CNC Rotary Tables

Rotary tables allow the operator to manually index an axis of rotation to any angle with less than one revolution. They are used primarily in 3-axis milling and engraving machines.

A rotary table with a rotating work surface typically fixes the Z-axis, while the X and Y axes can be rotated by means of turrets, or by hand if not on turntable. The non-rotating Z axis is often used for machining operations such as drilling, or recessing which need accuracy but no rotational movement about that axis. Rotary tables may have one or more axes mounted on a circular worktable called a "turntable".

The Rotary Table is a complex tool and requires practice. It is an advantage to have the table on a milling machine, as this allows the most accuracy. The operator needs to hold the rotary in one hand while turning the turret or turntable with their other hand. A rotary table can be mounted to a workbench or table using clamps.

A rotary table is used to position the spindle of a milling machine at specific angles on a surface plate of fixed (and sometimes known) dimensions. This is often used to hold several parts in place for milling operations, but it also permits making measurements off of a common surface plate, without changing reference marks. A rotary table is also useful for other operations, such as drilling and reaming, when the spindle must be held at specific angles to the surface plate.

Some rotary tables have a clamping device on the worktable that allows it to hold cylindrical objects in place. These are used mostly to position drill bits within a hole. This can be useful for making holes of precise diameter, or of making deep slots in a part that would otherwise not support its own weight. 

Rotary tables can be mounted alone or they may come with a milling machine-like table mounted on the same mounting plate (this combination is usually called an X-Y mill). The plate is usually of thick, rough iron or steel. The surface is typically two flat surfaces with a z-axis running between them. Each side has a fixed angle and is usually about in diameter. The unevenness of the surfaces is necessary for both the accuracy and the smooth wear of the milling cutter; this allows it to be ground on the base of each side within the tolerances allowable. Black oxide can be used to improve its appearance and increase its longevity. It also improves the non-contact nature of the surface contact between machine tool and workpiece.

The X-axis is usually a cast iron tube as it is strong enough to support the workpiece and machine tool. The length of such X-axis is usually known, but it may also have a scale readout along its length.

The Y-axis is paired with a rotary table. It rarely has a scale, though some do have small markings on their surface to indicate the angle with which they are mounted on the table. Where they are in popular use, they are often found connected by heavy chain and pulleys as a result of their weight.

To operate a rotary table, the user places the workpiece or tool on the table, and then uses a handwheel to control the X-axis of the spindle. Typical handwheels are used for this purpose, often with a flange to protect them from wear. Such flanges also make them easily accessible for maintenance or replacement. 

In many cases there are two axis so each axis is controlled by two handwheels. Often there are other controls mounted in such X-Y milling machines; knobs or buttons on top of the tool's head can be rotated to alter settings of machine parameters such as speed and direction.

The Z-axis of a rotary table (the table's surface) is generally fixed and not adjustable. The Z-axis can be used for drilling holes through the workpiece, or for clamping parts of a workpiece together. A drill placed in the spindle can rotate it vertically at any angle relative to the surface plate. 

When using a rotary table, it is necessary to decide what part of the workpiece is important, and that part should be placed on top of the table. When using an X-Y milling machine with a rotary table, it is necessary to decide what part of the table is important; whether it's horizontal or vertical motion relative to the machine tool or vice versa.

The importance of the X-Y motion to the machine tool is determined by its own motion; specifically, whether the spindle is mounted on a ballscrew (which can be moved in small steps) or on conventional stepper motors (whose motion is dependent on their position). The motor is controlled by a canned cycle, and so other features like dynamic acceleration/deceleration are also affected. The result of this decision is that it must be adjusted carefully.

In some cases, machines have rotary tables and X-Y mills that act as removable modules. An example of this would be an XY mill with a rotary table mounted beside it on the same mounting plate. This allows the use of both setups at the same time, with little or no adjustment.

The main disadvantage of a conventional rotary table is the extra weight of a two-axis system that must be moved constantly when making adjustments to the spindle's position. This can require an additional machine to control it; this is called "toolchanger" and was commonly used in past years. The toolchanger would allow gripping either the workpiece or a cutter itself, and could rotate it into place before returning it to its original position for another cut. The toolchanger could also be used for other operations such as milling, drilling, tapping and reaming. While this may be a significant time saver, the low-latency nature of the tables makes it difficult to perform many of these tasks precisely.

The main advantage of a conventional rotary table is that it can be integrated with a CNC milling machine, enabling real-time input on the same surface. If a milling machine has an X-Y table and XY stage, then it is possible to use both at once. This allows the use of one machine for all types of tasks, something not possible on most rotary tables due to their design.

One of the ways in which a rotary table is used is to make strongeners for many types of mechanical parts. These parts need to have their shape secured by the machine tool, but their strength should be maintained during cutting. The design of such a part often involves deliberate undercuts at critical points, which weaken the material in these regions. The table can then be set up to cut from different directions and produce matching parts; once done so, the part will be un-weakened and not subject to racking during actual machining. 

Artists often use similar methods for producing reliefs (such as those found in marble sculpture) as well as more everyday shapes like lettering or patterns in wood or metal.

Conclusion: A rotary table is a specialised machine tool used along with a machine tool generally known as a milling machine. The table is mounted on the X-Y axes and rotates on X-Z axis with the help of a motor.

X-axis is straight, it may have scales on it to be used for measurements and setting of spindle position. Y axis has rotary table which can move either in clockwise or anticlockwise direction. It can also be moved up and down. Y axis has ball screws fixed in them to control the movement of rotary table.