The present invention relates to a jig/device (D) for marking Pitch Circle
Diameter (PCD) on any disc type object with known outer diameter.
BACKGROUND OF THE INVENTION
Pitch circle diameter is the diameter of an imaginary circle passing through the
center of bolts distributed around a component such as a wheel, hub or housing. Once
the pitch circle diameter is established, one need only specify the number of holes or
threads and dimensions of each hole or thread to describe the full bolt pattern.
For two meshing gears, the pitch circle diameter represents each of two
imaginary friction discs that, when spun together without slippage, would result in the
identical velocity ratio and gear ratio as the actual gears. The pitch circle diameter is
thus an important geometrical term for engineers in describing the mechanical
relationship of a gear set.
In more layman terms, a pitch circle diameter will always remain less than the
actual diameter of the object and it's kind of inward radial offset to some distance from
the outer diameter, (refer fig. 1)
In general, a divider is used to mark the PCD of holes in plates of different
diameters.

Using divider in case of small diameter is not an issue but in case of large
diameters it is not as easy task to use the divider. Dividers are used to mark up circles
and arcs. They are held at an exact angle by an adjusting nut. Because of the sharp
points on their legs, they also give an accurate way to transfer measurements from say,
a steel rule, across to the work. Pin point the lines on the rule and make sure the circle
has exactly the right radius. One way to make sure this leg of the dividers stays put on
the surface is to make a small dent with the prick punch, before starting to draw.
For equipment like power plant components, there is a frequent need of marking
diameter for the center of a disc type object and accuracy in marking this diameter is
necessary. This markings are used to drill holes or take reference of any other marking
etc.
The issue in using divider was that:
1. most of the components are metals and it was not easy to keep hold of the leg
of the divider at its position (refer fig. 2). Therefore there was high chances of
inaccuracy.
2. The height of the instrument (divider) decides the span of the divider of the
maximum diameter which the divider can measure. So in components in which the
diameter is to be marked in thousands of mm, the height of the instrument will reach in
feet which is difficult to work with. Alternatively, a big diameter can be divided into

number of small diameters. The divider can be progressively used to measure small
diameters to measure the bigger diameter but it is too time consuming and will increase
errors due to fatigue to the workmen.
For the same, it was required to develop a marking jig that can mark pitch circle
dia or in general any diameter on the disc. A marking jig in place of divider was
designed to mark the PCD in which the difference between the maximum diameter and
the PCD can be filled on the scale mounted on the jig and the with the help of two
bearings it can be moved all around the plate or any round object without any difficulty.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a jig/device for marking
pitch circle diameter on any disc type object with known outer diameter, which is
capable of marking PCD for any diameter of the workpiece, large or small.
Another object of the invention is to propose a jig/device for marking pitch circle
diameter on any disc type object with known outer diameter, which is able to make PCD
on the workpiece case, accuracy and very fast resulting reduction in cycle time.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1: Shows the pitch circle diameter (PCD) of two mating gears.
Fig. 2: Shows a diameter marking instrument called divider.

Fig. 3: Shows the marking jig according to the invention.
Fig. 4: Shows the slotted segment of the jig according to the invention.
Fig. 5: Shows the rolling device of the jig according to the invention.
Fig. 6: Shows the semicircular segment of the jig according to the invention.
Fig. 7: Shows the jig on a work piece W for the marking the PCD.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
According to the present invention, the invented jig for marking pitch circle
diameter comprises of the following items:
Item 1. Slotted segment.
Item 2. Slot of slotted device (1).
Item 3. Semicircular segment.
Item 4. Plurality of rolling device.
Item 5. Bearing to support rolling device (4).
Item 6. Marker.
Item 7. Circular slot for putting marker (6) in slotted segment (1).
Item 8. Threaded hole on Item-3 for rolling device (4).
Item 9. Threaded hole for setting screw (11).
Item 10. Threaded hole for screw to fix marker (6).
Item 11. Setting screw.

The marking jig is shown in Fig.3. The slotted segment (1) as shown in Fig.4
has a slot (2) to facilitate the adjustment of length of measurement (diameter from the
outer periphery of the disc). The semicircular segment (3) as shown in fig.3 has a
longitudinal movement through the slot (2). The length and width of the slot is
predetermined.
The semicircular segment (3) is connected to slotted segment through a
threaded connection between that passes through the slot (2) of the slotted segment
(1) and then to the threaded hole (9) provided on the point of maxima on the
semicircular curve of semicircular segment (3).
The setting screw (11) is selected in such a way that its hex size (size of the
head of the screw) is greater than the width of the slot (2) and the nominal diameter of
the screw is less than the width of the slot thereby ensuring that setting screw (11) can
have longitudinal movement in the slot (2) required to adjust as per the required
dimension to be marked, (refer fig. 6 for screw nomenclature)
Semicircular segment (3) also consists of plurality of threaded holes (8) that will have
threaded connection with plurality of rolling device (4). The rolling device are disc type
in shape.
The rolling devices (4) are enclosed in roller bearings (5).

It is to note here that unlike general situations in which the roller bearings are
steady and support the roller such that the roller will rotate, here the rolling device (4)
(refer fig. 5) is fixed through threaded connection with threaded holes (8) and the
bearings will roll over the disc's (job on which marking is to be done) outer periphery.
Rolling devices (4) are installed specifically on semicircular segment (3) so that
segment does not foul with the curved part of the job. (since the job is a disc, its curve
will also be circular)
The marker (6) which is of cylindrical shape having a tip at its one end capable
of creating indent on the surface of the job to do the marking.
A circular slot (7) is provided on slotted segment (1) for putting the marker in it
and then fixing the marker at required position through a screw using threaded hole
(10) at the extreme end of the slotted segment (1). Marker (6) will be installed
perpendicularly to the slotted segment (1), marker (6) is installed perpendicularly to the
slotted segment (1).
Method for using the developed marking jig
1. The distance from the outer periphery of the job (W) is marked. Let the radius of
the job is X unit and pitch circle diameter is at Y unit, then the marking is to be done
manually using a ruler at a distance (X-Y) unit from the periphery of the job (W).

2. The bearing (5) is placed on the periphery of the disc/work piece (W) as shown
in Fig.7.
3. The length is adjusted using the adjustable screw (11) so that the tip of the
marker (6) is on the point marked manually using the marker (6).
4. The device/jig (D) is set on the required length from the periphery.
5. The device (D) is rotated on the periphery of the job the marking wherever
required, when if necessary the height of the marker is adjusted by the help of the
screw (10).

WE CLAIM
1. A jig/device (D) for marking pitch circle diameter (PCD) on any disc type object
with known outer diameter comprising;
a slotted segment (1) having a slot (2) with predetermined length and width;
a circular slot (7) disposed in the slotted segment for providing a marker;
a marker (6) of cylindrical shape having a tip in its one end disposed in the
circular slot (7);
a threaded hole (10) at the extreme end of the slotted segment (1) for
tightening the marker (6);
characterized in that,
a semicircular segment (3) having threaded holes (8) for fixing a plurality of
rolling devices (4) enclosed in roller bearings (5), is fixed to the slotted segment (1) by
a hexagonal setting screw (11) in a threaded hole (9) provided on the point of maxima
on the semicircular curve of semicircular segment (3);
when the bearings are disposed for rolling over the disc/job when placed on the
periphery of the job wherein the rolling devices are disposed for preventing the said
segment (3) from fouling with the curved part of the job; wherein the marker (6) is
disposed in the slotted segment (2) for marking a Pitch Circle diameter on a disc type
job after the device /jig (D) is set on the required length from the periphery.

2. The jig as claimed in claim 1, wherein the marker (6) being of cylindrical shape is
disposed in the circular slot (7) perpendicularly to the slotted segment (1) and adjusted
at any position by a screw at threaded hole (10) on the slotted segment (1).
3. The jig as claimed in claim 1, wherein the rolling devices (4) are disc type in
shape.
4. The jig as claimed in claim 1, wherein the hexagonal size of the head of setting
screw (11) is greater than the width of the slot (2).
5. A method for marking Pitch Circle Diameter on any disc type object with known
outer diameter by a jig claimed in claim 1, comprising;
marking the distance from the outer periphery of the job manually, the said
distance being equal to radius of the job (W) minus PCD;
placing the bearings (5) on the periphery of the job (W);
adjusting the length by the adjustable screw (11) to set the tip of the marker (6)
on the point marked manually; wherein the jig (D) is rotated on the periphery of the job
(W) to set the tip of the marker (6) at the required point when the jig (D) is set on the
required length for marking the Pitch circle diameter.