FIELD OF INVENTION:
The invention generally relates to manufacture of turbo generators and in
particular to a special drilling jig for drilling holes for transfer of current from
field exciter to rotor poles.
BACKGROUND OF THE INVENTION
Slip ring shaft is mounted on the generator rotor at the exciter end. Current
from exciter is transmitted to rotor poles through current carrying bolt holes in
the slip ring shaft. Current carrying bolt and field lead core bar made of copper
are the components fitted in the slip ring shaft for transfer of current. But
transfer of holes from slip ring to field lead core bar is a typical operation.
Earlier attempts were made through using Bush (1) & Pin (2) shown at Page-7.
Pin of ? 65 was fitted in hole of Slip Ring Shaft at ? 65 (see page 1 & 2). This
Pin was to used to align machine spindle with the hole, after alignment pin was
removed & bush was fitted at the same place. Then ? 28 hole was done on
Field Lead Core Bar through bush.
Limitation of old method was that due to non availability of positive locking in
Bush & Pin, these used to move or shift during process and thereby causing
the shift in hole location on Field Lead Core Bar.
The limitation of the earlier method has been successfully addressed through
this invention. The typical operation of hole transfer from current carrying bolt
holes in the slip ring shaft to holes on field lead core bar can only be done with
the help of the invented jig, to avoid mismatch of holes. Such typical operation
which is very vital in the overall manufacturing schedule, suffered due to non
availability of a suitable drilling jig and resulted in repeated rejection of field
lead core bar due to mismatch of the current carrying bolt holes and holes of
the field lead core bar.
In case of mismatching, holes are enlarged and plugged with threaded copper
plug and sent to the machine shop again and again resulting in hold up of the
production schedule which again lead to overall delay in delivery time. The
problem of mismatching of holes between current carrying bolt holes with the
holes of field lead core bar in the slip ring shaft has been successfully
addressed through the special drilling jig, the subject of present invention.
OBJECTS OF THE INVENTION
An object of the invention is to provide a drilling jig to prevent mismatching of
holes between current carrying bolt holes and holes in field lead core bar for
smooth transfer of current from exciter to rotor poles.
Another object of the invention is to minimize production down time on
account of such mismatching errors, affecting manufacturing schedule and
quality of the product.
Still another object is to eliminate repeated rework costing time and money and
adding to infructuous labour costs.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: Shows the slip ring shaft
Figure 2: Section B - B of the slip ring shaft.
Figure 3 & 4: Show the sectional view of the slip ring assembly.
Figure 5: Shows the sketch of special type drilling jig with alignment plug.
Figure 6 (i, ii, iii): Shows the special bushes being used with special type
drilling jig with alignment plug.
Figure 7: Shows the sketches of bush for hole transfer (item no. 1) and pin for
alignment (item no. 2) used in the old process.

DESCRIPTION OF THE INVENTION
The invention will now be described in an exemplary embodiment as depicted
in the accompanying drawings. There can however be other embodiments of
the same invention, all of which are deemed covered by this description.
Slip ring shaft (1) figure(l) is mounted on the generator rotor at the exciter end
and current from exciter to rotor poles is transmitted through current carrying
bolt (8) of figure (3) fitted in the slip ring shaft and holes in field lead core bar
(2) inserted in the axial hole of the slip ring shaft. Field lead core bar is a
cylindrical insulated component made of two semicircular copper conductors
separated from each other with 10 mm thick insulation sheet.
Figures 3 8s 4 show the sectional view of the slip ring assembly.
Figure 5 shows the invented jig (3), with alignment plug (A). The part of jig
marked (A), called alignment plug, forming the outer diameter of the jig, is used
to align the machine spindle of the boring machine and portion marked (C)
forming an annular hole in the inner diameter of the jig and the bush (E)
integral to the jig, houses three no. external bushes which are fitted one after
another as shown in (Figure 6 i, ii, iii).

The jig is suitably threaded at (B) so that it fits in the current carrying bolt hole
(8) on the slip ring shaft (1). The portion marked (E) of the jig is a bush integral
to the jig which fits into the hole of the slip ring shaft through threading (B).
The threading (B), (X) and (E) - of invented jig (Figure 5) diameter of the bolt
hole are within close tolerance so that to it ensures positive locking of the bolt
hole and the jig. It does not allow the invented jig to shift during drilling
process. The jig on being fitted on to the bolt holes on the slip ring shaft rest on
the shaft on the collar of the jig marked (X). Three bushes of different
dimensions (4, 5, 6) are fitted in the inner diameter of the jig for guiding the
drilling tool one after another and are locked by a locking screw (D).
Three no bushes (4, 5, 6) which are shown in Figure (6 i, ii, iii) are fitted one
after another as already mentioned. The drill, core drill and reamer passes
through the respective bushes as shown Figure 6 for transfer of hole on the
field core bar which is inserted in the slip ring shaft. The bushes are replaced
after unlocking the screw (D).

WE CLAIM;
1. A drilling jig (3), comprising an alignment plug (A) with inner diameter (C)
a bush (E), collar (X), a threaded part (B), a locking screw (D) having
three external bushes (4), (5) and (6) capable of being fitted in the inner
diameter (C) for guiding drilling tool, the threaded part (B) being fitted in
the bolt hole of the slip ring shaft characterized in that the threaded part
(B) is made within close tolerance of the diameter of the bolt hole (8) so
that there is positive locking between the bolt hole and the jig, which
does not allow shifting of the invented jig during drilling, preventing
mismatching of hole.
2. The jig as claimed in claim 1 wherein alignment plug (A) is formed on the
outer diameter, another hole in the inside diameter (C) runs across the
length of the jig, threaded portion (B) is made on the outer diameter of
the jig, bush (E) fits into the hole of the slip ring shaft and the entire jig
sits on the slip ring shaft on collar (X).
3. The jig as claimed in claim 1 wherein three external bushes (4, 5, 6) are
housed in the inner diameter of the bush.
4. The bushes as claimed in claim 3 are of different dimension, replaceable
and locked by a locking screw (D).
5. A method comprising steps of:
a) inserting field lead core bar (2) inside the slip ring shaft (1),
b) fixing the drilling jig (3) on the current carrying bolt (8) hole of the
slip ring shaft (1),
c) positioning the slip ring shaft in required position with the help of
alignment plug inserted in the current carrying bolt hole of the slip
ring shaft,
d) fixing three bushes (4,5,6) inside the jig successively,
e) drilling, core drilling and reaming in one half of the core bar and
locking the position by a locking pin fitted through slip ring shaft,
f) rotating the slip ring shaft as per requirement to align next hole
and repeating the process as in (b), (c) and (d) for drilling, core
drilling and reaming, in next three holes as shown in Figure 2 and
g) taking out the field lead core bar inserted in the slip ring shaft.
6. The method as claimed in claim 5 wherein the bushes are fitted one after
another by replacing them in an ordered sequence for drilling, core
drilling and reaming operation.

A drilling jig with alignment plug (A) to avoid mismatch of holes between
current carrying bolt holes on the slip ring shaft and the field lead core bar
inserted inside shaft for transmission of current from exciter to rotor poles.
The part of the jig (A) called alignment plug (A) forming outer diameter of the jig
is used to align the machine spindle of the boring machine and portion marked
(C) forming an annular hole in the inner diameter of the jig are integral to the
jig, houses three numbers external bushes (4, 5, 6) which are fitted one after
another for carrying out drilling, core drilling and reaming operation by the
boring machine. The jig is suitably threaded at (B) so that it fits into the
current carrying bolt hole (8) on the slip ring shaft (1). The portion marked (E)
of the jig is a bush integral to the jig which fits into bolt hole of the shaft. The
replaceable bushes (4, 5, 6) are fitted with a locking screw (D). The threading
(B) and diameter of the bolt hole are within close tolerance so that it ensures
positive locking and does not allow the bush (E) to shift while drilling matching
hole in the field lead core bar, thus ruling out the possibilities of mismatch.