Screws for CNC: purpose, characteristics, types

Ball screw for CNC is a ball bearing unit that eliminates friction and is able to withstand the main load when pressing the workpiece. To select the required design, there are classes of accuracy 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 for structural dimensions. To select a bearing pair, you should take into account the strength parameters of the material, the efficiency, the smooth running, 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, for large and small loads, with a cylindrical nut. The choice of bearing arrangement is also influenced by the position 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 better to choose?

The CNC machines of the CNC machines of the budget variant are chosen of rolled type. They are not inferior in accuracy more costly, but the stock of service life for such species is low. If greater accuracy is required, then the bearing pairs are ground.

With a heavy load on the axle, it is recommended that you choose a special type that allows you to withstand even mechanical shocks against the tool. They put a threefold margin of safety compared to 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.

On sale, you can also find parts for the ball screws of early releases. To simplify the repair procedure, there are already assembled designs: 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 is always given a guarantee and recommendations for maintenance.

Accounting for other components

To select the ball screw, you need to collect the necessary information. 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 the constant modernization of equipment. 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 fastenings for rulers instead of obsolete encoders, which complicates installation and adjustment 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, the crushing of the ball screw on the part is used. 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 separate spare part, which is rare, then you can extract 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 reduced rigidity. 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 manufacturers also 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, often experiments cost more than the cost of paying for a quality product 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.

Mistrust among consumers is caused by new manufacturing companies that have no 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 limited to the minimum number. 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 than to lubricate 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 be affected by insufficient hardness of the surface, on this parameter often save manufacturers with the label no name.

Often, instead of this steel is taken cheaper and less resistant to loads. Gaskets and liners made of plastic must be oil-resistant, they often crumble in the cheap versions of ball screws. Balls in bearings are erased faster because of the discrepancy between the speed regimes actually indicated in the passport.

Node device

The ball screw is required to convert the rotational motion to the translational motion 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 the 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 the manual assembly of the assembly. Improper tightening reduces the service life of the elements.

Standard products have from one to six 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 overestimated grinding parameters.

Pros of the transition to ball bearings

Before other types of knots for moving axes in CNC machines, ball screws 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 assemblies are light in weight and small in 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.