Rotary tables are precision work positioning devices that are very widely used for metalworking activities such as drilling and cutting. The workpiece is fixed in position so that the operator can work on it at precise intervals along the horizontal or vertical axis. In that respect, rotary tables serve two functions. When drilling a metal piece, the table provides the rotary motion to the master bushing and applies torque to the drill string.
In some cases, rotary tables allow indexing processes through the use of index plates, while in others by having dividing plates that allow workpieces to be positioned at regular intervals in the same way that index plates allow. Rotary tables derive their motion from independent electric motors or diesel mechanical drives. As it turns, the bit turns with it. It is commonly known as a dividing head when used to make allowances for regular indexing of workpieces.
How They are Constructed
There are numerous rotary table solutions in the market at the moment, predominantly direct drive and mechanical gear transmission (worm gear, spiroid gear) type. Lately, there has been a new trend in hybrid transmission combining different types of transmission drives.
The image above shows a rotary table used for CNC machines. CNC machine rotary tables are either manually operated or powered and provide an additional axis when working with milling machines. A typical rotary table consists of a solid base that is able to clamp or slot into fixtures and other tables. At the surface is a precision-machined disk (with T slots provided) where the workpiece sits.
Table disks can rotate freely during indexing operations or with the use of handwheels if they are part of such tables. For high-precision works, it is recommended that table disks are driven by duplex worms that compensate for backlash. The recommended ratio between a worm gear and table is about 40:1, 72:1 or 90:1, but other formations may exist. However, with indexing plates, the ratio should be such that it is divisible by 360.
Some tables include graduated dials to enable accurate table and work positioning. Additionally, they have through holes machined into them to accommodate fixtures or Morse taper centers.
Applications of Rotary Tables
As with vertical milling machine cutters, rotary tables will most likely be mounted flat to rotate about the vertical axis. In other cases, they are mounted vertically on some angle plate or on the end to rotate about the horizontal axis. Tailstocks help to hold workpieces in place if tables rotate about the horizontal axis. In other instances, rotary tables are mounted on secondary tables, but the workpiece has to be mounted on it and centered along the axis of the cutting tool in what is called a coaxial configuration. Secondary tables can be offset in the X or Y axis to align the cutter with the cutter or place it appropriately for concentric machine operations. A workpiece should be placed eccentrically at some distance from the center allows more sophisticated machining operations. In summary, rotary tables are used in the following:
- Machining spanner flats for bolts
- Drilling circular flanges with equidistant holes
- Cutting off protruding tang from round pieces
- Milling in circular toolpaths to increase hole diameters for smaller milling machines
- Helix milling
- Cutting of complex contours on workpieces
- Cutting straight lines along any axis
- Cutting of arcs
- Cutting out circular pieces out of workpieces
Rotary tables, when combined with compound tables, allow flexibility to move workpieces around to different centers of rotation. That way, arcs can be cut at any point in the workpiece. Rotary tables also enable some lathe operations such as making multiple parts to be machined and milled. That is achieved by stepper motor operation that includes a tailstock and a milling machine.
Rotary tables can be found in machining centers, tapping centers and special purpose machines to help operators with several workloads. Many operations such as automobile parts machining, IT components and auto-transfer lines rely to a large extent on them. They are loved for their ease of installation, great features such as lightweight, high precision and compactness. There are many sources where you can purchase rotary tables including online e-commerce platforms, such as Intellidrives.