Rotary table
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A rotary table is a precision work positioning device used in metalworking. It enables the operator to drill or cut work at exact intervals around a fixed (usually horizontal or vertical) axis. Some rotary tables allow the use of index plates for indexing operations, and some can also be fitted with dividing plates that enable regular work positioning at divisions for which indexing plates are not available. A rotary fixture used in this fashion is more appropriately called a dividing head (indexing head).
[edit] Construction
The table shown is a manually operated type. Powered tables under the control of CNC machines are now available, and provide a fourth axis to CNC milling machines.
Rotary tables are made with a solid base, which has provision for clamping onto another table or fixture. The actual table is a precision-machined disc to which the work piece is clamped (T slots are generally provided for this purpose). This disc can rotate freely, for indexing, or under the control of a worm (handwheel), with the worm wheel portion being made part of the actual table.
The ratio between worm and table is generally 40:1, but may be any ratio that can be easily divided into 360°. This is for ease of use when indexing plates are available. A graduated dial and, often, a vernier scale enable the operator to position the table, and thus the work affixed to it with great accuracy.
A center hole is usually machined into the table. Most commonly, this hole is machined to admit a Morse taper center or fixture.
[edit] Use
Rotary tables are most commonly mounted "flat" with the table rotating around a vertical axis, in the same plane as the cutter of a vertical milling machine. If the rotary table can be mounted on its end, so that it rotates about a horizontal axis, a tailstock can be used to hold the workpiece "between centers."
With the table mounted on a secondary table, the workpiece is accurately centered around the rotary table's axis, which in turn is centered around the cutting tool's axis. All three axes are thus coaxial. From this point, the secondary table can be offset in either the X or Y direction to set the cutter the desired distance from the workpiece's center. This allows concentric machining operations on the workpiece. Placing the workpiece eccentrically a set distance from the center permits more complex curves to be cut. As with other setups on a vertical mill, the milling operation can be either drilling a series of concentric, and possibly equidistant holes, or face or end milling either circular or semicircular shapes and conours.
A rotary table can be used:
- To machine spanner flats on a bolt
- To drill equidistant holes on a circular flange
- To cut a round piece with a protruding tang
- To cut complex curves (with proper setup)
See also:
 Metalworking:
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Angle plate | Chuck | Collet | Fixture | Indexing head | Lathe center | Machine taper | Magnetic base | Mandrel | Rotary table | Wiggler |
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