how does a rotary table work supplier

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).

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 worms.

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 enable the operator to position the table, and thus the work affixed to it with great accuracy.

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. An alternate setup is to mount the rotary table on its end (or mount it "flat" on a 90° angle plate), so that it rotates about a horizontal axis. In this configuration a tailstock can also be used, thus holding the workpiece "between centers."

With the table mounted on a secondary table, the workpiece is accurately centered on the rotary table"s axis, which in turn is centered on 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 contours.

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)

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 operation, with a CNC milling machine and a tailstock, a rotary table allows many parts to be made on a mill that otherwise would require a lathe.

Rotary tables have many applications, including being used in the manufacture and inspection process of important elements in aerospace, automation and scientific industries. The use of rotary tables stretches as far as the film and animation industry, being used to obtain accuracy and precision in filming and photography.

A CNC rotary table is the precision positioning accessory that can provide a reliable 4th axis or even 5th axis for modern machining centers. Utilizing a computer-controlled rotary table can turn the original 3-axis machine tools into 5-axis CNC machines, expanding the accuracy as well as decreasing the costs while performing complex machining operations at one time.

A CNC rotary table is the precision positioning accessory that can provide reliable 4 or even 5 axis cutting operation capabilities for modern machining centers. Utilizing it can turn the original 3-axis machine tools into 5-axis CNC machines, expanding the accuracy as well as decreasing the costs while performing complex machining operations.

Rotary tables typically have rigid frames and coatings, and also excellent torque capacity, which makes the small device flexible and effective for a wide variety of turning, milling, drilling, and more metalworking operations. The easy setup and seamless interface allow the operators to easily add the rotary table to fit their 4-axis or 5-axis applications. .

The working principle is similar to the basic rotary tables, which is to support the workpiece by accurately rotating the workpieces on the axis in order to locate the parts for high precision tooling. Under rapid rotation, which is driven by CNC instructions, the cutting tools of larger machine tools or machining centers can remove the material and add the feature to the products at exact intervals. On rotary tables, there are vertical and horizontal axes for various tools to perform these high-performance metalworks. To enhance the accuracy and flexibility, there are models that employ additional dividing plates and come with additonal material handling mechanisms and features.

Since 4-axis and 5-axis machining is increasingly popular today, adding the CNC rotary table as the 4th axis is an ideal solution to easily open up more complex machining options at a lower cost. Due to the arrangement, they are widely also called the 4th or 5th axis or tilt rotary. The 4th axis, which is the rotational operational direction, is added to the original three linear axes which are known as X-axis, Y-axis, Z-axis. In some cases, there are two rotational axes add to the original 3-axis machining center, achieving utmost accuracy as well as effective multiple face cutting to reach the difficult area on the surface. Rotary tables are usually mounted parallel to the ground or the bed, with the platter rotating around the vertical axis, for example with the most common vertical milling machine combination. Sometimes the machining application requires an alternative setup with the table mountet on its end so that it rotates around the horizontlal axis. Often, a tailstock is used in this configuration. Virtually all models today come with a clamping kit to mount it onto the bed of your machine tool.

The function of the high precision rotary table is also to rotate the workpiece so the cutting tool can create the contour we desired out of the workpiece. However, a rotary table with higher precision has the ability to achieve great accuracy just as its name implies. There is also a major misconception between the resolution and the accuracy.

A common example is that if a digital readout displays to four decimal places, then the high precision rotary table must also be capable of achieving the accuracy to that same value. Even though for higher accuracy to be achieved, the resolution has to also be high, but there is no guarantee that the accuracy is going to be high. The accuracy is the concept which is the difference between the actual position and the position measured by a reference measurement device. The feedback mechanism such as the rotary encoder, and the drive mechanism can influence the accuracy of the advanced rotary table.

A CNC rotary table can provide great rigidity for stable machining operations. It consists of the worktable where the metal parts are held, the rigid bearing that withstands the forces and loads during the rotation, the solid base which is used for attaching the rotary table to the machining center or other equipment, the motor, and the CNC system.

The worktable is the tooling surface where the workpieces are machined after accurate positioning. The worm gearing is the core mechanism of the table, which mesh with the steel worm which is submerged in the lubricants. Both the rigid bearings and the worm gears have large diameters. Excellent concentricity is the key to smooth operation, durability, and most importantly, accuracy. Driven by a computer and electric motor, the worktable can position the materials at exact intervals. For more flexible or critical operations, dividing plates can be added to this component.

A CNC system regulates the simultaneous 4-axis motion of the rotary table. The instructions are programmed and transmitted via CAD software, reducing the time for adjustment and monitoring by human workers.

The type and size of the electric motors utilized in can define the router accuracy as well as the efficiency of the device. Servo motor and stepper motor are two typical types that can be divided into more subtypes. The servo motor uses a closed looping variable circuit, the circuit will constantly run to keep the function. The brushes must be replaced every 2000 hours of operation in the servo motor. Compared to stepper motors, servo motors are more efficient in power consumption. On the other hand, the stepper motor has a simpler setup which are the wires that are attached to the driver. The bearing of the stepper motor is the only wearing component. However, the stepper motor consumes a great amount of energy.

There are currently several different types and models available in the industries. Each of them possess its own traits and abilities. Let us take a look at the most common ones other than standard three axis tables

The 4 axis CNC rotary table will process the workpieces by holding them in the same position while the cutting tool performs along the XYZ plane to trim away the unwanted material. In general, a 4 axis model is very versatile equipment that can be used for several different industrial processes such as engraving curved surfaces, continuous cutting, and intermittent cutting. Besides, people can also add other devices such as cam machining, blade machining, and helical grooves to the 4 axes rotary table. Such a feature is simply impossible to achieve with the machining center which has only 3 axes.

Besides the 4 axis ones, there are also 5 axis models. They have the ability to allow the workpiece to be processed automatically from five sides at one time. people usually utilized the 5 axes rotary table in the industries such as the automobile, the aerospace, and the boating industries. The reason that the 5 axes rotary table is commonly used in heavy industries is that the 5 axis machining is an important technique to be used when the components need better intricacy and quick precision. All of these have more than three axes are called the multi-axis rotary table.

The installation method of the precision rotary table can be horizontal, vertical or inverted. When installed horizontally, the workbench surface is in a flat, vertical and horizontal position. When installed vertically, a rotary table is installed so that the surface of it can run up and down. In the reverse layout, itcan be rotated upside down in a horizontal position. The location of the drive of the rotary table can depend on the mount. The drive can be placed on the back, below, on the top or on the side.

When mounted horizontally, the spinning table top drive is positioned above the table floor. When the rotary table is horizontally placed, the side-mounted drive is located on the edge of the table board. The driving mechanism of the rotary table may be manual, electrical, pneumatic, hydraulic or non-driven. For manual revolving workbenches, release the workbenches and manually spin the workbenches with the crank.

Workpieces are gathered and machined through PC and fully programmed instructions. The 5-axis simultaneous operations will be measurably more reliable than products machined via different technologies. Also, the setup is simple and provides an indistinguishable process in every production cycle, the consistency of the quality of the metal products can be ensured under critical control and precision cutting.

Since the metalwork is driven by software, the preferred frameworks can be programmed and adapted by the rotary table. Saving both the cost and the room makes themis the ideal solution for potential users who don’t want to install larger equipment and new machines which may take up a great room for a wide variety of machining applications.

Another benefit is the utmost movements can be completed precisiely and faster. There are more favorable positions, operation angles as well as accessible machining that can be achieved through the technology. The complex operations are suitable for blade, helical grooves production, and other applications required to add complex features or require critical inspection in machining processes like the manufacturing of aerospace, automotive parts, and scientific equipment.

Addding a rotational table saves time because the extra finishing jobs or other sub-operations can also be performed at one time in the machining center.

A rotary table can be used in many applications including manufacturing, inspection, and assembly. Indicators are used, for example, for assembly, manufacturing, and bottling equipment. They typically use a single item in workspaces or move relatively small layouts of items around stations for sequential work or assembly.

In automated assembly machines, the rotary tables implementation is widespread, and choosing the right mechanism is important for both improving efficiency and reducing the cost of this vital component. This guide discusses two common devices for rotating indexing and offers guidance on the right range. There are several ways to get mass mobilization when it comes to the development of rotary indexing tables. Regardless of whether the load or load in centuries of thousands of kgm2 is incredibly light. When choosing a robust rotary index solution that will match or meet your standards, there are several factors to take into account when spinning, elevating, or pushing.

When determining the influencing factors on the postitioning accuracy, the first thing to look at is the mechanical properties of the table itself. A rotary table contains six degrees of freedom. Each of these movements increases the total risk of positioning errors. Usually, a rotary table is driven by a worm gear, which is connected to the motor through a rotary encoder on the back. The position of the table can be determined by the number of pulses transmitted from the encoder to the control device.

The four main sources of error due to the semi-closed position loop are geometric errors, thermal deformation, elasticity, and wear. The sum of these errors is called angular positioning error. To greatly reduce the angular positioning error, the ideal position for installing the angle encoder is on the rotating shaft under test. The angle encoder is installed under the rotary table, and the rotary encoder is installed under the rear motor, the position loop is now considered a closed-loop system.

Precision is a relative term. About a quarter of an inch is great and will meet the accuracy of its application. Others, for example, require micron-level accuracy in measuring and indexing devices. Then, some applications fall within these extreme ranges.

The misunderstanding is that you may have used an inaccurate indexing device and made it accurate by introducing a pin or wedge locking device. These devices increase the complexity and cycle time of use, and when they are used together with a high-precision positioning device, they may cause damage and reduce accuracy.

In the actual test, by selecting specific components, motion index drive, servo rotary indexer, the measurement accuracy is as high as 5-6 microns. These are not the results approved by Motion Index Drives, but the results of customer certification. When starting and stopping large amounts of data, it is important to know how fast it takes to stop the application with large amounts of data.

In a less rigid environment or the presence of higher recoil, a faster start and stop will bring many control problems. When moving masses (whether rotating mass or linear mass), starting and stopping in a system with a backlash of several arc minutes will cause a lot of back and forth movement in the gear system. The result is a force that is difficult or even impossible to calculate. In addition, when the gear head is used in rotating applications, the farther the mass is from the center of rotation, the greater the backlash. In applications with very slow deceleration times, recoil may not be a problem.

Backlash in the positioning process is a big issue – when it comes to the beginning and stopping volumes, it"s crucial to know how quickly you need to avoid the mass of your rotary indexing table applications. In a less rigid system or where there is an increased backlash, quicker start-ups and stops can cause a lot of control issues. When shifting a mass, whether rotary or linear, starting and stopping in a system with several minutes of backlash arc will create a lot of back-and-forth motion within the gearing system. The effect is a power that can be difficult and probably hard to quantify. In comparison, as the gear head is used for rotational applications, the more the mass is from the axis of rotation, the further the backlash is magnified.

The backlash may not be a concern in systems where deceleration times are incredibly long. In the case of cam indexers, there is " Zero Backlash." The cam indexer and rotary table dynamics give an incredibly rigid, highly regulated framework. A modern cam indexer system is capable of withstanding short cycle times with stop times in milliseconds.

So you want to get the smart manufacturing going but are not sure of what to look for in rotary tables. The information provided in this section may be able to help. The primary factor is to determine the mass snapshot of inactivity. This is often overlooked when measuring a rotary table for the machine.

Another significant factor is the size of the workpiece being rotated, including how big it is and how substantial it is. You want your rotary tables to be large enough to handle enormous pieces. This is where tilling rotary tables may become handy so that the pieces can be handled without causing interior harm. They allow the quickening and decelerating of machining at appropriate rates.

The last factor is accuracy, the applications for which, for instance, pivoting a gigantic part to allow welding highlights on it where the individual stop positions can be genuinely free. On an additional note, when choosing direct drive rotary tables, factors that you should consider when selecting a rotary table for your CNC machinery include accuracy, backlash, mass moment of inertia, acceleration and deceleration, speed, and environment.

Indexing system use is commonly possible in automatic assembly machines and the right process is important for both performance maximization and cost reduction.

Cam indexers are an omnipresent tool used for several decades for rotary indexing tables. They are suitable for applications that often index the same angle and need a high degree of accuracy at a relatively low cost. To place the load, a cam indexer uses a mechanical cam. A math curve is pushed onto the cam and provides incredibly smooth and repeatable movement.

Another popular alternative is a fully programmable rotary index table. A rotary table is advantageous in two different situations. Firstly, a versatile movement pattern is important. An example is if two components are running on one computer, each of which requires different index patterns. For incredibly fast placement accompanied by a long period, another condition that matches the servo pointer is. The need to accelerate the camshaft while the cam indexing mechanism was operating before starting the output movement reduced the on-demand cam indexer. Acceleration of the camshaft is possible, but there is a delay before the movement begins. There are realistic restrictions.

With an indexing table, the output rotates as soon as the servo starts moving. This is not difficult for a continuous cam indexer or a zero-backlash servo indexer, but it can also be difficult for an on-demand cam indexer. For applications with high-speed servo indexing, smooth movements are crucial. A zero-backlash preloaded reducer can achieve this. The ideal alternative for correct positioning with high dynamic response would be the zero-backlash reel drive system.

Application parameters, like a moment of inertia, indexing angle, indexing period, and residence time, are required for each indexer style. The rotary indexing table for the application should also be sized correctly by a reputable manufacturer.

Indexing tables are used in a multitude of industries and in numerous applications. Their design is optimal for many manufacturing jobs, and they are a critical component in most automated manufacturing systems. Indexing tables are best defined as a machine tool positioning device. They carry components in a manufacturing environment with a repeating process of indexing (rotating) around an axis, stopping, dwelling while an operation is performed, then indexing again to repeat the process. They are usually made of circular steel plates, with one or more spindles, a drive system, encoders, sensors, controllers and slots or mounting holes to hold components.

Virtually any manufacturing operation can be performed on a part held by an indexing table including welding, grinding, drilling, assembly, painting, inspection, testing and more. In order to maximize operational efficiency, the machine doing the operation must also be built for the same intended application as the indexing table for them to work in synch. Similarly the machine that loads the indexing table with parts must also be synchronized. They must have the same capacity and be able to manage to the same dwell time for the system to work.

If the timing of these machines are coordinated, the time to operate on or assemble a product can be a fraction of that of workers assembling a product.

Industries that use indexing tables include automotive manufacturers, bottling companies, microchip manufacturers, pharmaceutical makers, consumer products companies and many more. They are invaluable to manufacturers pushing for automation and increased efficiency in their factories, turning work that used to take days into work that takes only hours. If a simple assembly task is required on small parts in a factory, there is no better way to complete the task than by coupling an assembly tool and an indexing table.

Many rotary index table end users need the flexibility afforded by having a fully programmable tool. A seemingly simple way to achieve this is by using a gear head coupled to a servo motor or an AC motor with an encoder. In reality though, while this seems simple and cost-effective, because of the physics described above, high inertia, combined with a goal of high accuracy can create a problematic mis-match.

With a servo-driven barrel cam rotary index table, it’s possible to deliver a wide range of table sizes, with zero backlash and unparalleled accuracy. Servo driven rotary indexers allow heavy inertial loads to be rotated in a very smooth and controlled manner.

Cam-driven rotary index tables can have significant advantages over other types of rotary index table drive systems such as gear drives. Cam-driven rotary index tables provide extremely high accuracy because they operate with no backlash. There are several types of commonly used cam-driven rotary index table systems, each is best for a specific application.

Barrel cams represent strength in indexing. Primarily found in rotary index tables, indexers utilizing barrel cams feature the greatest strength/size offering available.

Globoidal cams are similar to barrel cams in shape (and come from the same steel stock), but have considerably different profiles. Tapered walls in the grooves are designed to accommodate cam followers fixed to an output shaft in a "star" configuration.

Cam driven rotary table indexers are sometimes call "fixed indexers". With a fixed indexer, the cam drives receive constant power input from the motor. This rotates the cam which then rotates the output. Based upon the design of the drive, the output will have "dwell" periods (when the output is stopped) as well as acceleration, deceleration and peak velocity. Cam-driven rotary index tables have a number of advantages, however, they won"t meet the needs of every application.

Rotary index tables can also be "flexible". Flexible rotary index tables use a cam that has a constant lead, that is the output is at a constant velocity if the motor is running at a constant velocity. Constant lead cams provide a high-precision mechanical transition of power to the output and since acceleration and deceleration are still necessary, the logic controller for the index tables motor provides the necessary control.

The rotary table is simply a round flat surface that can be rotated. What makes it interesting is that the table is driven round using a worm and wormwheel arrangement. This means that if a workpiece is mounted on the table it can be machined as it rotates.

On a rotary table the ratio between the worm and wheel is often about 40:1 on a small table but increases with the size of the table. For example a 360mm (12-inch) table might have a ratio of 120:1.

Rotary tables are calibrated round the edge in degrees and have a handle which turns the worm and which, in turn, will rotate the table by 360º divided by the ratio of the worm and wheel. For example, a 360mm (12-inch) table with a 120:1 worm and wheel will rotate by 3º per turn. The handle mechanism has a rotating dial and a Vernier so the angle, on a larger rotary table, can be measured to a few minutes.

Naturally any worm and wheel arrangement on a rotary table is likely to have some backlash. Sometimes this can be compensated for by adjusting the distance between the worm and wheel. Usually any backlash can be ignored if the movement, when machining, is always one way.

The same mechanism can sometimes be used to disengage the worm from the wormwheel. This is useful on large rotary tables because it enables the user to turn the wheel quickly to get from one position to another. (It is not possible to machine the workpiece whilst doing this.)

All rotary tables have a hole in the middle of the table. This is usually a parallel-sided hole but some, especially on smaller rotary tables it is tapered.

This hole can be used to take spigots that can be used to align the rotary table or align the workpiece on the table. Sometimes it is possible to fit a bolt through this hole using various spacers, washers, etc to hold the workpiece on the rotary table.

It is possible the get a device that has a taper on one end that is designed to fit the taper as found on some small rotary tables. The other end has a thread that is designed to fit the backplate as used on the chucks used on some lathes.

All rotary tables can be mounted in the horizontal position on the milling table. Some are designed so they can also be mounted vertically without any other hardware.

Most have slots in the base so they can be bolted to the milling table. Some do not but have a flange so that they can be clamped to the milling table.

It is possible to buy rotary tables that have the facility to tilt the table built in to them. Some even can be tilted at any angle in either or both of two planes at right angles. But all of this adds significantly to the height and weight of the rotary table.

The usefulness of being able to tilt in two planes is very limited and would probably not justify the space it would take up. But a rotary table that tilts in one plane can be useful. This setup can easily be emulated by fitting a rotary table to a tilting table.

Most rotary tables have some means of locking the table at any particular position. Very often an operation is done whilst the table is being rotated in which case the force of the cutter cancels any backlash. However when an operation such as drilling is being done at a particular point then the table should be locked.

Very often a cut needs to be made between two points at the ends of a particular arc. Usually it is not possible to make the cut in one go but several passes are needed. In this case it is useful to have two stops so each cut will start and stop at exactly the same points. This is very useful for preventing mistakes.

The fig. shows a stop. The movable part clamps to the top of the rotary table’s table. Two of these are needed. The fixed part has been fitted to the hole normally used for the locking mechanism as shown in the previous fig.

It will be noticed that the same hole on the rotary table is used for both locking and for a stop. But, of course, in practice, it  will, at any one time, only be needed for one function or the other.

For milling any particular workpiece on a rotary table one has to allow for the space around the workpiece for the clamps used to hold it. For example a 200mm rotary table might hold a workpiece that had to have 120mm hole cut into it. It will be shown later how to effectively extend the diameter of a rotary table. It is often desirable to get the largest rotary table that will fit the milling machine table. However larger rotary tables can be very heavy.

With a large milling machine the practical limit is probably the largest you can lift safely. It is possible to have some sort of lifting gear but this all takes time. It is worth looking carefully before buying because for a given diameter, different makes or different methods of construction can cause a rotary table to vary dramatically in weight.

There will usually be enough space between to milling table and the cutting tool to fit a rotary table to do any required job. But there is always the height of the workpiece to consider. If other devices are to be mounted on the rotary table then the space rapidly disappears.

Most rotary table are set up as shown above to be rotated by a certain number of degrees. This is done using the calibrations on the table marked in degrees.

If it is necessary, when using a rotary table to divide a circle into a number of equal sectors then it is necessary to divide 360º by the number of sectors required. On a small rotary table, the table might only be calibrated to 5°. On larger ones they might be calibrated to individual degrees round the edge but will have a vernier arrangement on the handle so they can be set to a certain number of minutes. This gives us the angle between the sectors. Each time we move from one sector to the next we have to add the angle per sector onto the last angle. For any but the simplest numbers, the chances of getting this right are not great.

It is possible to have dividing plates fitted to a rotating table, as shown above, but this is unusual. But since dividing plates are always fitted to dividing heads these will be covered under dividing heads.

It is quite common to need to be able to divide a circle into so many parts. With dividing plates this is easy and is covered elsewhere. for a rotary table using just degrees and minutes a circle can be divided by one of the following methods.

A     calculate the angle in your head or using a calculator for the origin for each sector and write them down. Most simple calculators will give decimal angles whereas the rotary table is marked in degrees and minutes.

B     use a spreadsheet to produce a list of angles. These will probably be decimal angles. But is then quite easy to turn decimal degrees into degrees and minutes.

C     Use tables showing the angles for each position for a circle divided up to 200 sectors can be found in Appendix C. These are in degrees and minutes.

D     use the table for the first 200 sectors that can be found in “Tables for [the] Cooke Optical Dividing Head” published by Cooke, Troughton and Simms.

Fig. 4—On this tilting rotary table, one servo controls rotation, another controls tilt. Both servocontrols are slaves to the CNC with RS-232 communication, providing five-axis capability from a standard three-axis CNC.

Fig. 1—Modern rotary tables such as this one from SMW Systems have large, widely spaced spindle bearings, large diameter wormwheels and built-in spindle brakes.

If you want to make parts similar to the complex valve body (upper left), an indexer using M-code, RS-232, or “full fourth axis” control is appropriate. Only positioning and rotary cutting moves are required. The center workpiece is a cam that requires simultaneous rotary and linear moves. You’ll need full four-axis control for such workpieces. If you want to do parts similar to the impeller on the right, the contour cutting will require simultaneous five-axis machining.

Many plant managers and shop owners dream of having the latest horizontal machining center (HMC) with all its features, benefits and sophisticated capability. While typical HMC features such as an automatic pallet changer and a 100+ cutting tool magazine are valuable, perhaps the most valuable characteristic is the HMC’s ability to machine on more than one side of the workpiece due to a built-in indexer or full fourth axis.

On complex workpieces that require machining on surfaces not 90 or 180 degrees from each other, indexing or fourth-axis rotation is almost essential to produce the piece. Even when rectangular workpieces with all surfaces 90 or 180 degrees from each other are put on a tombstone, the HMC’s built-in fourth axis of rotation creates a productivity advantage. This is true even if machining on more than one side of the part is not essential.

Any time you can increase the “run cycle,” do more cutting in one operation and avoid handling the workpiece, productivity goes up. Workpiece accuracy also improves. Unclamping and refixturing a workpiece to present a different surface to the cutting tool is always going to introduce some error.

The high cost of horizontal machining centers compared to the incredible values available today in vertical machining centers puts horizontals out of reach for many shops. Fortunately, today there are several suppliers of quality accessories that allow the VMC shop to equip its verticals with indexers, fourth axes and tombstones. These add-ons really work and give many of the benefits of an HMC at a fraction of the price.

Earlier rotary tables and indexers didn’t have the accuracy, rigidity or control flexibility of today’s models. Many shops that tried using indexers in the past had been disappointed in the performance of the older models and abandoned their use in favor of multiple operations, multiple holding fixtures and multiple handlings of the workpiece. They decided that the manual, multiple-operation process was better than trying to use ineffective early model indexers and rotary tables. Today, the situation is different. Manufacturers now offer units that are very accurate, very rigid and have a variety of control and interface options.

The best indexer and control system for you depend on the work you need to do. As with most things, different designs compromise certain capabilities to gain others. Unless you understand these trade-offs, you are at risk of selecting something other than the best system for your requirements. Let’s see what’s available, review the differing capabilities and discuss the advantages and disadvantages of each design. Once you understand the options, you can evaluate them against your requirements and then consider prices and suppliers.

Of course, such a system does not exist. Add the “lowest price from the supplier that gives the best service and support” component and it probably never will exist.

Terminology in the area of indexers is not standard. Terms such as fourth axis, indexer, rotary table and so on are used interchangeably by different machine tool and accessory companies. So, when selecting and buying, you must ask a few questions before assuming you know what you’re going to get. Also, beware of terms such as “precision,” “high precision,” “accurate,” and “rigid.” Is the “brake torque” specification some absolute break away spec or the torque at which some “unacceptable” amount of rotary deflection occurs? Is the “ten arc seconds” accuracy specification certified every one degree, or is it inspected only every 15 degrees? There are no industry standards for specifications and testing. So ask questions and deal with a supplier in which you have confidence, or buy with a guarantee of performance to make your parts.

We’ll start with the mechanical hardware and discuss the electronic control options later. There are at least three common mechanical indexer/rotary table types.

These tables provide infinite positioning as well as the possibility of rotary cutting. A servomotor controlled directly either by the CNC or by a secondary servocontrol rotates a wormscrew, which drives a wormwheel on the rotary table spindle.

The absolute position accuracy of these systems is a function of the quality (precision and accuracy) of the wormgear set (wormscrew and wormwheel), the accuracy and resolution of the servosystem, and the means of servoposition feedback. Most of these servosystems utilize an encoder to monitor the position of the motor rather than the rotary spindle directly. To eliminate any inaccuracies in the wormgears and servo system, some high-end systems use a glass scale or other encoder directly on the rotary spindle to monitor actual rotary spindle position. Figure 1 (at right) shows a typical wormgear rotary table cross section.

If controlled directly by the machine tool’s CNC, they are most commonly referred to as a “full fourth axis.” A full fourth axis has the advantages of having only one CNC program, no programming required by the operator on the shop floor, minimum chance of a crash due to operator error, and the ability to make simultaneous rotary and X, Y or Z moves to do true helical milling operations as required by some more exotic workpieces.

Claims of position accuracy are often misleading since there are no industry standards. Although some manufacturers test and certify absolute position accuracy every one degree, most do not state exactly what their specification means.For all except those few expensive systems with glass scales directly on the rotary spindle, any accuracy specification is for a new table before it has been subjected to any “crashes,” which are not uncommon. Even seemingly small crashes can damage wormgear sets.

Typical infinite positioning wormgear systems utilize a friction brake to hold position against cutting forces. When cutting forces are applied directly on the rotary spindle centerline, friction brakes are generally adequate for most work. However, when cutting forces are applied to workpieces far off centerline, such as on the edge of a part on a tombstone fixture, the resulting torque on the rotary spindle can cause it to deflect. This result is especially likely when heavy cuts produce high thrust forces.

These indexers offer discrete positioning only. Depending on the number of teeth on the face gear, the minimum increment of index might be 15 degrees, 5 degrees or 1 degree. Whatever the minimum increment, only workpieces with angles representing some multiple of the minimum can possibly be machined.

Face gear mechanisms used in indexers are similar to those most commonly found in the turrets of CNC lathes, which by function must index very accurately and very rigidly to withstand the high cutting forces the lathe turret encounters. Face gear mechanisms generally fall into two categories, the two-piece and the three-piece design. Two-piece designs require the face plate of the indexer to “lift” to disengage the face gears. Three-piece designs maintain the same accuracy and rigidity of a two-piece without the need to “lift” the faceplate. In Figure 2 (at right), note the massive face gear that locks the indexer spindle in position.

Assuming it’s a quality face gear set, absolute position accuracy is superb and is maintained for the life of the indexer almost in spite of any “crashes” that might occur. Units with true absolute angular position accuracy of 5 arc seconds or less are available. These units are ideal for the highest precision work such as line boring half way from one side, then indexing 180 degrees and line boring half way from the other side.

Some face gear systems use a servodrive to achieve approximate position and then rely on the face gear for final accurate positioning. These systems are bi-directional and fast. Any random move can be programmed with one simple command. Some other systems use a pneumatic piston to rotate to the approximate position. Typically, these systems rotate only in one direction. All moves must be equal and may require a pause to utilize more then one M-code signal to achieve position. These work but can be tedious to program, set up and operate. They are more prone to crash due to operator error then servodriven units.

These indexers are becoming a thing of the past. They have all the disadvantages of the pneumatic piston driven incremental face gear indexers. Plus, compared to face gear units, they are neither particularly accurate nor rigid. Index positions are usually limited to 15-degree increments. Position is controlled by a pin in a hole or more often by a dog in a notch on the outside of a ring.

Whether you select an infinite positioning wormgear rotary system or a facegear system as the best mechanical design for your work, your next decision involves how you will control the rotary axis.

With a pneumatic incremental indexer, you probably will have no choice. Your machine’s CNC will control the indexer by communicating with a special indexer control via an M-code.

If you select a system with a servodrive, you have three choices: 1.) direct “full fourth axis” using only the machine’s CNC, 2.) an M-code command from the CNC to a separate rotary control, or 3.) RS-232 communication between the machine’s CNC and a separate rotary control. Each of these choices has advantages and disadvantages.

A single, four-axis CNC is the easiest to use and provides the most control. Four-axis CNC is best for certain kinds of workpieces. Full four-axis control systems are usually ordered for delivery with a new machine. Systems can be retrofitted; however, retrofitting is complicated and expensive. The advantages of a single four-axis control are numerous, and the disadvantages are primarily related to cost.

The single CNC constantly tracks all three linear axes (X,Y,Z) and the rotary axis. This provides the ability to do precise helical cutting with simultaneous rotary and X, Y or Z moves.

While a few machine builders offer a full four-axis control with rotary table for about 10 percent of the base price of the machine, most charge more than 20 percent.

Very few machine builders make it easy to retrofit a full four-axis rotary table. For most builders, retrofitting is a complicated process, and the cost typically exceeds 30 percent of a base machine price.

The motor for the rotary axis must be matched to the servodrive of the CNC. Because cable connections are not standard from one machine builder to another, rotary tables can not generally be used on more than one machine.

Some applications may require the accuracy and rigidity of a face gear system. However, many machine builders don’t offer face gear systems with a full four-axis control, although such systems are feasible.

An M-code actuated system provides a fourth axis of motion by combining a standard three-axis CNC with a rotary table or face gear indexer that has its own separate rotary servocontrol. The rotary program is entered and stored in the separate rotary servocontrol. The CNC communicates with the rotary control via an M-code. When the rotary control receives the M-code signal, it executes the next rotary move stored in its memory, then sends a signal back to the CNC, telling it that the move has been completed.

Typically, the rotary program includes many separate rotary moves. One move might be a simple index to position at full rapid speed. Another might be a slower rotary move to machine a groove or other feature on the workpiece. Figure 3 (at right) shows a typical rotary servocontrol system.

High quality M-code controlled systems are available from several suppliers for a price of about 10 percent of a base machine price. (For example, a 5C rotary system at $6,000; a 6-inch faceplate system at $7,000; a 9-inch system at $10,000; and so on).

Requiring only one M-code, 110V power and an air line for operation, these systems can be retrofitted to almost any CNC machine, typically with less than a day of downtime.

Systems can be moved from one machine to another as long as the next machine can issue M-codes. A shop with multiple machines and multiple rotary systems can select the best system for each job regardless of the machine. For example, a small indexer can be used for small parts to avoid cutting tool interference problems and to minimize indexing times. A big indexer can be used for big parts. A face gear indexer can be used when the maximum in accuracy and rigidity are needed and the work can be accommodated by multiples of 5 degrees of index.

The machine operator needs to enter the rotary program into the rotary servocontrol, or select the right program if it’s already stored in the rotary control’s memory. This takes some time, and there is the chance of an error.

If the machining cycle is ever interrupted in mid-cycle, such as to inspect a workpiece feature or replace a worn cutting tool, the operator must be sure to back up the rotary program and the CNC program to a point that keeps the two programs in sync. This step can be confusing, and any error can result in a “crash,” with a cutting tool coming down to a workpiece rotated to the wrong position.

Although it is possible to perform simultaneous rotary and X, Y or Z moves, they are not recommended. If you have patience and can afford to scrap a few parts, you can use trial and error to find the right rotary speed to match the linear move and determine starting points that match.

Recently developed, RS-232 communication between a three-axis CNC and a rotary servocontrol offers advantages of full four-axis and M-code operation. RS-232 is the commonly used, standard electrical interface for connecting peripheral devices to a computer. Personal computers often use the RS-232 communication protocol to send information to a printer. Another common use for RS-232 communications is connecting a PC to an external modem.

Nearly all CNC units have an RS-232 port, and it is commonly used to exchange CNC programs between a computer system and the CNC. More recently, RS-232 connections have been used by CNCs to communicate with robots and rotary tables. To communicate with the rotary table’s control, a special line of code is inserted into the CNC program. This line of code sends a string of numbers and letters through the RS-232 port to the rotary table control, which translates the string of code into rotary moves.

RS-232 communication between a three-axis CNC and a rotary servocontrol provides much of the best of both worlds of full four-axis and M-code operation. Both the linear and rotary moves are stored in the CNC as part of the workpiece program. When a rotary move is required, the CNC sends the commands for that one move (rotary speed and angle of rotation) through an RS-232 line to the rotary control.

The rotary control executes that one move and sends back a signal to the CNC, indicating that this move has been completed. The CNC then commands its next linear move. The separate rotary servocontrol simply works as a slave to the CNC. The machine operator turns the rotary control on in the morning and does not need to attend to it the rest of the day. Figure 4 (at right) shows a tilting rotary table system utilizing two rotary servocontrols with RS-232, providing five-axis capability from a standard three-axis CNC.

Crashes are nearly as unlikely as with a full four-axis control. The correct rotary program is always selected because it is part of the total workpiece program stored in the machine’s CNC. Note: Rotary moves should be programmed in “absolute position” so that if the machining cycle is interrupted, the operator can back up the CNC program to just in front of a rotary move, then safely resume the program.

Retrofitting is easy provided the machine’s CNC has an RS-232 port and appropriate communication software, which may already reside in the CNC or be available from the machine builder.

With RS-232, two rotary controls can be operated by most three-axis CNCs with only one RS-232 port. Five-axis capability with a tilting rotary table setup can be retrofitted to a three-axis machine for about $25,000 (a new, full five-axis VMC option is typically priced at $95,000).

Both the work you need to do and the machines you own or intend to purchase will influence what you select for a rotary axis. These guidelines summarize what you should consider.

When buying a new machine, get prices on everything the builder offers, no matter what kind of workpieces you’ll be machining. If the builder offers a full four-axis system with a high-quality, infinite-positioning rotary table at a price of about 10 percent off the base machine, this system will probably be your best choice.

If your workpieces can take advantage of the accuracy and rigidity of a face-gear system, and you can live with the 5-degree minimum increment, a face gear system controlled by RS-232 or M-code is a good choice. A few builders offer a face gear system with true four-axis control.

If you’re doing a variety of work that requires simultaneous rotary and linear helical moves, you’ll probably want a true four-axis system regardless of the cost. However, you should consider a more economically priced RS-232 or M-code system when you are retrofitting an existing machine and have only a couple of jobs requiring these moves, especially if these jobs are long run and you can afford some extra programming and setup time. These systems are worth considering if you simply can’t afford the price of a true fourth axis.

If you’re retrofitting existing machines, especially if you have several and want to do rotary work on more then one of them, check with the builder on the cost of upgrading to full four axis. You may conclude that the cost and flexibility advantages of RS-232 or M-code will make one of them the best choice.

Adding a rotary axis to a VMC is worthwhile whether you want to do full four-axis simultaneous machining of exotic workpieces, simple indexing of parts that need machining on surfaces not at 90 degrees from each other, or tombstone processing of rectangular parts that benefit from a longer unmanned machining cycle. Today, many good options exist. If you’re buying a new machine, have the builder quote the optional systems it offers. If you’re going to retrofit an existing machine, contact either the original supplier or the companies that offer complete indexer and rotary table systems. Retrofitting is highly affordable. (Systems from SMW Systems, for example, generally cost a little over $1,000 per inch of faceplate diameter, including installation and training.) MMS

Mitee-Bite Products’ fixtures demonstrated their powerful clamping support in a project with Akron Gear & Engineering to vertically hold a 1-ton ring during machining.

Mr. Straessle is pL Lehmann product manager at Exsys Tool. He says that while five-axis machines have become more affordable, they still can be two to three times the cost of a three-axis VMC, depending on the model. Therein lies one advantage to rotary tables, which, when installed on the bed of a three-axis VMC, combine a rotational C axis and a tilting A axis to enable the machine to perform either five-axis positioning work (aka 3+2 machining) or full five-axis contouring. Three-axis VMCs outfitted with two-axis rotary tables are commonly smaller than five-axis machines, too, saving valuable floor space. Unfortunately, they also tend to have tighter work envelopes, meaning a sizeable rotary table will be more restrictive of a machine’s movements.

A compact rotary table preserves work envelope space, providing more room for spindle and tool movement. Plus, shops have the option to use just the rotary table, mount standard vises next to it or remove the rotary table altogether, which is made simpler when the rotary table has a zero-point-type locating system to eliminate the need for alignment when it is removed and then remounted.

That said, Mr. Straessle says compact rotary tables still must possess design elements that enable them to perform effectively for a range of work. Here, he details four such features inherent to the pL Lehmann 500 series of modular-designed rotary tables, available in North America through Exsys Tool.

1. Load capacity. The compact 500 series provides load capacities that, in the past, were only available with larger rotary tables. For instance, the 3-inch rotary tables in this series are generally half the size of comparable units, but can handle workpiece loads as heavy as 400 pounds, he says.

2. Speed and torque.Rotary tables commonly use either direct-drive or gear-driven technologies, the former able to achieve high rotational speeds and the latter offering high torque. The 500 series uses the company’s pre-loaded gear drive (PGD) design, which is said to offer the best of both worlds in terms of high speed and high torque while being as much as four times as rigid as direct-drive systems. Plus, it enables the rotary tables to generate rotational speeds as fast as 160 rpm with virtually zero backlash.

3. Spindle clamping power.Once a rotary table is oriented to the desired position, an effective spindle clamping system is needed to securely hold that position during machining operations. Some rotary tables use an external intensifier or some other type of standalone hydraulic unit combined with disc braking to achieve necessary clamping forces. Conversely, the 500 series features an integral unit that converts air pressure into hydraulic holding power, using a

cylinder/piston mechanism that requires only 90 psi of air pressure to generate more than 3,000 psi of hydraulic clamping pressure to firmly clamp the spindle in place at any position around its 360 degrees of rotation. In addition, this air-over-oil clamping system can often achieve unclamp-to-clamp times of less than 0.4 second as compared to the multiple seconds external systems typically require.

4. Monitoring system.The 500 series features a self-contained, internal monitoring system used to track and record vital rotary table information, including temperature, rotational speed and clamping force. It also detects internal pressure decay.

In addition, the rotary tables have USB ports to enable users to download monitoring data to log the operational history of the table. Not only does this data highlight crashes or malfunctions, but it also facilitates more effective preventive maintenance by offering early warnings to possible issues so users can avoid unplanned downtime. Plus, the monitoring system activates a series of LED warning lights when it recognizes a potential problem. For example, a blinking orange light is an alert to a situation that can be addressed before it becomes serious, while a continuous red light means immediate attention is needed. Because these rotary tables integrate with all the common machine tool CNCs, users can have warnings displayed on the control screens, too. By connecting a laptop running software such as pL Lehmann’s TeamViewer, users can also solicit assistance via the Internet from a company technician who can log on to assist in troubleshooting.

Mr. Straessle says the company guarantees the spindles on its standard rotary tables to achieve runout of 5 microns and its high-accuracy models to achieve runout of less than 3 microns (the latter is commonly used in grinding applications). In addition, glass scales provide ±1-arcsecond positioning capability for the C axis. These rotary tables are also sealed to prevent internal contamination that could hinder performance and feature a motor housing internally pressurized with oil to achieve an IP67 rating.

The 500 series is available in four standard, single-fourth-axis models. The smallest is the EA 507, offering a 3-inch face diameter and a spindle nose load capacity of approximately 240 pounds, while the high-speed EA 511 model is said to deliver twice the speed of the standard models. Each model can be configured as a two-axis system that provides 180 degrees of A-axis tilt with full C-axis rotation, as is the case with the series 500 T1 (trunnion-style) and TF (cantilever-style) units. They can also be ganged together with multiple spindles/C axes.

Many job shops start in a garage with a used mill and a manual lathe. The owners of this Utah job shop took a different tack. Along the way to a very successful business, they"ve debunked a bunch of myths commonly held about job shops.

Modular fixturing makes sense for this manufacturer, whether it"s machining one- or two-of-a-kind parts for its custom machine tools or larger quantities for its contract machining business.

At Rusach International,rotary table design, engineering and manufacturing & pallet system design, engineering and manufacturing is our specialty. We can supply rotary tables from 100mm up to 8 Meters in diameter.  See our rotary table pages.  We specialize in high accuracy, up to +/- 1 arc second, heavy load capacity, large work pieces, production style, heavy duty rotary tables and pallet shuttle/storage/transfer systems.  We also have a line of standard small production tables that are very cost effective, yet can be customized per application.

Rusach International systems are not proprietary and therefore can be integrated into any machine, control system or application. We do not believe in “locking” a customer down with proprietary parts!  We work with all the major industry control, motor and encoder manufacturers.

Manufacturer of standard and custom 360 degree linear rotary tables for scanning, assembly, testing and production applications. Features vary depending upon model, including worm and gear drive design with central rotating ball bearings, manual and motorized operation, hollow spindles, four mounting holes, accessible adjustment clamps and graduated knobs. Accessories such as rotating table adapter plates, brackets, platform shelves, thumbscrew locks, alternative knobs, limit switches provided. Manually operated rotary motion turntables also available. Suitable for mounting and rotation of test specimens, cameras, transducers, sensors, mirrors and other components. Stock items and repair services are offered. One year warranty. Made in the USA.

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