Screws for CNC: purpose, characteristics, types

The ball screw for CNC is a ball bearing unit,A friction-free and capable of withstanding the main load when pressed on a part. To select the required design, there are accuracy classes on which the final cost of the machine also depends. By means of a ball screw (ball screw), the linear displacement is converted into a rotary motion.

Definitions

The screw for CNC refers to costly nodes. It is not recommended to save here, the margin of safety is needed at three times the size. Inexperience of the operator will result in a long and expensive repair. The market offers a huge number of products, which it is not easy for a beginner to understand.

Not every ball screw for CNC is suitable only forconstructive dimensions. To select a bearing pair, you should take into account the strength parameters of the material, the efficiency, the smoothness of the stroke, the maximum load, the level of heat loss during intensive work. To meet the specified requirements, the type and purpose of the ball screw is selected.

Ball screws for CNC are rolled, ground, forlarge and small loads, with a cylindrical nut. The choice of bearing arrangement is also influenced by the location of the bearing pair: horizontal or vertical. In the latter case, the load on the support bearing is taken into account. To reduce this force in the machines provides an oblique location of the support, but in some models, verticality is laid down by the requirements of technological operations.

Which are the best to choose?

The CNC machines of the CNC budget variant are selectedrolled type. They are not inferior in exactly the more costly, but the service life of such species is low. If more precision is required, then the bearing pairs are ground.

With a heavy load on the axle, it is recommendedchoose a special kind that allows you to withstand even mechanical shocks about the instrument. They put a three-fold safety margin in comparison with conventional ball screws for CNC. In St. Petersburg there are similar proposals for each type of machine. However, not all models are available, it will take time for delivery.

In addition, you can find accessories for ball screwsnodes of early issues. To simplify the repair procedure, there are already assembled structures: calipers of serial models of machine tools. To facilitate the selection of the bearing assembly, the product dealers have specialists able to calculate the basic parameters of the product. The sold unit always has warranty and service recommendations.

Accounting for other components

To select a ball screw, you must collect the necessaryinformation. Important characteristics are the type of control system, the motor, the coupling or reducer used, the number of circular sensors and the method of mounting on the axis. The ideal solution is to buy parts of one manufacturer, but this result is not always obtained.

This is due to constant modernizationequipment. The three-year-old machine can already be removed from production, and its components do not meet the requirements of new technological procedures. Every year the design load on the axle increases due to the increased speed of the tool.

New models of the machine can contain fasteners forRulers instead of obsolete encoders, which complicates installation and commissioning on site. Also, there are different end-hole openings or inductive end position sensors. Another type of product may not take into account which lubricant is used on the CNC machine.

Allowable savings

To save the budget, crushing the ball screwson the part. CNC machines are always completely collapsible to replace the smallest parts. However, before dismantling works, you should familiarize yourself with the offers on the market.

If it is possible to supply a separatespare parts, which is infrequent, it is possible to remove the part. However, it is cheaper to buy the ball screws completely, in order to ensure the factory accuracy of fitting the components and maintain the product warranty.

It happens that the ball screw already has a safety margin,which is often never used. Therefore, it is allowed to install bearing pairs of low stiffness. But if the seller considers the working conditions of the node unsatisfactory, then he may not give a guarantee or reduce the duration of its operation.

Should I take branded products?

Practice has shown that famous manufacturersalso have a percentage of defective products. But, of course, it is much lower. However, if you understand the distinguishing features of a poor-quality product, you can buy ball screws. Proven firms can provide goods not worse than branded ones and in terms of accuracy and rigidity.

However, experiments often cost more than costsfor the payment of quality goods with a complex technical restoration of the production process after repair. On the small machine you can buy analogues of Korean or Chinese companies, but for a massive multi-axis control center, the detail is reliable. You can find out about the quality of any product from the feedback of customers.

Distrust of consumers causes newManufacturers who do not have experience in manufacturing such products. To assess such market participants resort to comparing the characteristics of the goods. Initially, the cost of any ball screw is fixed with a minimum figure. If the product is cheaper, then it physically can not meet the declared rates. Therefore, the pursuit of savings should be reasonable.

Influencing the wear of the node parameters

When choosing a new spare part it is important to inquire thanlubricate the CNC ball screw. The use of another type or cheaper fluid will reduce the longevity of the unit, which will affect the warranty repair and completely disable the bearings. The wear will affect the insufficient hardness of the surface, this parameter is often saved by manufacturers with the label no name.

Often instead of this steel is taken morecheap and less resistant to stress. Gaskets and liners made of plastic must be oil-resistant, they often crumble off cheap ball screws. Balls in bearings are erased faster due to inconsistencies in the speed regimes actually indicated in the passport.

Node device

The ball screw is required to convert the rotarymotion into the translational and vice versa. Therefore, the basis of the assembly included balls, rubbing between themselves and the surface of the walls of the bearing. The number of internal elements determines the accuracy of movements.

The balls are clamped between the screw and the nut with a certain torque, which is not taken into account by many locksmiths during manual assembly of the assembly. Improper tightening reduces the service life of the elements.

Standard products have from one to sixThe grooves serving as raceways for balls placed between turns of a nut and the screw. The more of them, the longer it will withstand the ball screws under high load. These nodes have excessive grinding parameters.

Pros of the transition to ball bearings

Before other types of nodes to move the axes inCNC machine tools have more attractive characteristics. Transmission efficiency is more than 80% due to slip reduction due to special grooves. Hence, small friction and heat losses.

When using alloy steels, the nodes havelight weight and small size. Also, increased accuracy of movements and compatible smooth running of the unit are realized. However, due to the complexity of manufacturing the ball screws, the order is more expensive than linear systems.