What is indexing?

Short Answer:

Indexing is a process used in machining, especially on a milling machine, to divide the workpiece into equal parts or angles accurately. It is mainly performed using an indexing head or dividing head, which allows the workpiece to be rotated by a precise amount for each cut. This operation helps in making gear teeth, hexagonal bolts, and other equally spaced shapes.

In simple terms, indexing helps in rotating the job by a specific angle or fraction of a turn for cutting uniform divisions. It ensures that each section of the workpiece is cut equally, maintaining accuracy and uniformity in the final product.

Detailed Explanation :

Indexing

Indexing is a very important machining operation used to accurately divide the circumference of a workpiece into equal parts. It is most commonly carried out on a milling machine with the help of an indexing head (dividing head). The main purpose of indexing is to rotate the workpiece by a precise angle between successive cuts. This method is essential for operations such as gear cutting, fluting of drills, cutting splines, and machining polygonal shapes like squares, hexagons, and octagons.

The indexing process ensures that every division or tooth on a gear or similar component is spaced perfectly. Without proper indexing, uneven cutting or irregular spacing may occur, affecting both the function and appearance of the finished product. The indexing head makes it possible to rotate the job through a pre-calculated angle each time a cut is made, thus maintaining uniformity and precision.

Construction of Indexing Head

An indexing head, also known as a dividing head, consists of several key parts:

  1. Spindle: Holds the workpiece or chuck.
  2. Index plate: A circular plate with several holes arranged in concentric circles for indexing.
  3. Crank handle: Used to rotate the index plate and spindle.
  4. Worm and worm gear: Provides a precise rotational movement of the spindle. Usually, a 40:1 ratio is maintained, meaning one full crank rotation turns the spindle by 1/40 of a revolution.
  5. Sector arms: Adjustable arms that help in counting holes accurately during indexing.

These components together allow the machinist to divide the workpiece accurately according to the desired number of divisions or angular spacing.

Working Principle of Indexing

The basic working principle of indexing is to rotate the workpiece by a definite fraction of a full revolution for each cut. When the crank of the dividing head is turned, the worm rotates, which in turn rotates the worm gear connected to the spindle holding the workpiece. The number of crank rotations needed for one complete revolution of the spindle depends on the gear ratio (usually 40:1).

For example, to divide the workpiece into 8 equal parts, the workpiece must be rotated by 1/8 of a full revolution between cuts. Using the 40:1 ratio, the crank must be rotated by 5 full turns (since 40 ÷ 8 = 5). In this way, each division is equal and precise.

Types of Indexing

  1. Simple Indexing:
    This is the most common and simplest type. It uses the basic worm and gear mechanism with the formula:
    Crank rotation = 40 / Number of divisions.
    It is suitable for divisions like 2, 3, 4, 6, 8, etc.
  2. Compound Indexing:
    Used when the required divisions cannot be obtained directly by simple indexing. It involves rotating the crank by a combination of hole circles.
  3. Differential Indexing:
    Used for very large or uncommon divisions. It uses an additional gear train between the spindle and index plate to make small adjustments during rotation.
  4. Angular Indexing:
    Used when the workpiece needs to be rotated through a specific angle instead of equal parts.
    Formula: Crank rotation = (40 × Angle) / 360.
  5. Direct Indexing:
    The spindle is directly rotated by disengaging the worm gear. This is used for small divisions like 2, 3, 4, 6, 8, 12, and 24.

Applications of Indexing

  • Gear cutting: To cut gear teeth equally spaced around the circumference.
  • Fluting of milling cutters or drills: Produces equally spaced grooves along the workpiece.
  • Machining polygons: Helps in making hexagonal, square, or octagonal shapes.
  • Cutting splines and keyways: Ensures proper spacing for torque transmission.
  • Drilling equally spaced holes: Used in components like flanges or discs.

Advantages of Indexing

  1. Provides high accuracy and uniformity in divided parts.
  2. Makes complex shapes like gears and polygons easy to manufacture.
  3. Increases the precision and quality of machining work.
  4. Reduces chances of manual error in spacing or angular division.
  5. Useful for both mass production and tool-making applications.

Precautions in Indexing

  • The index plate must be properly locked before each cut.
  • The workpiece should be rigidly clamped to avoid movement.
  • Accurate counting of holes in the index plate is necessary.
  • Backlash in the worm gear should be adjusted to prevent error.
  • Always rotate the crank in one direction to maintain uniform accuracy.
Conclusion

Indexing is an essential machining process that ensures equal and precise division of a workpiece into the required number of parts or angles. It plays a major role in the manufacturing of gears, splines, and other symmetrical components. With different types of indexing methods available, machinists can perform both simple and complex operations accurately. Therefore, indexing helps in achieving high-quality, consistent, and precise machining results in various manufacturing applications.