Rotary table
Encyclopedia
Horizontal plane
In geometry, physics, astronomy, geography, and related sciences, a plane is said to be horizontal at a given point if it is perpendicular to the gradient of the gravity field at that point— in other words, if apparent gravity makes a plumb bob hang perpendicular to the plane at that point.In...
or vertical
Vertical direction
In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i.e., with the direction of the gravitational force at that point...
) 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
Indexing head
An indexing head, also known as a dividing head or spiral head, is a specialized tool that allows a workpiece to be circularly indexed; that is, easily and precisely rotated to preset angles or circular divisions...
).
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. High precision tables are driven by backlash compensating duplex wormDuplex worm
Contrary to standard toothing of worm gear sets, the two flanks of duplex or dual lead worms and wheels are manufactured with slightly different modules and/or diameter quotients....
s.
The ratio between worm and table is generally 40:1, 72:1 or 90:1 but may be any ratio that can be easily divided exactly into 360°. This is for ease of use when indexing plates are available. A graduated dial and, often, a vernier scale
Vernier scale
A vernier scale is an additional scale which allows a distance or angle measurement to be read more precisely than directly reading a uniformly-divided straight or circular measurement scale...
enable the operator to position the table, and thus the work affixed to it with great accuracy.
A through hole is usually machined into the table. Most commonly, this hole is machined to admit a Morse taper center or fixture.
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 machineMilling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...
. An alternate setup is to mount the rotary table on its end (or mount it "flat" on a 90° angle plate
Angle plate
An angle plate is a work holding device used as a fixture in metalworking.The angle plate is made from high quality material that has been stabilized to prevent further movement or distortion...
), so that it rotates about a horizontal axis. In this configuration a tailstock can also be used, thus holding the workpiece "between centers
Lathe center
A lathe center, often shortened to center, is a tool that has been ground to a point as to accurately position a workpiece about an axis...
."
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
Coaxial
In geometry, coaxial means that two or more forms share a common axis; it is the three-dimensional linear analogue of concentric.Coaxial cable, as a common example, has a wire conductor in the centre a circumferential outer conductor and an insulating medium called the dielectric separating...
. 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
Concentric
Concentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric to one another...
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 contours.
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 create large-diameter holes, via milling in a circular toolpath, on small milling machines that don't have the power to drive large twist drills (>0.500"/>13 mm)
- To mill helixHelixA helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...
es - To cut complex curves (with proper setup)
- to cut straight lines at any angle
- to cut arcs
- with the addition of a compound table on top of the rotary table, the user can move the center of rotation to anywhere on the part being cut. This enables an arc to be cut at any place on the part.
Additionally, if converted to stepper motor
Stepper motor
A stepper motor is a brushless, electric motor that can divide a full rotation into a large number of steps. The motor's position can be controlled precisely without any feedback mechanism , as long as the motor is carefully sized to the application...
operation, with a CNC milling machine and a tailstock
Tailstock
thumb|Tailstock used for drillingA tailstock, also known as a foot stock, is a device often used as part of an engineering lathe, wood-turning lathe, or used in conjunction with a rotary table on a milling machine....
, a rotary table allows many parts to be made on a mill that otherwise would require a lathe
Lathe
A lathe is a machine tool which rotates the workpiece on its axis to perform various operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the workpiece to create an object which has symmetry about an axis of rotation.Lathes are used in woodturning,...
.