FIELD OF INVENTION
This invention relates to a spherical contour machining attachment for lathe to generate
spherical surface on turbo generator shafts. More particularly, the invention relates to a
spherical turning attachment and a method of turning for producing a smooth spherical
surface of high surface finish.
BACKGROUND OF THE INVENTION AND PRIOR ART
Turbo generators of 235 to 250 MW have long and heavy forged shafts. Turning,
facing, grooving, threading and contour machining operations are carried out on lathe
over these shafts. Due to heavy weight, babbitt lined, steady is used for both at chuck
end and tail stock end for support. Motion to the shaft is transferred through universal
shaft which is attached to the machine on check end. Before generating spherical
surface on the shaft, a cylindrical surface of the required dimensions is produced. For
producing spherical surface a group of more than two tools is ground such that it
produces required contour. For machining of spherical surfaces on these generator
shafts, the tool contour is ground to match the spherical surface. A series of three
number of tools with different contours are required to complete full spherical surface.
Feed of the tool is regulated manually. The operator manually operates the tool feed

that requires constant vigil for the operation, cross feed of the tool is kept very small for
generating high surface finish as per requirement.
Fan blades are mounted on these spherical surfaces for creating forced air circulation
inside the generators for cooling of rotor coils.
Due to machining in stages with a combination of tools, steps are observed on the
spherical surface. These steps are removed with the help of emery paper. It consumes
extra hours to rectify the surface. When step marks are prominent hand grinder is used
to rectify the surface. This is done manually on a running machine involving high risk
for operator, job and equipment. Quality of the surface finish, even after these
rectification works, is not satisfactory and need extra efforts to improve. The process is
very slow and reliability is also low and also very tiresome for operators. Productivity
always suffered.
Hence, there exists a need to provide a spherical attachment which can eliminate the
disadvantages of prior art.
OBJECTS OF THE INVENTION
Therefore it is an object of the invention to propose a spherical contour machining
attachment for lathe to generate spherical surface on turbo generator shafts which is
capable of producing a smooth spherical surface with high surface finish.

Another object of the invention is to propose a spherical contour machining attachment
for lathe to generate spherical surface on turbo generator shafts which is capable of
improving the productivity.
A further object of the invention is to propose a spherical contour machining
attachment for lathe to generate spherical surface on turbo generator shafts which has
an economical significance.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 - shows a line diagram of a front view of spherical contour machining attachment
Fig.2 - shows a line diagram of a top view of a spherical contour machining attachment
Fig.3a - shows spherical setting on lathe machine and
Fig.3b - shows required spherical contour on the shaft
Fig.3c - shows the contour (C) after cutting and shape (D) before cutting
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
A spherical contour machining device (S) which can produce spherical surface (C) with
varying diameter keeping in view future requirement of generators of 660 MW and

above. The device consists of a tool post (5) and a cutting tool (6), a base plate (4), a
connecting rod (3), a support plate, a link rod, a pivot pin and a bush assy (1), a feed
dial (2). The base plate (4) is like a cross beam with the rest on bed of the machine.
Front portion of the base plate has one ground plate bolted on it which acts as slide for
the tool post. Rear end of the base plate has another plate which holds hinge for link
rod connected with tool post. One end of the link rod is hinged on rear end plate with
pin and other end is connected with the tool post. A collar pin of 60 mm outer dia is
fixed in the rear end plate and a inner dia 60 mm bush is fitted in the link rod to form a
pivot pin assy (1). The link rod is fitted in the pin and locked with a chuck nut when this
pin acts as centre point for movement of the tool post. Bush and pin are made of hard
metal to avoid wear and tear. The connecting rod (3) is a square section whose one
end is hinged with the tool post and the other end is hinged on the carriage of the
machine with suitable pins. Function of this connecting rod (3) is to give automatic feed
to the tool through carriage of the machine.
Advantages of the new method over the old method
1) The new method has accelerated production of spherical surface on generator
shafts
2) After implementation of the method, 60% of the time is saved for production of
other components on lathe machine.
3) Device is capable of generating higher diameter spherical surface making this
device suitable for higher rating sets.
4) The device and the method are safe for operator and equipment both.

5) With this device time consuming rectification works are avoided compared to old
method.
6) Unlike the old method, the device is capable of generating higher diameter
spherical surface.
7) A good quality of surface is produced.
8) Vibrating and chattering marks on the job are avoided.
9) Device works with automatic feed compared to manual feed of earlier method
10) In earlier method it took 37 hrs to complete machining operation while with the
introduction of the device it takes only 14 hrs. An increase in production by 60%.

Annual saving 18 x 32844 = Rs. 591192.00 recurring
Hence, Financial Saving = Rs. 5.92 lacs per year,
The process essential to generate spherical contour consists of setting the center
line of hinge of link rod coinciding with the axis of shaft. A marking on the
cylinder surface of the shaft is done with the center punch as reference given in
the drawing. This reference point is 80 mm from one end. At a distance of 20
mm on either side of the reference line (XX) two points A and B are marked to
check the setting of the device. A feed dial (2) is mounted on the tool post of the
device and the knob is set on the reference point with needle indicating zero
reading. Deflection of the dial is checked by moving the tool post up to 20 mm
(A and B) mark position on left and right side of the reference point. A turning
tool (6) of size 40x40 mm is mounted on the tool post (5). The carriage of the
machine is longitudinally moved in such a way that tool tip faces 'B' side of the
cylindrical surface on which spherical contour (C) is to be cut. Tool post (5) is
moved forward till the tool tip touches the highest portion of the side '0B'. The
tool post (5) is moved forward to give depth of cut to produce the spherical
surface. Same process is adopted in side 'A' till we get the required spherical
contour surface (C).

WE CLAIM
1. A spherical contour machining attachment for lathe to generate spherical
surface comprising:
a tool post (5) and a cutting tool (6) mounted on it for producing spherical
contour surface;
a base plate (4) disposed as a cross beam on bed of machine;
a ground plate bolted to the base plate (4) acting as a slide for the tool
post;
a plate on the rear end of the base plate (4) for holding hinge for link rod
connected with tool post (5);
a link rod having its one end hinged on rear end plate with pin and other
end connected with the tool post (5);
a collar pin fixed in the rear end plate;
characterized in that a bush is fitted in the link rod and the said link rod is
being fitted in the pin and locked with a chuck nut wherein the pin acts as
centre point for movement of the tool post and a square section
connecting rod (3) having one end hinged with the tool post with a pin
and the other end being hinged on the carriage of the machine with a pin
provides automatic feed to the tool (6) through carriage of the machine.

2. A spherical contour machining attachment as claimed in claim 1, wherein
the outer dia of the pin and inside dia of the bush are 60 mm deployed for
making the pivot pin assembly (1).
3. A method for producing the spherical surface with spherical contour
attachment on turbo generator shafts comprising;
setting the center line of hinge of link rod coinciding with the axis of the
shaft;
marking on the cylindrical surface of the shaft with centre punch as
reference (XX);
marking two points (A and B) at equal distance of either side of reference
line (XX) to check setting of the device;
mounting a dial on the tool post (5) of the device (S) and setting the knob
on the reference point with needle indicating zero reading;
checking the lifting of the dial (2) by moving the tool post (5) up to
marked positions (A and B) on left and right side of the reference point
(XX);
mounting the turning tool (6) on the tool post (5);
characterised in that
the carriage of the machine is longitudinally moved in such a way that tool
tip faces 'B' side of the cylindrical surface and moves forward to touch the
highest portion of the side 'B' and then moves further forward to give

depth of cut to produce the spherical surface and repeating the same
process in other side 'A' to produce the spherical contour surface of the
shaft.
4. A method as claimed in claim 3, wherein the reference line (XX) is 80 mm
from one end.
5. A method as claimed in claim 3 and 4, wherein the two points (A and B)
marked on either side of the reference line (XX) are at a distance of 20
mms each from the reference line.

A spherical contour machining attachment for lathe to generate spherical surface
consists of a tool post (5), a base plate (4) and a ground plate bolted to the base plate
acts as a slide for the tool post (5). A link rod having its one end hinged on rear end
plate with pin and other end connected with the tool post (5). The link rod is fitted with
a pin and bush assy (1) and locked with a chuck nut. The pin acts as center point for
movement of the tool post. A square section connecting rod having one end is hinged
on the carriage of the machine with a pin provides automatic feed to the tool (6)
through carriage of the machine.