FIELD OF THE INVENTION

The present invention relates to a taper bush for centering a machine spindle
with respect to a hole of unknown geometrical center in a process of machining
the hole. The invention further relates to a method of machining a hole of
unknown geometrical center by centering the machine spindle using a taper
bush.
BACKGROUND OF THE INVENTION
A steam turbine consists of three main components viz. Outer casing, inner
casing and bladed rotor. Rotor of the turbine is kept in the inner casing and the
inner casing is then covered by the outer casing of the turbine. The outer casing
is divided into two parts i.e. upper and lower outer casing. In order to save time,
the machining wok on both the halves of the outer casing has to be performed
simultaneously on different machines. Joint (threaded) holes for fastening the
upper and lower outer casing together are first made on a joint plane of the
upper half of the outer casing and the threaded holes are then transferred from
the upper half to the lower half of the outer casing.

Sometimes it is required that the hole is made on one machine and then the
boring of the pre drilled hole (to increasing hole dia) is done on the other
machine due to manufacturing plan priorities. Further, locating a hole with
preciseness and drilling being important, it should be performed on high end CNC
machining, and the operation of increasing the diameter after the hole is located,
is done on a simpler manually operated machine for economy purpose.
However, the disadvantage in the said operational sequence is that for a pre
drilled hole, increasing the hole diameter on a manual machine, requires that the
center of the hole is to be perfectly located manually only, failing which the hole
will not be perfectly circular or centric, and there will be a mismatch while
making a threaded joint using that hole after boring.
As per the current practice, the job is loaded on the machine, using clamps and
studs, then its horizontal and leveling positions are set. The pre-Drilled hole for
final boring is set using the dial and the scribe is started. The scribe is placed on
the periphery of the dead center and the dead center is manually rotated slowly
in a way that the scribe is partially inside the pre drilled hole and it is then
visually checked that the point of the scribe is equi-distanced from the edges of
the pre drilled hole.
The overall process is lengthy and solely depends on human expertise, which is
likely to generate operational errors. Therefore it is required to have a new
technological item that can establish a standard method of centering a pre dilled
hole.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a taper bush for centering a
machine spindle with respect to a hole of unknown geometrical center in a
process of machining the hole.
Another object of the invention is to propose a method of machining a hole of
unknown geometrical center by centering the machine spindle using a taper
bush.
A further object of the present invention is to propose a method of machining a
hole of unknown geometrical center by centering the machine spindle using a
taper bush which reduces the operational time and precisely locate the hole
center without error.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows a taper bush according to the invention
Figure 2 shows a schematic illustration of the method of the invention using the
taper bush of figure 1.

DETAIL DESCRIPTION OF THE INVENTION
As shown in figure 1, and in a first aspect of the invention, there is provided a
taper bush for centering spindle with respect to a hold of unknown geometrical
center.
The taper bush is configured with different serrated diameters on its taper profile
in order to match with the pre drilled hole.
There is a recessed hole at the center of the outer diameter of the bush so as to
locate the center of the bush.
In a second aspect of the invention, there is provided a method of machining a
hole of unknown geometrical center by centering the machine spindle using a
taper bush.
There is a recessed hole at the center of the outer dia of the bush as to locate
the center of the bush.
The methodology of using this bush so as to locate the spindle to the center of
the pre drilled hole is as under:

1) Put the bush in pre drilled hole manually.
2) Bring spindle close to the outer dia of the bush
3) Place the machine dead center on the recessed hole (which is at the center of
the bush).
4) After placing the dead center, push the spindle towards the hole.
5) If the bush is not at the center, it will tend to move/tilt on either side of the
hole as per the resultant force generated by push of the spindle.
6) Adjust the spindle location as per visual inspection such that bush is inside the
hole equidistantly from all sides. Check for equidistance using the serrated
diameters provide on the taper profile of the bush.
The bush will go inside the taper hole upto a certain diameter equaling the hole
dia. At this point, the spindle will be automatically at the center of the hole since
the dead center was placed at the center of the outer dia of tapered bush.

WE CLAIM :
1. A taper bush for centering spindle with respect to a hole of unknown
geometrical center consisting of a taper bush having different serrated
diameters on its taper profile in order to match with pre drilled hole and a
recessed hole at the center of the outer dia of the bush as to locate the
center of the bush and,
a method of machining a hole of unknown geometrical center by centering the
machine spindle using a taper bush, the taper bush comprising a plurality of
serrated diameters on the taper profile to match with the pre-drilled hole, and a
recessed hole at the center of the outer diameter of the bush, the method
comprising the steps of:
placing the bush in the pre drilled hole manually;
shifting the machine spindle close to the outer diameter of the bush;
placing the machine dead center on the recessed hole of the taper bush;
pushing the spindle towards the pre-drilled hole;
determining whether or not the bush is at the center based on the
tendency of the bush to move/tilt on either side of the upon pushing of
the spindle; and

adjusting the spindle location such that the bush is inside the hole
equidistantly from all sides the equidistant location being checked using
the serrated diameters provided on the taper profile of the bush.
2. A taper bush for centering spindle with respect to a hole of unknown geometrical
center as claimed in claim 1 in which different serrated diameters on its taper
profile are provided for referring and ensuring complete insertion of the bush in
the pre drilled hole.
3. .A taper bush for centering spindle with respect to a hole of unknown
geometrical center as claimed in claim 1 in which the recessed hole at the center
of the outer diameter is used to support dead center attached to the spindle of
the machine.
4. A taper bush for centering spindle with respect to a hole of unknown geometrical
center as claimed in claim 1 is a technological item.