How to Improve the Efficiency of a Linear Ball Screw System

The most effective ways to improve linear ball screw efficiency are to maintain correct lubrication, align the screw and nut accurately, avoid excessive preload, reduce seal and bearing resistance, and keep the raceways free from contamination. Replacing the motor with a larger one may overcome resistance, but it does not correct the mechanical source of efficiency loss.

A correctly selected ball screw uses rolling contact and normally achieves much higher transmission efficiency than a sliding screw. However, the efficiency of the complete axis is lower than the theoretical efficiency of the screw-and-nut pair because the support bearings, seals, coupling, guideways and installation alignment also consume torque.

What Does Ball Screw Efficiency Mean?

Ball screw efficiency describes how much of the input rotational power is converted into useful linear output. For a screw driving an axial load, the approximate mechanical efficiency can be calculated from:

Use the same system of units throughout the calculation. Input torque should be the torque required at the screw shaft under a stable operating condition-not the motor's maximum rated torque.

Theoretical efficiency and measured machine efficiency are not always the same. The measured torque can include:

• Ball nut preload torque
• Seal and lubricant resistance
• Fixed- and supported-end bearing friction
• Coupling losses
• Guideway and table resistance
• Misalignment between the screw, nut and support bearings
• Acceleration of the rotating and moving components

For meaningful comparison, measure the torque at the same load, speed, temperature and travel position.

1. Use the Correct Lubricant and Quantity

Lubrication separates the rolling contact surfaces, reduces wear and helps the balls circulate smoothly. Both insufficient and excessive lubrication can increase operating torque.

Too little lubricant can cause metal-to-metal contact, rising temperature, noise and raceway wear. Too much grease can create churning resistance, especially at low temperature, during startup or at high rotational speed.

To maintain efficient operation:

• Use grease or oil suitable for ball screws, speed, load and temperature.
• Do not mix incompatible lubricant types.
• Clean the lubrication port before adding lubricant.
• Apply the specified quantity instead of filling the nut completely.
• Move the nut through the stroke after lubrication to distribute the lubricant.
• Adjust the relubrication interval according to operating time and contamination level.

If running torque increases immediately after relubrication, check whether too much grease was added or whether the new lubricant is incompatible with the previous lubricant.

2. Align the Screw, Nut Housing and Support Bearings

Installation misalignment is one of the most common causes of unnecessary resistance. A ball screw is designed primarily to transmit axial force. If the nut housing pulls the nut sideways, the balls carry an additional radial load and the running torque becomes uneven.

A practical alignment procedure is:

1. Install the fixed-end and supported-end units without forcing the screw into position.
2. Check that the screw can rotate smoothly before connecting the nut housing.
3. Attach the nut housing or moving table with the mounting bolts initially loose.
4. Move the table slowly through the available stroke.
5. Allow the nut housing to settle into its natural aligned position.
6. Tighten the nut-housing bolts gradually and recheck the running torque.

3. Do Not Use More Preload Than the Application Requires

Preload reduces axial clearance and improves rigidity during direction reversal. It is valuable in precision positioning systems, but preload does not improve transmission efficiency by itself.

A higher preload increases the internal contact force between the balls and raceways. This raises starting torque and running torque, and may increase heat during continuous operation.

Select preload according to:

• Required axial rigidity
• Permissible backlash or lost motion
• Direction-reversal frequency
• External axial load
• Motor torque margin
• Expected operating temperature

For general automation where normal axial clearance is acceptable, an SFU single-nut ball screw may provide lower drag than a heavily preloaded double-nut structure. Higher preload should be selected only when the required rigidity and reversal stability justify the additional torque.

4. Select a Suitable Diameter and Lead

Screw diameter and lead affect load capacity, rigidity, rotational speed and drive torque. A larger screw is not automatically more efficient, and the smallest available lead is not always the best choice.

A smaller lead produces more axial thrust from the same input torque and provides finer travel per revolution. A larger lead produces more linear travel per revolution and may reduce the motor speed needed for a specified linear speed.

The selection should balance:

• Required linear speed
• Required axial thrust
• Motor speed and torque
• Positioning resolution
• Screw length and critical speed
• Buckling resistance
• Available installation space

An oversized screw increases rotating inertia and may require more acceleration torque. An undersized screw can deform, vibrate or operate too close to its load and speed limits. Neither condition produces an efficient motion axis.

5. Match the Ball Screw to the Real Load Range

Efficiency is often discussed as a fixed percentage, but actual drive torque changes with load. At a very light axial load, seal resistance, lubricant drag and preload torque can represent a large share of the total input torque.

At a high load, raceway contact deformation and support-bearing load become more important. The ball screw should therefore be selected from the real continuous load, peak load, duty cycle and acceleration-not only the maximum motor torque.

DLY's linear motion ball screw range includes C7 rolled and C5 ground options for different motion and positioning requirements, with custom length and shaft-end machining according to drawings.

6. Reduce Support-Bearing Resistance

The support units are part of the rotating system. Incorrect bearing preload, unsuitable bearing selection or inaccurate shaft-end machining can increase friction even when the ball nut operates normally.

Check the following points:

• The fixed-end bearing arrangement matches the axial load and rotational speed.
• The supported end is not locked in a way that prevents thermal expansion.
• The bearing journals are concentric with the screw axis.
• The locknut is tightened according to the support design.
• The bearings are not contaminated or damaged.
• The support housings are aligned with each other.

DLY supplies BK/BF, FK/FF and EK/EF ball screw support units. The support model must match the ball screw diameter, shaft-end dimensions, load and mounting structure.

7. Keep the Screw and Ball Return System Clean

Dust, chips and hardened lubricant increase resistance and can damage the raceways or ball-return components. Contamination is especially serious in woodworking, machining, grinding and cutting equipment.

Use suitable protection such as bellows, covers, scrapers or an enclosed axis where necessary. Do not rely on the ball nut seals as the only protection against large chips or abrasive dust.

When cleaning:

• Remove loose contamination without pushing it into the nut.
• Use a cleaning method compatible with the seals and lubricant.
• Do not rotate a contaminated nut repeatedly in an attempt to make it run smoothly.
• Relubricate the raceway after cleaning.
• Inspect the seals and ball-return components for damage.

8. Check the Coupling and Motor Connection

A flexible coupling can accommodate a limited amount of installation error, but it should not be used to correct major offset or angular misalignment. Excessive coupling deformation increases torque loss and applies unwanted radial force to the screw and motor bearings.

Confirm that:

• The motor shaft and ball screw shaft are aligned within the coupling requirement.
• The coupling bore matches both shaft diameters.
• The clamping screws are tightened correctly.
• The coupling is rated for the required torque and speed.
• The two shaft ends do not press against each other inside the coupling.

If the screw runs smoothly when disconnected from the motor but becomes tight after coupling installation, inspect the motor position and coupling alignment.

9. Control Operating Temperature

Temperature changes lubricant viscosity, preload, bearing condition and screw length. Grease becomes more resistant at low temperature, while excessive temperature can reduce lubricant life and change the dimensional condition of a precision axis.

For equipment requiring stable positioning, allow the axis to reach a consistent operating temperature before checking accuracy. A sudden increase in temperature or drive torque can indicate excessive preload, insufficient lubrication, bearing problems or installation misalignment.

Existing DLY Ball Screw Examples

Ball screw efficiency depends on the complete assembly, including the screw, nut, support and installation alignment.

Diameter, lead and nut structure should be selected according to load, speed and positioning requirements.

How to Find the Source of Efficiency Loss

The most useful efficiency check is not simply whether the motor can move the axis. Record running torque, starting torque, temperature and travel position under repeatable conditions. A change in these values can reveal lubrication, alignment or bearing problems before severe damage occurs.

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