Today, let's talk about rack and pinion VS ball screw. In the mechanical field, this has always been a controversial topic-should I use a rack and pinion or a ball screw? As we all know, the role of the two is to convert the rotary motion into a linear motion system to move and position the machine, so they have been applied in many industries.
What is the real difference between them? Why did the company choose one to use the other? Or, why use both at the same time?
Most people are biased against actual differences. Some people even exaggerated or misunderstood the information to discourage potential buyers from competing with competitors.
Basically, FORSUN CNC's CNC machines use ball screws and racks, and pinions at the same time. Usually, each CNC router machine adopts a spiral rack and pinion transmission on our X and Y axis and uses a ball screw on the Z-axis to control the milling head.
Let us analyze the application of rack & pinion and ball screw in the CNC router machine industry.
What is a rack-and-pinion transmission system?
The rack-and-pinion transmission system refers to a rack bolted to the side of the machine and pinion gear or gear/gear that meshes with the rack. As the pinion rotates, the machine moves. In the CNC router machine industry, spiral (angled) frames are widely used to incorporate drives.
Advantages of rack and pinion transmission system
The rack and pinion drive is known for its rigidity and can provide precise motion for an unlimited length of time. They are constructed to travel the entire distance of the machine regardless of length, without worrying about "spiral whiplash" (more on this later). The rack and pinion system has a long normal operation time, can be produced for several years, with minimal wear, and is very beneficial in the environment of the factory floor, almost free from dust and debris.
The design of the helical rack and pinion is angled, not straight, and there are more teeth in the mesh of the rack. The spiral design enables smooth, low-friction movement and provides zero backlashes with a position accuracy of ±.001 inches throughout the machine stroke. They also have excellent acceleration, deceleration, and processing capabilities to maintain higher speeds, which are the result of their constant stiffness and excellent power or efficiency transfer (up to 97% or more).
The simplicity of the rack and pinion design is a huge advantage that benefits the end-user. They are usually simple bolted connection systems that are easy to replace-no special skills or knowledge are required.
Disadvantages of rack and pinion transmission system
The processing accuracy and processing technology requirements are high. If processing technology and processing technology cannot be achieved, there will be high friction and potential gaps between the rack and pinion. Fortunately, with the advancement of production technology, such as the improvement of milling, grinding and heat treatment processes, the transmission accuracy and load-carrying capacity of racks and pinions have been greatly improved.
What is a ball screw transmission system?
Ball screw is an ideal product that converts rotary motion into linear motion or converts linear motion into rotary motion. The ball screw is composed of a screw, a nut, and a ball. Its function is to convert rotary motion into linear motion, which is a further extension and development of the trapezoidal screw. The important significance of this development is to change the sliding of the screw into rolling and reduce friction. Because of its small frictional resistance, ball screws are widely used in various industrial equipment and precision instruments.
Advantages of ball screw
After the operation is completed correctly, the ball screw will have excellent accuracy, will not produce friction, and can slide smoothly. There are more installation options. The frame must be bolted along the entire length, and ball screws may be more suitable for certain machine designs. The ball screw system is also easier to use in the manufacturing process, in which case the rack and pinion may require more processes to build correctly.
Disadvantages of ball screw
As mentioned above, ball screws are known for being precise and frictionless. However, on longer shafts, the vibration may get worse as the speed needs to be increased, thus making the screw spin faster. This problem is called "screw whip". A ball screw-driven system may require a larger motor or more gear compensation to compensate for the "screw" and maintain the positioning speed of the machine, so it is not ideal to use a ball screw on a shaft longer than 4′. Due to the short-stroke distance, the ball screw system is most suitable for height positioning or Z-axis.
In terms of speed, the ball screw cannot accelerate at the fastest speed, nor can it maintain a higher speed with higher efficiency. Their stiffness is lower and less constant. Their power or efficiency transfer is in the range of 80-85%.
The maintainability of the ball screw system is also tricky, and usually requires specialized skills to replace it, because the ball screw can be very sensitive, so this is not an ideal choice. Ball nuts are very sensitive to misalignment, especially when opposing nuts are used. Ball screws are also more susceptible to contamination, and will not tolerate harsh environments that can lead to catastrophic failures (such as stone shops).