Turntable bearings

The commonly used rotary workbench in CNC machine tools includes indexing workbench and CNC rotary workbench.

The CNC rotary table can be used to achieve a circular feed movement. In addition to realizing the circular feed movement, the CNC rotary table (referred to as the CNC turntable) can also complete the indexing movement.

The rotary table is widely used in various CNC milling machines, boring machines, various vertical lathes, end milling and other machine tools. In addition to the requirement that the rotary table can bear the weight of the workpiece well, it is also necessary to ensure its rotation accuracy under load.

The turntable bearing, as the core component of the turntable, not only needs to have a high load capacity, but also has high rotation accuracy, high anti-overturning ability, and high speed capacity during the operation of the turntable.

In the design of rotary tables, the most used bearing types are roughly divided into the following types:

Thrust ball bearings: cylindrical roller bearings

Thrust ball bearings can withstand a certain axial force, so the bearing is mainly used to bear the weight of the workpiece; Cylindrical roller bearings, on the other hand, are mainly used for radial positioning and to withstand external radial forces (such as cutting forces, milling forces, etc.). This type of design is widely used and relatively inexpensive. Because the thrust ball is a point-contact bearing, its axial bearing capacity is relatively limited, and it is mainly used in small or medium-sized machine tool rotary tables. In addition, lubrication of thrust balls is also more difficult.

Hydrostatic bearings: Precision cylindrical roller bearings

Hydrostatic bearing is a kind of sliding bearing that relies on the external supply of pressure oil and establishes a hydrostatic load-bearing oil film in the bearing to achieve liquid lubrication. The hydrostatic bearing always works under liquid lubrication from start to stop, so there is no wear, long service life and low starting power; In addition, this kind of bearing also has the advantages of high rotation accuracy, large oil film stiffness, and can suppress oil film oscillation. Precision cylindrical roller bearings have a good radial bearing capacity, and due to the use of precision bearings, the rotation accuracy of the rotary table can also be well guaranteed. The rotary tables using this design can withstand very high axial forces, some of which weigh more than 200 tons and have a turntable diameter of more than 10 meters. However, this type of design also has some shortcomings, because the hydrostatic bearing must be equipped with a special oil supply system to supply pressure oil, the maintenance is more complicated, and the cost is relatively high.

Crossed roller bearings

The application of crossed roller bearings on turntables is also relatively common. Crossed roller bearings are characterized by two raceways in the bearing, two rows of cross-arranged rollers. Compared to traditional thrust bearing radial centering bearing combinations, crossed roller bearings are compact, compact and simplify table design, thereby reducing the cost of the turntable.

In addition, due to the optimised preload, the bearings have a high degree of stiffness, which ensures the stiffness and precision of the turntable. Thanks to the design of the two rows of crossed rollers, the effective span of the bearing can be significantly increased, so that these bearings have a high resistance to overturning moments. In crossed roller bearings, there are two types: the first is cylindrical crossed roller bearings, and the second is tapered crossed roller bearings. In general, cylindrical crossed roller bearings are less expensive than tapered crossed roller bearings and are suitable for turntable applications with relatively low speeds; The tapered crossed roller bearing adopts the pure rolling design of the tapered roller, so this type of bearing has:

• High running accuracy

• High speed capability

• Reduced shaft length and machining costs, limited variation in geometry due to thermal expansion

• Nylon divider, low moment of inertia, low starting torque, easy to control angular indexing

• Optimized preload, high stiffness and low runout

•Linear contact, high stiffness, high precision of guiding roller operation

• Carburized steel provides excellent impact resistance and surface wear resistance

• Simple but well-lubricated

When mounting the bearings, the customer only needs to preload the crossed roller bearings to the recommended values, rather than having to have a complex mounting adjustment process like hydrostatic bearings. Crossed roller bearings are easy to install and easy to adjust the original installation form or maintenance method. Crossed roller bearings are suitable for all types of vertical or horizontal boring machines, as well as applications such as vertical mills, vertical turning and large gear milling machines.

As the core component of the spindle and turntable of the machine tool, the bearing plays a pivotal role in the operation performance of the machine tool. In order to be able to select the right size and type of bearing, we need to consider various operating conditions, such as running speed, lubrication, mounting type, spindle stiffness, accuracy and other requirements. As far as the bearing itself is concerned, it is only by fully understanding its design features and the resulting advantages and disadvantages that we can bring out the best performance of the bearing.
If you want to know more bearing information,please contact us :
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