting the thread with a threading tool (5).

2. The process as claimed in claim 1, wherein flattening the bottom of the
hole and enlarging the bore hole are machined by a boring tool (3) having
an access to 45° angle.
3. The process as claimed in claim 1, wherein said groove is machined by a
groove tool (4) having enabled to operate at least at 90° angle.
4. The process as claimed in claim 1, wherein the threads are machined in
the hole by a threading tool (5).
5. An improved tool device for implementing the process as clamed in claim
1, comprising at least two cylindrical holding bars (1,2), a boring tool (3)
capable to access on the job at an angle of 45°, a groove tool (4) enabled
to operate at 90° angle, and a threading tool (5) to machine the threads.
6. The tool device as claimed in claim 5, wherein said tools (3,4,5) are
mountable at one end of at least two cylindrical holding bars (1,2).

7. The tool device as claimed in claim 5, wherein said cylindrical holder bars
(1,2) having 18mm to 60 diameter and 40 mm to 200 mm length for
making threaded holes in M36 to M125 on horizontal boring machine.
8. The tool device as claimed in claims 5 to 7, wherein the tips of the tools
(3,4,5) are made of steel material.
9. The tool device as claimed in claim 5 to 8, wherein both steel and non-
ferrous materials can be machined.

At least two cylindrical shape boring bars having diameter in the range of 18mm
to 60mm and length in the range 40mm to 200mm for threading operation of
holes M36 to M125 on horizontal boring machine are designed and configured.
One of the boring bars shall be suitable for holding a threaded tool and for
making grooves at 90° angle at the bottom of the holes. The second boring bar
is adaptable to hold the tool at 45° angle for boring holes so as to generate a
90°C corner at the bottom of the blind hole.
The thread profile cutting tools and grooving tools are ground on forwarded side
of the tool-bit for generating threads as per drawing (as shown in fig.3).
The core bar is provided with a groove of 2.5 mm width X dia 61 mm at the
bottom of the hole to facilitate threading operations up to the full threaded
length.