FIELD OF INVENTION
The invention relates to an apparatus for marking drill hole locations on the curved
surfaces. More particularly it relates to an apparatus for marking Cartesian co-ordinate
locations on curved surfaces at dished ends of boiler drums and pressure vessels
using polar co-ordinates and a method of doing the same using the apparatus.
BACKGROUND OF THE INVENTION
Boiler drum and pressure vessels have cylindrical shells, which are covered by dished
ends at the ends. The dished ends have curved surfaces which are typically of
Hemispherical or Torri-spherical or ellipsoidal contours in cross section. The dished
ends have openings on them which are used for sampling or fluid flow. The apex of
the dished ends have manhole door opening. In manufacture of the dished end with
openings, the production drawing issued to the shop floor have locations mentioned in
Cartesian coordinates projected on the top view of the dished ends, with axes
meeting points coinciding with the centre of the apex of the dished ends, as per
sketch -1.
The origin of the Cartesian co-ordinates in the drawing also are the centre of the
manhole door opening. The present popular method of marking includes.
■ Using a trammel. Trammel is a device that has two pins parallel to each other
and perpendicular to a common rail. The height of the pins can be

so adjusted, that the two pins are at different heights and the rail is horizontal.
This ensures a horizontal water-level railing and two pins which are at different
elevations and maintain a set distance between each other. This is used to
transfer a linear distance on irregular surface where one point and the other
are at different elevations. One of the trammel pin is kept centered on the apex
of the dished end and the other is used to mark any particular linear distance
from the apex point (The X distance), considered origin of Cartesian axis. The
second point after marking one axis distance, is marked by placing the trammel
on the first point which lies on a sliding profile and keeping two reference
points for ensuring horizontal positioning of the rail. The rail has to be
perpendicular to the first point axis. The point to be marked is arrived by
intersecting the second point marking arc (The Y distance) to the arc measured
for diagonal of the X and Y distances. The surfaces of the marked dished ends
have to be applied with a coating that makes the arcs visible. Tyically used in
shopfloors are quicklime solution, which has to be applied and left to dry.
The other popular method observed was to mark the layout of the Cartesian
coordinates on the floor, an area identified for the purpose and which is clean
and flat. The dished end is inverted and placed such that the apex of the
dished end is on the origin of the coordinate axes. The points lying on the
layout are then transferred to the surface of the dished end. Then the dished
end is positioned back to the position with the large base on the bottom and
the apex on the top. This position enables drilling.
The third popular method observed was to use a costly CNC machine with
absolute X,Y,Z positioning and to mark the dished end for the drill holes.

OBJECTS OF THE INVENTION
It is therefore the object of the invention is to propose an apparatus for marking drill
hole locations on curved surfaces and a method thereof which ensures improved
marking methodology or simplified marking process.
Another object of the invention is to propose an apparatus for marking drill hole
locations on curved surfaces and a method thereof which reduces the cycle time of
operation.
A further object of the invention is to propose an apparatus for marking drill hole
locations on curved surfaces and a method thereof which reduces the material
handling.
SUMMARY OF THE INVENTION
The Cartesian coordinate dimensions in the drawing are as shown in the Fig.-l. The
centre circle is the opening for manhole door. Presently the points are marked on the
dished ends using prior art methods described in the background. The marking using
Cartesian coordinates as per the popular method referred earlier in this document are
more expensive and time consuming.
An apparatus was developed which supported by an in house developed software that
converts the input Cartesian co-ordinates to output polar coordinates, uses the polar
co-ordinates to mark on the surfaces of the dished ends. The apparatus put up for
Patent can locate the points on the dished ends with hemispherical, semi-ellipsoidal
cross section using polar co-ordinates.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - Shows a typical Cartesian coordinate dimensioning on the projected surface of
the dished end as viewed from top, with the origin point in the
coordinate system being the apex of the dished end.
Fig.2 - Shows location of the same points in polar coordinates.
Fig.3 - Shows the apparatus developed for marking using polar coordinates.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT
INVENTION
The present manufacturing drawing gives the drill holes that form the openings on the
dished ends of Boiler / pressure vessel or a heat exchanger as Cartesian coordinate
points. The points are given in a Cartesian coordinate system on the projected surface
of the dished ends. A typical such, dimensioning is as shown in Fig.-l. With reference
to the Fig.-l, the centre circle is the opening for manhole door. The details given as
vl, v2, v3....etc are the details of the different sized openings. The intersection of the
coordinate axes to the point denoted 'II' is the positive X direction and its opposite,
the intersection point to the point marked 'IV is negative X direction. The same
applies to Y axis, the positive direction being from intersection point to point marked
'I' and negative direction is from the point of intersection of coordinate axes to the
point marked 'III'. So the detail in the above drawing having two points detailed as
v5, one on the top quadrant and the other below, shall be fed as having coordinates,
(X,Y) and (X,-Y) respectively. All the points so covered shall have the individual

coordinates fed into the software and the output shall be in polar coordinates, (n the
case of (X,Y) & (X,-Y), they shall be (Radiusl, Anglel) and (Radius2, Angle2)
respectively). The apparatus can mark the polar coordinates on the surface of the
dished ends.
The apparatus is supported by an in-house developed software that converts the input
Cartesian coordinates to output Polar coordinates. The Cartesian coordinates are fed
into the software along with the details of the openings. The software converts the
coordinates into polar coordinates and the output is typical as given in TABLE-1.



The polar coordinate marking is done using the apparatus that is put up for patent.
The sketch of the apparatus is an attached at end of this specification paper as Fig.-3.
The marking is carried out after running the software and changing the Cartesian
coordinates to polar coordinates as explained in the previous section. The swinging
arm and the marking punch, which can be dismantled are mounted on the centre
pivot pin attached to the graduated base. The graduated base is seated on the
manhole door opening. The graduated base has alien keys that are used to centre its
position with respect to the man hole door opening; having centred the apparatus on
the man hole door, the angles are incrementally located on the graduated base, as
seen from the software output. Once the

angle is pointed, the radius shall be marked using the sliding assembly, which has the
marking punch held in its slot. The marking punch is moved vertically and the punch
mark is obtained on the dished end profile.
(Numbers in bracket correlate to the numbers in Fig.-3)
The fixture (Fig.-3) has a graduated base round plate (1), on which a centre pivot pin
(2) is fixed. The second assembly (22) is for the radius transfer on to the curved
surface. The assembly has a calibrated scale on a swing arm (4), along with which it
is fastened to a thick cylinder with a bore, called the Arm mounting cylinder (3). There
is a distance locator sliding block, comprising of two parts, Sliding Block 1(5) and
Sliding block 2(6) as shown in the Fig. -3. The sliding block is held intact by using a
spacer piece (10). The marking punch (7) is attached to these sliding assembly. The
punch can be lifted to any height that is suitable to transfer the radius point on the
surface of the dished end. The swing arm also has an angle pointer (8), which
indicated the angle used in the marking process. There is a handle (9) provided for
rotating the arm to point the angle. There are different size screws for fastening
purpose. These come in the assembly (11, 12, 13, 14, 15 & 16, 17, 18). The top of
the central pivot arm can be tightened by a washer (20) and a bolt (19).

WE CLAIM
1. An apparatus for marking drill hole locations on curved surfaces comprising;
a graduated base round plate (1);
a centre pivot pin (2) fixed on it;
a cylinder with a bore called the arm mounting cylinder (3) mounted on the
centre pivot pin (2);
the swing arm (4) fixed to the arm mounting cylinder (3) by fastners;
Characterized in that,
the radius transfer assembly (22) is mounted on the swing arm (4) wherein the
marking punch (7) is loaded in the slot such that the swing arm (4) can rolate
at any angle wherein the sliding blocks moves radially to position the marking
punch to the polar co-ordinate point to be marked at dished end of curved
surfaces;
2. An apparatus as claimed in claim 1 wherein the sliding block assembly or the
distance locator (21) comprises two parts, sliding block (5) and sliding block (6)
held intact by a spacer piece (10).
3. An apparatus as claimed in 1 wherein the graduated base round plate (1) is
marked 0-360°.
4. An apparatus as claimed in claim 1 wherein the swing arm (4) is attached with
a marking scale.

5. An apparatus as claimed in claim 1 where in handle (9) is fixed with the arm
mounting cylinder (3) for rotating the base round plate (1) to a desired angle.
6. An apparatus as claimed in claim 1 wherein the swing arm (4) has an angle
pointer (8) for indicating the angle used in the marking process.
7. A method of marking drill hole locations on curved surfaces by the apparatus
claimed in claim 1, comprising;
converting the cartesian co-ordinates to polar co-ordinates by a processing
mean;
mounting the swing arm (4) and marking punch (7) on the centre pivot pin (2)
attached to the graduated base round plate (1);
Placing the graduated base round plate (1) on the man hole door opening;
Characterized in that
Centering the graduated base round plate (1) with respect to the man hole
door opening by the alien keys present in the base;
Locating the angles incrementally on the graduated base (1) with the help of
angle pointer (8);
marking the radius using the sliding assembly (21) at desired angle wherein the
marking punch (7) is held in the slot of sliding assembly (21) that moves
vertically to give punch mark at desired location. ^-^

Boilers, pressure vessels or heat exchangers have pressure bound components that are
fabricated may be designed as hemi spherical, semi ellipsoidal or torispherical. The present
manufacturing drawing gives the drill holes that form the openings on the dished ends of
boiler / pressure vessel or a heat exchanger as Cartesian coordinate points. The points are
given in a Cartesian coordinate system as shown in Fig.-1.
With the present scenario depicted in the prior art, a need to simplify the marking
methodology was imperative and hence the apparatus was conceived. The apparatus is
supported by an in-house developed software that converts the input Cartesian coordinates to
output polar coordinates (Fig.-2). The polar coordinate marking is done by using the
apparatus that is put up for patent. The sketch of the apparatus is as attached at Fig.-3. The
marking methodology and the apparatus are as follows.
The fixture has a graduated base round plate (1), on which a centre pivot pin (2) is fixed. The
second assembly is the radius transfer assembly called the sliding arm. The assembly is
having a calibrated scale on a swing arm (4), along with which it is fastened to a thick
cylinder with a bore, called the arm mounting cylinder (3). There is a distance locator sliding
block, comprising of two parts, sliding block 1 (5) and sliding block 2 (6) as shown in the Fig.-
3. The sliding assembly is held intact by using a spacer piece (10). The marking punch (7) is
attached to this sliding block assembly. The punch can be lifted to any height that is suitable
to transfer the radius point on the surfacr of the dished end. The swing arm also has an angle
pointer (8), which indicates the angle used in the marking process. There is a handle (9)
provided for rotating the arm to point the angle. There are different size screws for fastening
purpose that come in the assembly (11,12,13,14,15,16,17 and 18). The top of the central
pivot arm can be tightened by a washer (20) and a bolt (19).