FIELD OF THE INVENTION
This invention generally relates to retrofitting a single axis Length Measuring Machine of least count 0.001 mm (1 µm) used in Metrology for calibration of various instruments like inside micrometer, rods of outside micrometer. More particularly, the invention relates to a method of retrofitting a single axis length measuring machine for calibration of micrometers to provide accurate measurement of objects.
BACKGROUND OF THE INVENTION
Length measuring Machines are generally made of ‘Cast Iron’, having at least an optical system. With the passage of time, the optical system develop defects for example visibility of scales of the system becomes very poor or there are no scales at all visible.
As the prior art machines are made of cast iron, the body of the machines become more and more stable with time in other words, there is no defect in the base of the machine. For retrofitting of the machine, only thing to be taken care of is that the measurement of the movement of the two heads of the machine in microns. We have deployed a dial indicator of Least count 0.001 mm for such measurement and for the movement of one of the head we have designed a pulley system.

OBJECT OF THE INVENTION
It is therefore an object of the invention to propose a method of retrofitting a single axis length measuring machine for calibration of micrometers to provide accurate measurement of objects.
SUMMARY OF THE INVENTION
Accordingly, there is provided a method of retrofitting a single axis length measuring machine for calibration of micrometers to provide accurate measurement of objects, the length measuring machine comprising a base two heads, a micrometer head, a first stand to fix the micrometer for calibration, a plurality of poles to hold the machine, the method comprising the steps of providing a second stand configured with two sets of threaded holes, the first set of holes is used to fix the second stand on the machine, providing a dial indicator of least count one micron which is fitted on the second stand via the second set of holes locating a pulley formed of a ring with a bearing press-fitted, a groove configured on the outer surface of the ring to allow a string to be moved along the pulley, positioning a third stand such that a part of the stand can hold the pulley via an axle, the pulley having end weights to pull the second machine head connecting the axle with a shaft of the pulley via a third set of threaded holes, the part of the thirds stand being fixed to the stand through a fourth set of threaded holes; wherein the sub-assembly of the third stand is fixed to the single axis length measuring machine through a fifth set of threaded holes using a plurality of screws.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows top view of an existing Length measuring machine which comprises:
1) Micrometer head which is calibrated by length measuring machine,
2) Two heads of the machine (Head A and Head B),
3) Base of the Machine,
4) Stand to fix the micrometer which to be calibrated.
Figure 2 - shows a front view of the length measuring machine of Figure 1, indicating
5) Cemented polls to hold the complete machine.
Figure 3 - shows a top view of Length measuring Machine modified according to the invention, the modification essentially includes the features :
6) a Pulley.

7) a Nylon String attached to head B and weights,
8) a Dial Indicator least count 0.001 mm,
9) a Stand to hold the Dial Indicator,
Figure 4 – shows front view of the modified length measuring machine of Figure 3 emphasizing the further features of :
10) a Stand (attached to Length Measuring Machine) to hold the pulley,
11) Weights to pull the Head B.
Figure 5 – Shows the front view of the modified length measuring machine emphasizing the features :
12) threaded Holes to tighten the stand (9) on original base of length measuring machine,
13) a threaded Hole to tighten the dial indicator (8) on the stand (9). Figure 6 - Shows dimensions of a ring used to form the pulley (6),
14) Space to fix the bearing in the ring to convert it into pulley (6).

Figure 7 - Shows dimensions of the stand (10) to hold the pulley (6) using a
shaft:-
15) Threaded holes to hold the shaft of pulley (6).
16) Threaded holes to fix the stand (10 on base (3).
Figure 8 – Shows the shaft which is used to fix the pulley on the stand shown in Figure 7.
Figure 9 – Shows stand to be fixed on the existing length measuring machine :-
17) Threaded hole where the stand is fixed as shown in Figure 7,
18) Threaded holes to fix the stand on the length measuring machine. Figure 10 - Complete assembly of the features shown in Figures 6, 7, 8, 9
19) Bearing provided to the pulley (6),
20) Ring shown in Figure 6,
21) Stand shown in Figure 7.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Figure 5 shows the strand (9) on which the dial indicator (8) is fixed. With the threaded holes (12), this stand (9) is fixed on the Length measuring machine as shown in Figure 3. In the threaded hole (13) of this stand (9), the dial indicator (8) of least count 1 micron is fixed. For keeping the dial parallel to the base, flatness of the faces of the stand (9) is maintained very accurately.
Figure 6 shows a ring which is used in forming the pulley (6). For constructing the pulley, a bearing (19) is press fitted inside the ring as shown in Figure 6. A groove is cut on the outer surface of the ring so that a string (7) can move easily on the ring.
Figure 7 shows a part of the stand (10). This part is used to hold the pulley (6) with the help of an axle shown in Figure 8. With the help of the threaded holes (15), the shaft is fixed on it and with the help of the threaded hole (16) this part is fixed on the stand shown in Figure 9.
Figure 8 shows the dimensions of the shaft which holds the pulley (6). This shaft is mounted on the part of the stand (10) as shown in Figure 7.

Figure 9 shows the stand (10) which is attached on the length measuring machine with the help of a plurality of screws (18). With the help of the threaded hole (17), the part shown in Figure 7 is attached on the stand.
Figures 1 and 2 shows front and top view of Length measuring machines.
Figures 3 and 4 shows the modified length measuring machine. Figure 10 shows the complete assembly of the components used in modification of the machine, and shown in Figures 6, 7, 8 and 9.
MODE OF OPERATION OF THE MODIFIED LENGTH MEASURING MACHINE OF THE INVENTION
Method of length measurement in modified length measuring machine is basically a calibration (comparison). Calibrated length bars are used in calibration. Suppose length of 520 mm is to be measured. For this, the dial indicator has to be first set at zero, using a calibrated length bar of 500 mm. Length bar is set on the stand (4).
After setting zero in the dial indicator, only head B is moved right side and is returned back by pressure of the string attached to the pulley. Due to the pulley system pressure exerted by the head B is same in setting zero as well as at the time of taking readings. This makes readings more accurate.

The range of the dial indicator is 25 mm. So after setting the zero once, a distance up to 25 mm can be checked. Dial indicator shows readings with positive and negative sign. So if reading is + 5 µm and the dial is set zero at 100 mm then the actual length of the object is 100.005 mm.
This method can be deployed for calibration of inside micrometers and outside micrometers up to range 1000 mm. As the length bar of more than 1000 mm is not available, so this method of retrofitting could be used only upto the range of 1000 mm.

WE CLAIM :
1. A method of retrofitting a single axis length measuring machine for
calibration of micrometers to provide accurate measurement of objects, the length measuring machine comprising a base (3), two heads (2A, 2B), a micrometer head (1), a first stand (4) to fix the micrometer for calibration, a plurality of poles (5) to hold the machine, the method comprising the steps of :
- providing a second stand (9) configured with two sets of threaded holes
(12, 13), the first set of holes (12) is used to fix the second stand (9) on
the machine;
- providing a dial indicator (8) of least count (1) micron which is fitted on
the second stand (9) via the second set of holes (13);
- locating a pulley (6) formed of a ring with a bearing press-fitted, a groove configured on the outer surface of the ring to allow a string to be moved along the pulley (6),
- positioning a third stand (10) such that a part of the stand can hold the pulley (6) via an axle, the pulley (6) having end weights to pull the second machine head (2B);

- connecting the axle with a shaft of the pulley (6) via a third set of threaded holes (15), the part of the third stand (10) being fixed to the stand (10) through a fourth set of threaded holes; wherein the sub-assembly of the third stand (10) is fixed to the single axis length measuring machine through a fifth set of threaded holes (17) using a plurality of screws (18).