Ball screw selection should not start only from a model number such as 1605, 2005, or 2510. A suitable ball screw selection should begin with the machine application, load direction, travel length, speed, accuracy requirement, nut structure, end machining, and support method.
For CNC machines, automation equipment, packaging systems, lifting axes, and precision positioning devices, choosing the right ball screw assembly can improve accuracy, repeatability, service life, and long-term machine stability.
This guide explains 9 key factors to consider when choosing a ball screw, including application requirements, screw diameter, lead, load capacity, accuracy grade, preload, nut type, end machining, support units, and working environment.
Tip 1: Start from the Application, Not Only the Model Number
A ball screw model should be selected according to how the machine actually works. The same diameter and lead may perform differently in a CNC router, lifting device, packaging machine, medical device, or high-speed automation axis.
Before choosing a ball screw, confirm the machine type, movement direction, load weight, travel length, required speed, positioning accuracy, installation space, and expected duty cycle. These factors determine whether the machine needs a standard rolled ball screw, a higher-precision ground ball screw, a preloaded nut, or special end machining.
Practical idea:
Do not select a ball screw only because the model is common. Select it because the diameter, lead, accuracy grade, nut structure, and end support match the real application.
Tip 2: Confirm Ball Screw Diameter
The ball screw diameter affects load capacity, rigidity, shaft deflection, critical speed, and long-term stability. A larger diameter usually provides higher rigidity and better support for longer travel or heavier load.
For compact machines and light loads, smaller diameters such as 12mm or 16mm may be enough. For CNC machines, industrial automation, and longer axes, 20mm, 25mm, 32mm, or larger diameters may be more suitable depending on load and stroke.
If the screw is too small for the load or travel length, it may bend, vibrate, or run close to its critical speed limit. If the screw is much larger than needed, cost, inertia, and motor requirement may increase.
Tip 3: Choose the Right Lead
The lead of a ball screw refers to the linear distance the nut moves when the screw rotates one full turn. For example, a 1605 ball screw usually means 16mm diameter and 5mm lead.
A smaller lead provides better positioning resolution and higher thrust under the same motor torque. A larger lead allows faster linear movement but may reduce thrust and positioning resolution.
| Parameter | What It Affects | Selection Note |
|---|---|---|
| Diameter | Rigidity, load capacity, shaft deflection, and critical speed | Use larger diameter for higher load, longer travel, or stronger rigidity needs |
| Lead | Speed, thrust, positioning resolution, and motor torque demand | Use smaller lead for fine positioning; larger lead for faster movement |
| Length | Critical speed, buckling risk, support method, and installation alignment | Long screws need suitable support units and careful alignment |
Tip 4: Check Load Capacity and Installation Direction
Load is one of the most important points in how to choose a ball screw. Buyers should check not only the load weight, but also whether the axis is horizontal, vertical, inclined, or affected by moment force.
For horizontal axes, the ball screw mainly moves the load along the guide system. For vertical axes, the ball screw must support the weight directly, and back-driving, braking, motor torque, and safety margin become more important.
The life expectancy should also be estimated according to the real operating profile, such as working hours per day, travel cycles, speed changes, acceleration, and load variation. More demanding applications may need a larger diameter, stronger nut, or different support method.
Load-related checks:
Confirm horizontal load, vertical load, or inclined movement.
Check whether the load changes during acceleration and deceleration.
Check whether the nut is mainly under tension or compression.
For long screws under compression, consider buckling risk and support method.
Tip 5: Match Accuracy Grade: C7 Rolled or C5 Ground
Accuracy grade should match the actual positioning requirement. For many general motion systems, a C7 rolled ball screw is enough. For high-precision positioning, a C5 ground ball screw may be needed.
For DLY products, cold-rolled ball screws are usually C7 accuracy grade, while ground ball screws are C5 accuracy grade. The choice should depend on machine accuracy requirement, repeatability, budget, and whether external feedback is used.
| Item | C7 Rolled Ball Screw | C5 Ground Ball Screw |
|---|---|---|
| Manufacturing Method | Cold rolled | Precision ground |
| Typical Use | General CNC, automation, packaging, woodworking, common positioning axes | Precision CNC, inspection equipment, laboratory systems, high-accuracy positioning |
| Main Advantage | Cost-effective and stable for common motion needs | Higher positioning accuracy and better lead accuracy |
| DLY Direction | Cold-rolled ball screws are C7 | Ground ball screws are C5 |
Tip 6: Decide Whether Preload Is Needed
Repeatability is affected by backlash, which is the axial play between the ball screw and nut. Preload can reduce backlash and improve rigidity, but it also increases friction, heat, and required driving torque.
The original article mentioned that without preload, axial play may be around 0.002 to 0.008 inches, or about 0.06 to 0.2 mm, depending on size. Preloaded nuts can reduce axial play and improve stiffness, but the preload level should be chosen carefully.
| Preload Condition | Possible Result | Selection Note |
|---|---|---|
| No or low preload | Possible backlash, lower rigidity, lower friction | Suitable for many transport or cost-sensitive applications |
| Suitable preload | Lower axial clearance, better rigidity, more stable repeatability | Suitable for precision positioning and CNC applications |
| Excessive preload | Higher friction, heat generation, motor load, and faster wear | Avoid selecting high preload without checking speed and torque |
Tip 7: Choose the Right Ball Nut Type
The ball nut affects installation method, load capacity, preload, return structure, and available space. Common nut types include flanged nuts, double nuts, compact nuts, cylindrical nuts, and customized nut structures.
The ball return system also matters. External return tubes are often cost-effective and easier to maintain, while internal return systems can be more compact and may reduce noise and radial protrusion. The suitable choice depends on lead, speed, load, nut size, and machine layout.
For machines with limited installation space, the nut flange size, nut body diameter, mounting holes, and lubrication access should be checked before ordering.
Tip 8: Confirm End Machining and Support Units
End machining should be confirmed before production because it affects bearing installation, coupling connection, motor alignment, support accuracy, and final assembly performance.
Common end machining details include bearing seat diameter, shoulder position, thread, keyway, circlip groove, coupling end, and total processed length. If any dimension is wrong, the ball screw may not fit the support unit or machine frame.
Support units such as BK/BF, FK/FF, and EK/EF are commonly selected according to screw diameter, installation space, and machine structure. Fixed-end and supported-end arrangements directly affect critical speed, column strength, and alignment difficulty.
For long ball screws, end support selection is especially important. A fixed-fixed support arrangement can provide better support for higher speed and longer travel, while simpler support arrangements may be easier to install but have lower critical speed and rigidity.
Tip 9: Consider Speed, Stroke, Environment, and Maintenance
The final selection should also check speed, stroke length, vibration, environment, lubrication, and maintenance. A long screw running at high speed may reach critical speed and produce vibration or resonance.
The original article gave an example: a 100-inch-long ball screw with a 1-inch root diameter may have a natural frequency of about 18 Hz when fixed at both ends, but about 8 Hz when both ends are supported. This shows why end support method and unsupported length matter in high-speed applications.
Environment also affects ball screw service life. Dust, chips, humidity, coolant, poor lubrication, or incompatible grease can increase wear, noise, corrosion, and maintenance cost.
Handling and maintenance notes:
Keep ball screws packed, lubricated, and stored in a clean and dry place before installation.
Avoid shock, bending, or impact during handling.
Check lubrication regularly and confirm grease compatibility before relubrication.
Inspect raceways for wear, spalling, indentation, contamination, and corrosion.
Any change in noise level or running feel may indicate internal wear or installation problems.
Ball Screw Selection Summary Table
| Selection Factor | What to Check | Why It Matters |
|---|---|---|
| Application | CNC, automation, packaging, medical, lifting, positioning, etc. | Different machines require different accuracy, load, speed, and nut structure |
| Diameter | 12mm, 16mm, 20mm, 25mm, 32mm, etc. | Affects rigidity, load capacity, shaft deflection, and critical speed |
| Lead | 4mm, 5mm, 10mm, 20mm, etc. | Affects speed, thrust, and positioning resolution |
| Accuracy Grade | C7 rolled or C5 ground | Affects positioning accuracy, repeatability, and cost |
| Nut Type | SFU, DFU, SFI, SFE, compact or custom nut | Affects installation, preload, load capacity, and structure design |
| Preload | Standard clearance or preloaded nut | Affects backlash, rigidity, friction, heat, and motor torque |
| End Machining | Bearing seat, thread, keyway, coupling end, support unit fit | Affects final assembly accuracy and support bearing life |
| Support Unit | BK/BF, FK/FF, EK/EF or custom support structure | Affects axial rigidity, critical speed, and installation stability |
| Environment | Dust, chips, coolant, humidity, corrosion risk | Affects lubrication, seals, coating, and service life |
Before Ordering Checklist
Before ordering a ball screw assembly, it is better to confirm the key parameters clearly. This can reduce communication time and avoid wrong model selection.
Screw diameter and lead.
Total length and effective travel length.
Accuracy grade: C7 rolled or C5 ground.
Ball nut type and mounting direction.
End machining drawing or support unit type.
Load, speed, horizontal or vertical installation.
Application machine and working environment.
DLY Ball Screw Selection Reference
DLY supplies ball screws, matched ball nuts, customized end machining, ball screw supports, and related linear motion components for CNC machines, automation equipment, packaging machinery, and industrial motion systems.
For practical selection, screw diameter, lead, nut type, accuracy grade, preload, end machining, support unit, load, speed, and machine application should be confirmed together. DLY cold-rolled ball screws are generally C7 accuracy grade, and ground ball screws are C5 accuracy grade.
Conclusion
A suitable ball screw should be selected according to application requirements, not only by a common model number. Diameter, lead, load capacity, speed, accuracy grade, preload, nut type, end machining, support unit, and working environment all affect final machine performance.
For general CNC and automation applications, C7 rolled ball screws are often practical and cost-effective. For higher-precision positioning systems, C5 ground ball screws may be more suitable. For long travel, vertical installation, or high-speed axes, support method, buckling, critical speed, and maintenance should also be checked carefully.
A complete ball screw selection should consider the screw, nut, support, end machining, lubrication, and machine structure as one system.
Need Help Checking Ball Screw Selection?
If you are confirming ball screw diameter, lead, nut type, accuracy grade, end machining, or support unit, you can send the model, drawing, load, travel length, or machine application for reference.
Email: export@dlybearing.com
