Indexing tables are vital to the manufacturing and assembly processes in countless facilities around the world. They are incredibly useful and efficient machines in automation applications, and can help to complete certain tasks faster than a person alone or in some applications, most other machines could. Indexing tables need to be incredibly accurate, precise and consistent to perform their task in a satisfactory fashion, making them quite sophisticated and technologically advanced.
What is an Indexing Table?
An indexing table is a machine tool positioning device. Also sometimes called a rotary indexing table or just rotary table, they repeat the process of rotating or “indexing” around an axis, stopping, dwelling while an operation is performed, then indexing again so the process can be repeated.
The operation being referred to during the dwell is often the machining or assembly of relatively small parts or objects on an assembly line. Most indexing tables are made up of a circular steel plate, one or more spindles, a drive system, encoders, sensors, controllers and slots or mounting holes to hold components for operations to be performed on. Depending on the type of indexing table, the table may have fixed indexing angles or adjustable angles.
Parameters used to determine which indexing table is best for which application include:
- Mass Moment of Inertia
- Allowable Backlash
Mass Moment of Inertia refers to the amount of torque needed to
cause any given angular acceleration.
Repeatability refers to the consistency of the table’s indexing.
Accuracy refers to how accurate to the measured index the actual index was.
Allowable Backlash refers to the allowable recoil after indexing.
Other indexing table specifications include maximum indexing increment, the table diameter, and the maximum axial and radial loads. Different components on the table can determine its characteristics, for example, the bearings supporting the table determine the load capacity and accuracy. Specifically, angular contact bearings are more expensive than ball bearings, but they provide better load capacity and axial stiffness.
Different indexing tables have different features, all of them suited to different applications and environments. Some table surfaces can be raised and lowered at a controlled angle, and some have more than one rotating work surface. Some work in tandem with computer numerically controlled (CNC) devices, giving them greater accuracy and consistency. There are even four and five axis tables, both allowing X, Y and Z axis motion, but the fourth axis being rotation along the X axis and the fifth being rotation along the Y axis.
Types of Indexing Tables
There are several types of indexing tables, all with the same general purpose but driven by different power sources and with slightly different characteristics based on the different power sources.
Pneumatic indexing tables are powered by one or more pneumatic cylinders. Each cylinder represents an index, each one moving the table one set angular displacement. During the return stroke of the cylinder, the table shouldn’t move back to its previous position, so a pawl is used to lock the table in place. The pawls can also be adjusted to change the number of indexes. Pneumatic indexing tables are best suited for small and medium loads.
Electrically Powered Indexing
Electrically powered indexing tables are the most popular type of table and have many variations. Two popular variations include mechanical cam drives and servo tables. The cam indexers are inexpensive and capable of precision moves, but only index to set angles. Servo tables are driven by a servo motor, which allows for indexing to adjustable angles that are not always the same. Electrically powered indexing tables are often capable of faster indexing and can handle heavier loads.
Some less common types of indexing tables include hydraulically driven tables and manually-actuated tables. Hydraulic indexing tables are driven by pressurized hydraulic fluid that transfers pressure to rotational kinetic energy of the table. Manually-actuated tables are somewhat self explanatory, requiring an operator to use a hand crank to index the table, or requiring the operator to loosen, turn and adjust the table by hand.
With all of the above driving mechanisms, indexing tables also have different types of configurations. These different configurations all have certain strengths and weaknesses, and are therefore more suited for specific purposes.
Cam Index Drives
Cam index drives involve, as the name suggests, cams that drive the table. Their design eliminates the reversal of the roller follower direction and prevents the tendency to overheat and inflict tear on the cam surfaces. They are best used when high speed indexing is needed, being capable of over 1000 indexes per minute. They also have high torque and load capabilities, but are not appropriate for a large amount of stations to index to, the ideal number of stations being between 1 and 8.
Ring Index Drives
Ring index drives are convenient when trying to reduce the footprint of machinery around the indexing table. They have large through-holes that can accommodate different types of automated machinery and equipment, including electrical wiring and air or hydraulic lines. Feeding this equipment through the center through-hole frees up the area around the table for other equipment. These index drives are also well suited for automatic assembly machinery with a large number of stations.
Roller Gear Index Drives
Roller gear index drives also offer through-hole capability, as well as motion flexibility and a large range of stations that can be indexed to, from 2 to 24. They are suited well to compact and low profile situations, and are often used when medium to high torque and right angle shaft orientation are required. They are also used in harsh environments that need torque limiting protection.
The engineering and intricate design that goes into indexing tables is quite impressive, and they perform a myriad of tasks in different applications. Some applications include assembly, equipment positioning, automation, inspection and machining, and many more.
Have questions about your indexing table application? reach back to us, we’re happy to help!
In the meantime you can get the guide below to help with your indexing table purchase decision.