A ball screw in a CNC machine is a precision transmission component that converts motor rotation into accurate linear motion. It is commonly used on CNC routers, milling machines, lathes, engraving machines, plasma machines, and other CNC motion systems.
For CNC equipment, the ball screw directly affects positioning accuracy, repeatability, feed smoothness, cutting stability, and long-term machine performance.
In one CNC milling machine case, the X and Y axes showed inconsistent positioning, with errors reaching about 0.08 mm. After replacing the worn lead screws with C5-grade ground ball screw sets and re-aligning the linear motion system, the repeatability improved to around 0.01 mm. This shows why the ball screw is one of the key components in CNC machine accuracy.
What Is a Ball Screw in CNC Machine?
A ball screw in a CNC machine is a mechanical device that uses a screw shaft, ball nut, and recirculating balls to convert rotary motion into linear motion. When the motor rotates the screw shaft, the ball nut moves along the shaft and drives the CNC axis forward or backward.
In simple terms, the motor provides rotation, the screw converts that rotation into straight-line movement, and the CNC axis moves according to the programmed tool path.
Basic motion process:
1. The servo motor or stepper motor rotates the ball screw shaft.
2. The steel balls roll between the screw shaft and the ball nut.
3. The ball nut moves linearly along the screw shaft.
4. The CNC table, gantry, or spindle axis moves with the nut.
Because the movement is based on rolling contact instead of sliding contact, ball screws can provide high efficiency, low friction, smooth movement, and good positioning accuracy.
Why CNC Machines Use Ball Screws Instead of Lead Screws
Lead screws move through sliding friction between the screw and nut. This structure can work for simple, low-speed, or low-cost machines, but sliding friction can create more wear, heat, and backlash over time.
A CNC machine needs stable feed motion, low backlash, repeatable positioning, and reliable movement under cutting conditions. Ball screws are better suited for these requirements because the rolling balls reduce friction and improve transmission efficiency.
In many CNC applications, ball screw efficiency can reach about 90–95%, which helps the motor drive the axis with less power loss compared with traditional sliding screw systems.
| Comparison Item | Ball Screw in CNC Machine | Lead Screw |
|---|---|---|
| Contact Form | Rolling contact through steel balls | Sliding contact between screw and nut |
| Efficiency | Usually high, often around 90–95% | Lower because of sliding friction |
| Backlash Control | Can be reduced with preload | Usually more difficult to control over long-term wear |
| Wear | Lower friction helps reduce wear | Sliding friction may increase wear over time |
| CNC Suitability | Suitable for accurate and repeatable CNC feed motion | More suitable for simple, slower, or less precise systems |
Main Components of a CNC Ball Screw System
A CNC ball screw system is not only the screw shaft and nut. It also includes recirculating balls, a return system, support bearings, coupling, lubrication, and the machine structure around it.
| Component | Role in CNC Machine | What to Check |
|---|---|---|
| Screw shaft | Converts motor rotation into axis movement | Diameter, lead, length, accuracy grade, and end machining |
| Ball nut | Moves along the screw and drives the CNC axis | Nut type, preload, flange size, return structure, and mounting space |
| Recirculating balls | Reduce friction between the screw and nut | Smooth circulation, lubrication, noise, and wear condition |
| Return system | Keeps balls circulating inside the nut | Speed, noise, stability, and nut structure |
| Support bearings | Support the screw ends and control axial movement | BK/BF, FK/FF, EK/EF support type, alignment, and bearing preload |
| Coupling | Connects the motor and screw shaft | Alignment, torque, backlash, and installation space |
How Does a Ball Screw Work in a CNC Machine?
The working principle is based on rolling instead of sliding. The motor rotates the screw shaft, and the helical groove guides the rolling balls between the screw shaft and the nut. The nut moves linearly and drives the CNC axis.
The balls do not simply roll once and stop. They continuously return through the ball return system inside the nut. This continuous circulation allows smooth linear movement over repeated CNC cutting cycles.
A ball screw mainly transmits axial force. In CNC machines, radial load and side load should normally be supported by linear guideways, guide blocks, or bearing structures. This separation helps the ball screw focus on accurate feed motion while the guide system supports cutting forces and machine rigidity.
Advantages of Ball Screws in CNC Machines
Ball screws are widely used in CNC machines because they meet several important motion requirements at the same time: efficiency, accuracy, repeatability, smoothness, and load stability.
1. High Efficiency
Rolling friction requires less torque than sliding friction. This helps CNC machines achieve smoother feed motion and better acceleration with less power loss.
2. Lower Backlash
With suitable preload, a CNC ball screw can reduce axial clearance and improve repeatability. This is important for contouring, pocketing, drilling, engraving, and repeated machining operations.
3. Better Positioning Accuracy
CNC machines depend on controlled axis movement. A properly selected and installed ball screw helps the machine reach the programmed position more consistently.
4. Stable Feed Motion
The rolling mechanism helps reduce stick-slip problems. This gives smoother movement during cutting, especially when the axis changes direction or moves at low speed.
5. Long Service Life
Lower friction usually means less wear and less heat. With correct lubrication, alignment, and protection, a ball screw can maintain stable CNC axis motion for a long time.
Types of Ball Screws Used in CNC Machines
Different CNC machines require different ball screw types. The suitable choice depends on positioning accuracy, load, machine size, speed, budget, and working environment.
| Ball Screw Type | Typical CNC Use | Selection Direction |
|---|---|---|
| C7 rolled ball screw | CNC routers, woodworking machines, engraving machines, general automation | Cost-effective for common CNC feed motion |
| C5 ground ball screw | Higher-precision CNC machines, inspection equipment, precision positioning axes | Selected when positioning accuracy is more demanding |
| Double nut ball screw | Axes requiring lower backlash and higher rigidity | Useful when preload and rigidity are important |
| Miniature ball screw | Small CNC machines, compact automation, desktop equipment | Suitable for limited space and lighter load |
Where Ball Screws Are Used in CNC Machines
Ball screws are commonly used on the main motion axes of CNC machines. Each axis has different load and movement requirements.
| CNC Axis | How Ball Screw Is Used | Key Requirement |
|---|---|---|
| X-axis | Moves the table or gantry horizontally | Long travel, smooth feed, repeatability, and proper support |
| Y-axis | Supports table or gantry movement across the machine width | Rigidity, alignment, and stable motion under cutting load |
| Z-axis | Moves the spindle up and down | Axial load, braking or holding force, low backlash, and vertical safety |
Basic Guide: How to Choose a Ball Screw for CNC Machine
Choosing a ball screw for a CNC machine does not need to start with complicated calculations. For early communication, buyers can first confirm several basic factors.
Screw diameter:
Larger diameters usually provide higher rigidity and lower deflection. Common CNC sizes include 12mm, 16mm, 20mm, 25mm, and larger sizes.
Lead or pitch:
A smaller lead usually gives finer positioning and stronger thrust. A larger lead allows faster movement but may reduce positioning resolution.
Accuracy grade:
C7 rolled ball screws are commonly used in CNC routers, woodworking machines, engraving machines, and general automation. C5 ground ball screws are usually selected for higher-precision CNC machines and demanding positioning applications.
Length and end machining:
The screw length and machined ends should match the machine travel, support units, bearing seats, coupling, and motor layout.
Preload:
Preload can reduce backlash and improve rigidity, but excessive preload may increase friction, heat, and motor load.
Support units:
BK/BF, FK/FF, and EK/EF support units are selected according to screw size, machine structure, and installation space.
DLY CNC Ball Screw Reference
DLY supplies C7 rolled ball screws and C5 ground ball screws for CNC machines, automation equipment, engraving machines, woodworking machines, and precision positioning systems.
DLY ball screw shaft material is S55C, and ball nut material is 20CrMo. For CNC applications, screw diameter, lead, accuracy grade, nut type, end machining, support units, and installation conditions should be confirmed together.
For a complete CNC motion system, the ball screw should also be checked together with linear guideways, guide blocks, coupling, motor, machine frame, lubrication, and protection conditions.
Conclusion
A ball screw in a CNC machine is one of the key components that converts motor rotation into accurate linear movement. It directly affects feed motion, positioning accuracy, repeatability, and long-term cutting stability.
Compared with lead screws, ball screws use rolling contact, which provides higher efficiency, lower friction, better repeatability, and longer service life in CNC motion systems.
For CNC machine selection, the ball screw should be matched with the machine load, axis direction, travel length, speed, accuracy grade, preload, support units, and installation structure.
Need Help Checking a CNC Ball Screw?
If you are confirming ball screw diameter, lead, accuracy grade, end machining, support unit, or CNC axis requirement, you can send the model, drawing, load, travel length, or machine application for reference.
WhatsApp: +86 16605788856
Email: dlyexport2@dlybearing.com
