1. Indexing, Helical and CAM Milling
By: Rahul Vasava ( )
Sandip Vasava ( )
Vedant Tailor ( )
Guided by: Bhavesh Modi

2. Indexing
Indexing is the operation to divide the circumference of workpiece into equally spaced divisions when milling gear teeth, squares, hexagons, and octagons.
Indexing is accomplished using a special attachment known as dividing head or index head

3. Indexing Methods Indexing Methods
The choice of any method depends upon the number
of divisions required.
Direct
Simple
Angular
Differential

4. Direct Indexing Simplest form of indexing
Performed by disengaging worm shaft from worm wheel by means of eccentric device in dividing head
Spring-loaded tongue lock engages numbered slots in index plate
Used for quick indexing of workpiece when cutting flutes, hexagons, squares, etc.

5. Direct indexing plate usually contains three sets of hole circles or slots: 24, 30, and 36
Number of divisions possible to index limited to numbers that are factors of 24
No. of holes to be moved = 24/N
Where, N = number of divisions required

6. Simple Indexing
Work positioned by means of crank, index plate, and sector arms
Worm attached to crank must be engaged with worm wheel on dividing head spindle
40 teeth on worm wheel
One complete turn on index crank cause spindle and work to rotate one-fortieth of a turn (ratio of 40:1)

7. Calculating the indexing or number of turns of crank for most divisions, simply divide 40 by number of divisions to be cut.
Example : The indexing required to cut eight flutes:

8. Angular Indexing Setup for simple indexing may be used
Must calculate indexing with angular distance between divisions instead number of divisions
One complete turn of index crank turns work 1/40 of a turn
1/40 of 360º equals 9 degrees

9. Example : Calculate indexing for 45º
5 complete turns

10. Differential Indexing
Used when 40/N cannot be reduced to a factor of one of the available hole circles
Index plate must be revolved either forward or backward part of a turn while index crank turned to attain proper spacing (indexing)
Change of rotation effected by idler gear or gears in gear train

11. Example: Assume index crank has to be rotated 1/9th of a turn and only 8-hole circle
Crank moved 1/9th, index pin contacts plate at spot before first hole
Exact position would be the difference between 1/8th and 1/9th of a revolution of the crank
Since there is no hole at this point, it is necessary to cause plate to rotate backward by means of change gears one-seventy-second of a turn of pin will engage in hole.

12. Helical Milling
Helical milling produces helical flutes or grooves on the periphery of a cylindrical or conical work piece. This is performed by swiveling the table to the required helix angle, then rotating and feeding the work piece against revolving cutting edges of milling cutter. Helical gears and drills and reamers are made by this operation.
Performed on universal milling machine by gearing dividing head through worm shaft to lead screw of milling machine.

13. Helix : It is a theoretical curve or path whose tangents are inclined at a constant angle on the axis of the cylinder.
 A helix angle is the angle between any helix and an axial line on its right, circular cylinder or cone.

14. Lead of the helix varies with :
Lead : The distance between two consecutive intersection of a helix by a straight generator of the cylinder on which it lies.
Lead of the helix varies with :
Diameter of work
Angle of helix

15. Determining the Helix angle
Helix angle : The acute angle between the
tangent to a helix and the straight
generator of the cylinder on which it lies. tan

16. To what angle must the milling machine table be swiveled to cut a helix having a lead of 250 mm on piece of work 40 mm in diameter?

17. Cam Milling Operation
The operation cam milling is used to produce the cam on milling machine. In this operation cam blank is mounted at the end of the dividing head spindle and the end mill is held in the vertical milling attachment
 Cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa. It is often a part of a rotating wheel(e.g. an eccentric wheel) or shaft (e.g. a cylinder with an irregular shape) that strikes a lever at one or more points on its circular path.

18. The cam can be seen as a device that rotates from circular to reciprocating (or sometimes oscillating) motion. A common example is the camshaft of an automobile, which takes the rotary motion of the engine and translates it into the reciprocating motion necessary to operate the intake and exhaust valves of the cylinders.

19. Types of cam milling operations:
Plate cam
Cylindrical cam
Face cam
Linear cam

20. Plate cam:
The most commonly used cam is the plate cam (also disc cam or radial cam) which is cut out of a piece of flat metal or plate. Here, the follower moves in a plane perpendicular to the axis of rotation of the camshaft.
Several key terms are relevant in such a construction of plate cams: base circle, prime circle (with radius equal to the sum of the follower radius and the base circle radius), pitch curve which is the radial curve traced out by applying the radial displacements away from the prime circle across all angles, and the lobe separation angle (LSA - the angle between two adjacent intake and exhaust cam lobes).