Indexing Head-Definition, Methods, Formula, Indexing in Milling Machine [PDF]

What is Indexing Head?

The indexing head is the operation of dividing the periphery of a workpiece into a number of equal parts. While cutting the spur gear, an equal spacing of the teeth on the gear blank is formed by indexing. The indexing head can also be used for producing 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.

Methods of Indexing Head

  1. Direct Indexing
  2. Simple Indexing
  3. Angular indexing
  4. Compound Indexing
  5. Differential indexing

Let us discuss each method in detail.

Direct Indexing Head

The direct indexing is also called Rapid indexing. 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 divisions 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. 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 a 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 in the work. If N is the number of divisions required on the work then, Number of holes to be removed= 24/N.

Simple Indexing Head

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 index crank. 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, an Index plate is used to cover practically all numbers.

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, divide 40 by  number of division required on the work, [Index crank movement= 40/N], Where N is the number of divisions required on the work.

Credits : AniMech

Angular Indexing Head

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. The spindle rotates through 1 complete Revolution or by 360 degrees. One complete turn of the crank will cause the spindle and the work to rotate through 360/40=9 degrees. Therefore, in order to turn the work through a required angle, the number of turns required for index crank can be calculated by the number ‘9’.

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. When a result is a whole number, the index crank is rotated through the full calculated number.

If the result is a fraction and a whole number, the part of the revolution of the crank after turning the whole number by multiplying is suitable for numbers to the numerator and denominator of the fraction. This makes the denominator of the fraction 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
                                        =  in minutes / 540
                                          =  in seconds / 32400

Compound Indexing Head 

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 which engages with one of the whole circle of the index place from the back. For indexing first, the crankpin 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 rotating the plate together with the index crank forward or backward through the calculated number of spaces of another hole circle, the lock pin is engaged. The net movements are the sum of the movement, therefore,

[40/N = n/N1 + n2/N2]

Where  N is the number of divisions required
            N1 is the hole circle used by the crankpin
           N2 is hole circle used by the lock pin
           n1 is space moved by the crankpin in N1 hole circle
           n2 is the spaces moved by the plate and the crankpin in N2 hole circle.

Solving a problem on Indexing Head

Q 1. Find out the index movement required to mill a hexagonal Bolt by direct indexing. The rapid index plate has 24 holes.


Number of holes to be moved = 24/N =24/6=4
Therefore after machining one side of the bolt, the index plate has to move by 4 holes for the next face to the machine.

Q 2. Set the dividing head to mill 30 teeth on spur wheel blank by simple indexing.


Index Crank movement = 40/N = 40/30 = 4/3 = 4/3 * 7/7 =1+(7/21) 1 Full turn and 7 holes in 21 holes circle of the index plate.


Why indexing head is used in milling machine?

The indexing head is a crucial tool in milling machines, attached to the spindle, enabling precise rotation of the workpiece at various angles. It allows machining at different angles, creating complex shapes and contours not achievable with conventional methods. The head also facilitates multiple cuts without manual repositioning, saving time and effort, while ensuring symmetrical features like gear teeth or flutes. Skilled machinists value its role in achieving high-quality milling results efficiently and cost-effectively.

How dividing head works?

Dividing heads are indispensable tools for machinists and engineers who require precise angled cuts or rotations. They work alongside milling machines or similar tools to divide workpieces equally or rotate them to specific angles. The key components of dividing heads are a spindle and a worm gear. The spindle can be rotated to any angle which is mounted on a swiveling base. The worm gear meshes with a worm wheel attached to the spindle. Turning the worm gear rotates the spindle, achieving the desired division or rotation of the workpiece. To use a dividing head, the workpiece is mounted on the spindle and secured. The operator sets the worm gear to the desired ratio, determining the spindle’s rotations per turn of the worm gear. As the worm gear is turned, the spindle rotates, accomplishing the desired angle division or rotation. Dividing heads are versatile and reliable, providing accurate results, which is why they are a valuable addition to any workshop. They are also used in manufacturing some exterior car panels.

How much does indexing head machining cost?

The cost of indexing head machining varies based on material type, project complexity, and service provider location. Prices range from a few hundred to several thousand dollars. However, don’t solely focus on cost; consider experience, reputation, and work quality. Choose a provider with a proven track record of delivering high-quality results and excellent customer service.


Throughout this article, we have delved deep into the intricacies of indexing heads, exploring the different types, their advantages and disadvantages, and how they are used in a wide range of applications. We have seen how they can be used for everything from cutting gears and splines to drilling holes and milling slots, and how they have revolutionized the world of machining.

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