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- The indexing is the operation of dividing the periphery of a workpiece into any number of equal parts.
- While cutting the spur gear, an equal spacing of the teeth on the gear blank is performed by indexing.
- The indexing can also be used for producing a square or hexagonal bolts, cutting splines on shafts, fluting drills, taps, reamers, etc.
- The indexing can be achieved by using a special attachment known as dividing head or index head.
There is a total of 5 Indexing Methods:
- Direct Indexing
- Simple Indexing
- Angular indexing
- Compound Indexing and
- Differential indexing
1. Direct Indexing:
The direct indexing is also called Rapid indexing, and it is used when a large number of pieces are indexed with a small division.
This operation can be done in both plain and universal dividing head. When using the Universal head, the worm and worm wheel are first disengaged.
The required number of division on the work is obtained by means of the rapid index plate which is fitted at the front end of the spindle nose. The plate has 24 equally spaced holes.
The spring loaded pin can be pushed into any of the holes to lock the spindle with the frame.
For indexing, the pin is taken out first and then spindle is rotated by hand, and after the required position is reached it is again locked by the pin.
When the plate is turned through the required part of the revolution, the dividing head spindle and the work are also turned through the same part of the revolution.
With Rapid indexing plate of 20 holes, it is possible to divide the work into an equal division of 2,3,4,6,8,12 and 24 parts which are all the factors of 24.
To Find the index movement, find the total number of holes in the direct index plate by the number of divisions required on the work, If N is the number of divisions required on the work then,
[Number of holes be removed= 24/N]
2. Simple Indexing:
Simple indexing is also called as 9 indexing. It is more accurate and has a large range of indexing than rapid indexing.
FOr indexing, the dividing head spindle is turned by the by index crank. The figure is shown:
The worm shaft carrying the crank has a single threaded worm which meshes with worm gear having 40 teeth, 40 turns of the crank are necessary to rotate the index head spindle through one revolution.
Therefore, one complete turn of the index crank will cause the worm wheel to make 1/40 of a revolution. To facilitate indexing to the fraction of a turn, Index plate is used to cover practically all number.
The Index plate with a circle of holes manufactured by the brown and sharp company are:
- Plate No 1- 15,16,17,18,19,20
- Plate No 2- 21,23,27,29,31,33
- Plate No 3- 37,39,41,43,47,49
To find the index crank movement, divided 40 by number of division required on the work,
[Index crank movement= 40/N]
Where N is the number of division required on the work.
3. Angular Indexing:
The angular indexing is the Process of dividing the periphery of work in angular measurements. There are 360 degrees in a circle, and then the index crank is rotated by 40 number of revolution, and the spindle rotates through 1 complete Revolution or by 360 degrees, one complete turn off the crank will cause the spindle and the work to rotate through 360/40=9 degrees.
Therefore in order to turn work through a required angle, the number of turns required for index crank can be calculated by the number ‘9’. If an angular displacement is expressed in minutes then the terms of the index crank can be calculated by dividing the angle by 540.
If it is expressed in seconds then it is divided by 32400.
If the result is a whole number, the index crank is rotated through the full calculated number.
If the result is whole number and fraction, the part of the revolution of the crank after turning the whole number is calculated by multiplying is suitable for numbers to the numerator and denominator of the fraction, defecation to make the denominator of the fraction is equal to the number of holes in the index plate circle and the now numerator number for holes to be moved by the index Crank.
The index crank Movement= Angular displacement of work, in degrees / 9
= Angular displacement of work, in minutes / 540
=Angular displacement of work, in seconds / 32400
4. Compound Indexing:
In Compound indexing, there are two separate movements of the index crank in two different hole circles of one index plate to get the crank movement.
The index plate is held stationary by Lock pin heed which engages with one of the whole circle of the index place from the back.
For indexing first, the crank pin is rotated by the required number of the spaces in one of the holes of the circle of the index plate and then the pin is engaged with the plate.
The second index movement is done by removing the real lock pin and the rotating the plate together with the index crank forward or backward through the calculated number of spaces of another hole circle, and the lock pin is engaged.
The net movements are the sum of the movement, therefore,
[40/N = n1 /N1 + n2/N2]
Where N is the number of divisions required
N1 is the hole circle used by the crank pin
N2 is hole circle used by the lock pin
n1 is space moved by the crank pin in N1 hole circle
n2 is the spaces moved by the plate and the crank pin in N2 hole circle.
The basic knowledge about indexing, I think now you know. So let’s look forward to solving the problem,
Q 1. Find out the index movement required to mill a hexagonal Bolt by direct indexing. The rapid index plate has 24 holes.
Solution: Number of holes to be moved = 24/N
Therefore after machining one side of the bolt, the index plate has to move by 4 holes for next face to the machine.
Q 2. Set the dividing head to mill 30 teeth on spur wheel blank by simple indexing.
Solution: Index Crank movement = 40/N
= 4/3 * 7/7 =1+(7/21)
1 Full turn and 7 holes in 21 holes circle of the index plate.
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