Indexing Operations on a Milling Machine

Machine technology, manufacturing operations / indexing operations on a milling machine are used to divide cylindrical materials into equal parts. For example: gear manufacturing on a universal milling machine using traditional methods. There are two methods for this: simple indexing and differential (compound) indexing. In this article, we’ll cover topics such as simple indexing calculation and differential indexing calculation.

Operations such as linear indexing, cutting grooves, cutting rack teeth, and forming polygons on a workpiece in a milling machine are defined as indexing operations. The auxiliary attachments that perform these tasks are called indexing attachments.

Circular (Radial) Indexing

Operations such as cutting grooves and holes at certain angles around the circumference of cylindrical parts, or forming polygons, are called Circular Indexing. They’re performed with devices such as a simple indexing attachment, an indexing center, or a dividing head.

Linear Indexing

Operations such as making steel rulers, manufacturing rack gears, and cutting consecutive holes or grooves are performed with surface (linear) indexing. This is done with a linear indexing device.

Indexing Methods Used in Milling

Indexing operations performed on milling machines are named according to the auxiliary device used.

1- Direct Indexing

Done with simple indexing attachments. It covers indexing operations that can be done directly, such as triangles, squares, hexagons, octagons…

2- Indirect Indexing

These are indexing operations performed using the dividing head’s index plates for divisions that cannot be done with simple indexing devices.

Indexing Devices Used in Milling and Their Parts

1- Simple Indexing Attachment

These devices allow direct indexing operations to be performed on workpieces. Indexing is performed via perforated discs or notched discs mounted at the back of the devices. The lever piece engaging with the perforated discs allows the division to be made. Simple indexing devices are mounted to the milling table with a “T”-bolt, nut, and stud. A simple indexing attachment consists of a body, a spindle, a perforated or notched disc, and a chuck or center.

2- Vertical Indexing Attachment

3- Angular Indexing Attachment

In circular indexing operations, a different indexing method is applied when the steps (intervals) between divisions aren’t equal. It’s used when the angular values between divisions are in different steps. This process is called Angular Indexing. Since vertical indexing attachments have an angular index flange around their circumference, indexing can be done without needing to calculate anything. On those with a perforated chuck, calculation must be done. A T-bolt and nut attach it to the table. It consists of a body, a turning lever, and a table. It’s attached to grooves on the parts with the help of a T-slot shoe.

4- Linear Indexing Attachment

Used for rack gears and rulers, and for holes to be drilled at equal intervals. A linear indexing attachment consists of a turning lever, perforated drum gears, a piece for mounting to the machine table, and a body. A gear is fitted onto the table spindle, and the indexing attachment is mounted. Indexing is performed by controlling the table spindle from the attachment.

5-Universal Indexing Attachment (Dividing Head)

This is the attachment used for indirect indexing operations. It’s also used for divisions in gear cutting that cannot be done with a simple indexing attachment.

A dividing head consists of parts such as: a body, a perforated chuck, a turning lever, a sector arm, the perforated chuck’s tailstock spindle, the dividing head’s tailstock spindle, and a chuck. It’s mounted to the machine table with a “T” nut, a stud, and a nut. Gears and change gears are needed when differential (compound) indexing is to be performed.

Motion transmission in the dividing head is as shown in the figure below. Motion transmission is achieved by connecting gears between the perforated chuck’s tailstock spindle and the dividing head’s tailstock spindle.

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Indexing with a Dividing Head

You can find detailed explanations on this topic through the links below:

1- Circular (Radial) Indexing in Milling – Simple and Differential Indexing

2- Performing Linear Indexing in Milling – Ruler Graduation and Rack Gear Manufacturing

Rules to Follow When Performing Indexing Operations on a Milling Machine

1. An indexing device suitable for the type of indexing operation must be selected.
2. A cutter suitable for the indexing operation must be selected.
3. A clamping method suitable for the job must be selected.
4. The turning ratio (N) for the indexing device must be calculated according to the type of division, and the perforated chuck or notch must be selected according to the number of holes to be skipped.
5. The turning lever’s position and sector arm settings must be made, and the clamping screws must be tightened.
6. The accuracy of the turning amount and the sector arm opening must be checked.
7. Before starting the cutting operation, the machine should be set up by calculating the spindle speed according to the feed rate, depth of cut, cutter diameter, and cutting speed.
8. During hole-skipping, the current hole should be counted carefully before skipping.
9. The turning lever should always be turned in the same direction, and backlash should always be taken up in the same direction. 10. If differential (compound) indexing is to be performed, the chuck locking screw’s locking pin should be open.
10. After the turning operation, the turning lever’s pin should be inserted firmly into the hole

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