Field of Invention
The present invention relates to a fixture for turning of various large commutator. More particularly the invention relates to a fixture of universal application which comprises base plate mounted over L-shaped angular plates and tool post with the tool stone is mounted over the said base plate. The height of tool post is adjustable so as to bring the tool tip at neutral position of the armature during turning.
Back ground of the Invention
In the conventional turning device for commutator turning, the top part of rocker ring is removed and bottom half ring is brought to almost vertical position for giving supply at magnetic neutral point of brushes. This is necessary to mount the tool post girder and the tool. The tool post is mounted over a suitable pair of girders (I-beam) specially made for each machine. The size of the tool post girders is determined by height of neutral point available above the base plate of motor. Hence different sized armature needed different sized tool post fixing girder arrangement.
This method is unsafe and involve lot of man power and time during shifting of rocker ring and back to position. Also, each machine required its own tool post girder. The rocker ring shifting and repositioning requires very high skills and concentration of the operator and rigger.
Moreover the neutral point is to be correctly defined to avoid frequent damage of turning tools and provide satisfactory smoothness in the turned surface. Besides this the tips of tools will glow while turning and it gets blunt.
The inventors have now found a fixture which could fit on various commutators and without the laborious task of removing the rocker ring. The fixture is fitted parallel to the shaft of the armature and has adjustable tool post on which the tool is mounted which touches previously determined the neutral point.

Objects of the Invention
Thus the basic object of the present invention is to provide a fixture for commutator turning of commutators of various sizes
It is a further object to provide a fixture which eliminates difficulty in finding the neutral point and thus is safe and economical.
Statement of the Invention
Thus according to main aspect of present invention there is provided an adjustable fixture for turning of a commutator comprising:
i) a tool post;
ii) a pair of L-shaped angular plates;
iii) a base plate;
iv) a means for turning
wherein the said base plate is mounted over the said L-shaped angular plates and the said tool post with the said means is mounted over the said base plate such that the tool post is adapted to be inserted between rocker ring and commutator of the machine and the fixture is adapted to be set parallel to the shaft of the armature of the commutator, wherein said tool post is adapted to be of adjustable height
Detailed description of the invention
The fixture of the present invention is mounted with turning tool adapted to turn the commutator at neutral point. The turning tool is set at neutral Axis of commutator of machine since neutral point commutator has low voltage and safe to operate/handle. This fixture of the present invention may be used for of commutator surface.
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The commutator turning fixture of the present invention can be used in all the machines where the gap of rocker ring and commutator is more than 150mm This is applicable for large size of machine preferably above 400 kw armature
The angular plates of the fixture has slots which help in adjustment of various height. So the neutral point of tool, is very easily set on the commutator by adjusting the angular plates for various sizes and types of D.C. Machine.
For smaller armature one pair of smaller angular plates is also made to facilitate easy handling and fixing.
The tool touches the commutator at 90° or less in the suitable direction of rotation. The fixture is set parallel to the shaft of armature so that the tool tip touches / turns the same segment. The tool is mounted in such a way that all the commutator length turning is possible. In some cases special tools are made which are slightly bent in the direction left or right for turning near the riser and grove cutting. All the turning tools should be properly insulated so that it could be easily inserted in the tool holder of the tool post for tightening and then turning the commutator. Accordingly insulated carbide tipped tools are preferred.


The machine is rotated at low speed by low armature voltage. Since turning is done with tool at magnetic neutral Turning speed is 120 meter / minute at-toe-curfimutaTSr fcuoace.

The fixture may be used for turning commutator of the machine which is coupled with other variable speed drive. In that case turning is done at central height of armature or little below the central Axis of shaft for better result It is not necessary to check the neutral points etc because the rotation is being done by other coupled machine for rotation purpose.
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Similarly other machine also can be turned giving supply to this machine after under cutting and beveling if drop tests is found satisfactory. In all these cases tandem connected sets are preferred. All these are required for large capacity of armatures of commutators.
Turning on pedestal turning on pedestal have given better commutator surface finish and virtually no beating. Turning with device give much better result as compare to turning on lathe machine.
In some of the machines where the length of armature is more and the cantilever of mounted tool post is high a side support could be welding with angle/channel. It will also help in arrest the vibration while turning.


Brief description of accompanying figures
Fig 1 shows a schematic diagram of the alignment of fixture-Fig 2. shows a view of the fixture in working position Detailed description of accompanying drawings
Fig 1: L shaped angular plates (1) for base plate(2) mounting. The base plate provided with bolts (3) for fixing tool post in the grooves (4). The angular plates are attached with position of the rocker arm (5) indicated by dotted lines with the help of washer (6), nut (7) and studs (8).
Fig 2: For turning at neutral point the top rocker arm is maintained at original position while the bottom one is removed
Both "L" shaped angular plates(1.) are fixed on both side of rocker ring (9) in such a way that the gap is left for rotation of armature angular plate nut (7). The gap between both
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angular plate is maintained with discs / washers of thicker sizes specially prepared for increasing the gap between to "L" shaped plates. This gap depends on the length of commutator. Better results are achieved if the gap between angular plates is between 100 to 300 mm. Both the angular plates projections are towards the commutator side for mounting the base plate (2).
Base plate(2) is fixed on angular plates(1) uniform level so that tool post is fixed on the base plate. After mounting the tool post on the base plate and tool in the tool holder(10), the cutting tip (11) of the tool touches at the neutral point (12) of armature.
The slight variations in the height of the neutral line with respect to tool tip is adjusted by movement of angular plates up and down so that tool tip touches the armature neutral point . The base plate is fixed on angular plate from the top and tool post is tightened from the bottom of base plate. In all the situations the neutral height is maintained.
Alignments of tool post is checked so that the commutator is turned parralled to the shaft axis, by checking the gap between commutator and the tool tip with a filler gauge, at both the ends of the commutator along the length of segment of commutator/bar. In absence of such checking for parallelism, the taper turning may lead to an uneven cutting of the commutator.
Tool post insertion is made from the side at pedestal end. It is placed in such a way that the fixing of base plate and tightening of tool post is easily possible. .
Commutator movement is rotated in correct direction of rotation, such that the tool surface comes from up to down side for cutting the commutator surface. All these types of turning is preferred for the large capacity of armatures.
Working of the Invention
For positioning the fixture of the present invention the motor is stopped and covers at commutator end is removed.
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4'0 clock / 8'0 clock brush arm having brush holder mounting upward is removed. The center of the brushes is marked at edge of commutator.
The gap between tool holder edge( figure 2) and commutator surface should not be more than 50 mm, otherwise it may lead to vibration and rough-surface of turned In large DC machines, the 6 o'clock arm is situated at the bottom of the machine, and the 4 o'clock and the 8 o'clock brushes are at the two positions just below the central axis of the equipment. When the tuning tools are fixed in the 12 o'clock to 3 o'clock and 9 o'clock to12 o'clock positions, they are inoperative as the copper chips tend to stick to the turning tools while turning operation is carried out, which may spoil the commutator surface by sparking between segments. On the other hand, 5-7 o' clock positions are placed at the lower part of the machine, which may be below the pedestal in most of the machines. Therefore, only 4 o' clock & 8 o' clock are the only positions where the turning toots can be fixed. These positions have advantages as turning chipps directly moves away from the commutator and goes down. The turning person can easily operate the turning tools and it suits to his posture for working. As this is done with supply, all the emergency switches are in approach in case of any emergency to switch off turning system.
Rocker arm is removed for mounting of the turning fixture.
Pair of L-shaped angular plates are fixed on both side of rocker ring after providing suitable spacers between the two angular plate, so that base plate could be mounted for tool post.
Base plate mounting and its arrangement with angular plates, rocker ring and tightening with the angular plates are such that fixing are in a plain for mounting of tool post. (Figure 1) Different holes are also provided for adjustment of tool
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post mounting, so that tool post can be properly fixed to turn the commutator full length particularly at the end.
The tool post is mounted on the base by fixing the 4-bolts in the bottom groves provided in the tool post. The distance between bolts are adjusted as per the holes selected for tightening of tool post. The minor adjustment and required gap between armature risers and tool post is provided in such a way that tool post end bolts do not touch the riser and commutator is turned ,upto end also.
As far as tool post suitability for fixing of the tool is to be checked with armature shaft as the reference. After tool post mounting it is observed that the tool post front part is slightly elevated. The tool posts are designed in such a way that by interchanging some of the parts, it is used for reverse rotation for turning of commutator.
The tool post alignment for commutator turning is done by mounting a dead tool or a pointed rod in the tool holder by measuring the gap on the commutator surface between tool and commutator. Alignment of tool post must be equal at both end of commutator. It should be checked with the help of filler gauge.

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commutator. These gaps can be adjusted by changing the angle of mounting or packing in the angular plate adjustment in the studs in upward or downward. All the attachment tightness is to be checked. If there is more cantilever towards pedestal side a side support may be welded to the base plate.
The rotation of armature should be in anticlockwise direction for the particular arrangement. If the rocker arm is removed at 4'0 clock the rotation could be of clockwise direction.
Turning tool to be fixed in the tool holder and tool should be made of carbide types and arm should be insulated which can withstand voltage up to 500 v.
As per direction of rotation speed for turning can be adjusted. The speed of rotation should not be more than 120 m/min.
Tool cutting depth can be made by the adjustment for feed provided in the stide in the cross side.
The stide is moved with tool by rotating the tool post handle provided in the side of tool post near the pedestal side.
Rotation of screw move the tool holder for turning through the box-nut provided in the cross stide of tool post.
Now the rotation may be done at low rpm at low voltage and low current in the armature circuit.
Touching to armature near the brushes neutral is safe and but not at other points
All the time turning should be made on commutator from starting to end and any space left in between may lead to extra cutting and copper deposited between the segments leads to shortening of armature and heating of commutators. So whenever there are
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shortening in between segment it should be undercut and removed before starting turning again.
After getting the finished surface, sand papers to be applied for removal of turned and better finish.
Advantages
The fixture of the invention has following advantages :-
(1) The fixture has universal application for large machines.
(2) The risk to life and property while removing and shifting back of rocker ring of
machine is totally eliminated. The time taken in the job is reduced to 6-8 hours
from 40-48 hours.
(4) Eliminated mistakes in finding out neutral point and workmen are not required for checking the neutral point of commutator.
(6) Eliminates requirement of cranes and other work force.
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We claim :
1. An adjustable fixture for turning of a commutator comprising: i) a tool post;
ii) a pair of L-shaped angular plates (1); iii) a base plate(2); and iv) a means for turning
characterized in that the said base plate (2) is mounted over the said L-shaped angular plates (1) and the said tool post with the said means is mounted over the said base plate such that the tool post is adapted to be inserted between rocker ring and commutator of the machine and the fixture is adapted to be set parallel to the shaft of the armature of the commutator, such that said tool post is adapted to be of adjustable height.
2. A fixture as claimed in claim 1 wherein the said means for turning is tool.
3. A fixture as claimed in claim 2 wherein the tool is insulated carbide tipped and
placed in the tool holder in the tool post.

4. A fixture as claimed in any preceding claim adapted to be fitted on the armature such
that the tip of the tool stone touches the neutral point of the armature.
5. A fixture as claimed in any preceding claim adapted to be fitted on the armature such
that the tip of the tool stone touches the armature at 90° or less
6. A fixture as claimed in any preceding claim adapted to be fitted on the armature of the commutator by the said L shaped angular plate being mounted on hole of brush arm replacing a brush arm.
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7. A fixture as claimed in claim 6 wherein the said L shaped angular plates are adapted to be
fixed on both sides of the rocker ring such that a defined gap is left for rotation of
armature
8. A fixture as claimed in any preceding claim wherein the tpol post height is adapted to be
adjusted such that the tool touches magnetic neutral point of the armature of the machine.
9. A fixture as claimed in any preceding claim wherein the angular plates are provided with
slots at various height for adjustment of tool post height for adapting to machines of
various sizes.
10. A fixture as claimed in any preceding claim further comprising an angle/channel adapted
for turning machines with long armature.
11. A fixture as substantially herein described and illustrated in the figures.
A fixture for turning of various large commutator. The fixture is of universal application and comprises base plate (2) mounted over L-shaped angular plates (1) and tool post with means for turning is mounted over the said base plate. The fixture is such that the tool post is adapted to be inserted between rocker ring and commutator of the machine and the fixture is adapted to be set parallel to the shaft of the armature of the commutator. The height of the tool post of the fixture is adjustable so as to bring the tool tip at neutral position (12) of the armature during turning.