Art-Rotary Actuators Part 2
Precision work positioning machines that are used in metalworking are known as rotary stages. This machine allows the operator to cut or drill work at exact intervals around a fixed axis; the axis being usually vertical or horizontal. Some of the rotary tables enable the plate indexing for indexing operations, and others can be fitted by dividing plates which allow for the usual work positioning at divisions for, which indexing plates cannot be found. A dividing head is the more appropriate term to give this type of rotary fixture. It can also be references as an indexing head. rotary tables can be manually operated or operated by a machine. There is the CNC, computer numerical control machines available that supplies the fourth axis to CNC milling machines.
Rotary tables consist of a solid base that provides for clamping onto a fixture, table or workspace. A work piece is clamped on the actual table. This disc can be rotated freely for indexing or under the control of a hand-wheel or a worm, where the worm wheel part being integrated into the actual table. Reaction compensating duplex worms drives high precision rotary actuators. The ratio that is between the table and the worm is usually 40:1, 90:1 or 72:1. This is not constant as it can be any ratio that can exactly divide into 360 degrees which is to aid for easy use when there is the availability of indexing plates. Rotary tables can be positioned with the use of a vernier scale and a graduated dial. This ensures that the work is placed with immense accuracy. A hole to admit a Morse taper fixture or center is machined in the table.
Rotary tables have a large number of uses. However, to understand them, there has to be the knowledge of how it is arranged or placed and how it generally works. Rotary tables are usually mounted ‘flat’ where the rotary tables tend to rotate around an axis that is vertical, in the same plane as a vertical milling machine cutter. Mounting rotary tables at its own end or placing the table flat on an angle plate that is 90 degrees in that it will rotate about an axis that is horizontal is also an alternative. A tailstock is an option in this kind of configuration to hold the work-piece between the centers. Mounting the work-piece accurately at the centre of the axis of rotary tables that are subsequently at the center of the cutting tool axis is an option on a secondary table.
All these three axes are therefore coaxial. Offsetting the cutter in a Y or X direction in the secondary table is possible, to set the desired distance of the cutter from the center of the work piece at this particular point. Rotary indexers could be used to drill equal holes in distance on a circular projection, to mill helixes, cutting complicated curves, machine spanner flats on a bolt and creating large in diameter holes by milling in, a tool-path that is circular on milling machines that are small and may lack the power to drive huge twist drills.