Ball screw for CNC is a ball-bearing pair assembly that eliminates friction and is able to withstand the main load when a part is pressed. To select the desired design, there are accuracy classes, on which the final cost of the machine depends. By means of ballscrews (ball screw transmission) linear displacement is converted into rotational one.
Definitions
Ballscrew for CNC refers to costly components. It is not recommended to save here, the safety margin is required in three times. The inexperience of the operator will result in a long and costly repair. The market offers a huge number of products, to understand which is not easy for a beginner.
Not every ballscrew for CNC is suitable only in structural dimensions. To select a bearing pair, one should take into account the parameters of material strength, efficiency, smoothness, maximum load, level of heat loss during intensive work. To fulfill the specified requirements, the type and purpose of ballscrews are selected.
Ball screws for CNC are rolled, polished, for large and small loads, with a cylindrical nut. The choice is also affected by the location of the bearing pair: horizontal or vertical. In the latter case, the bearing load is taken into account. To reduce this force in the machines, an inclined support arrangement is provided, but in some models the verticality is laid down by the requirements of technological operations.
Which is better to choose?
Ballscrews of CNC machines of a budget option are selected of rolled type. They are not inferior in accuracy to more expensive ones, but the margin of service life of such species is low. If greater accuracy is required, then polished bearing pairs are bought.
With a heavy axle load, it is recommended to choose a special type that can withstand even mechanical impacts on the tool. They have a three-fold safety margin in comparison with conventional ball screws for CNC. In St. Petersburg there are similar offers for each type of machine. However, not all models are available; delivery time will be required.
On sale, you can also find accessories for ballscrew assemblies of earlier releases. 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 , product dealers have specialists who can calculate the basic parameters of the product. The sold unit is always given a guarantee and service recommendations.
Accounting for other components
To select the ballscrew, the necessary information should be collected. Important characteristics are the type of control system, motor, the used coupling or gearbox, the number of circular sensors and the method of mounting on the axis. The ideal solution would be to buy spare parts from one manufacturer, but this result is not always obtained.
This is due to the continuous modernization of equipment. The three-year-old machine can already be discontinued, and its components do not meet the requirements of new technological procedures. Each year, the calculated axle load increases due to an increase in the speed of the tool.
Newer models of the machine may contain fasteners for rulers instead of obsolete encoders, which complicates on-site installation and commissioning. Also, the holes for the limit switches or inductive sensors of the final position are distinguished. Another type of product may not take into account which ball screw lubrication is used on the CNC machine.
Allowed Savings
To save the budget, ball screws are crushed into parts. CNC machines are always fully collapsible to replace the smallest parts. However, before dismantling, you should familiarize yourself with the offers on the market.
If it is possible to supply a separate spare part, which is not common, then you can remove the part. However, it can be cheaper to buy ballscrews in full to ensure factory-made precision fitting of components and maintain a product warranty.
It happens that ball screws already have a margin of safety, which is often not used. Therefore, it is allowed to install bearing pairs of low stiffness. But if the seller considers the working conditions of the unit unsatisfactory, then he may not give a guarantee or reduce its validity.
Is it worth taking branded products?
Practice has shown that famous manufacturers also have a percentage of defective products. But he, of course, is much lower. However, if you understand the distinguishing features of low-quality goods, then you can buy ball screws. Verified companies can provide goods no worse than branded ones in terms of accuracy and rigidity.
However, often experiments are more expensive than the cost of paying for a quality product with a difficult technical restoration of the production process after repair. You can buy analogues of Korean or Chinese companies on a small machine, but a robust part is required for a massive multi-axis control center. You can find out about the quality of any product by customer reviews.
Distrust among consumers is caused by new manufacturing companies that do not have experience in the manufacture of such products. To assess such market participants resort to comparing the characteristics of the product. Initially, the cost of any ballscrew is the minimum figure. If the product is cheaper, then it physically cannot meet the stated indicators. Therefore, the pursuit of savings should be reasonable.
Parameters affecting the wear of the assembly
When choosing a new spare part, it is important to inquire how to lubricate a CNC ball screw. The use of another type or cheaper liquid will reduce the durability of the unit, which will affect warranty repair and completely disable the bearings. Wear will be affected by insufficient surface hardness, manufacturers with the no name label often save on this parameter.
Often, instead of the specified steel, a cheaper and less resistant to loads is taken. Gaskets and liners made of plastic should be oil resistant, they often scatter with cheap ball screw options. Balls in bearings wear out faster due to the mismatch of the speed modes actually indicated in the passport.
Node device
Ball screw is required to convert rotational motion into translational and vice versa. Therefore, the base of the assembly included balls rubbing between themselves and the surface of the bearing walls. The number of internal elements determines the accuracy of movements.
Balls are clamped between the screw and nut with a certain moment, which many locksmiths do not take into account when manually assembling the assembly. Incorrect tightening reduces the service life of the elements.
Standard products have from one to six grooves serving as raceways for balls placed between the turns of the nut and screw. The more of them, the longer the ball screws can withstand under high load. These nodes have overestimated grinding performance.
Pros of moving to ball bearings
In front of other types of nodes for moving axles in machines with CNC ball screws, products have more attractive characteristics. The transmission efficiency is more than 80% due to reduced slip due to special grooves. Hence low friction and heat loss.
When using alloy steels, the units are light weight and small in size. Also, increased accuracy of movements and the smooth running of the assembly compatible with this are realized. However, due to the complexity of manufacturing ballscrews, they are much more expensive than linear systems.