Can a Ball Nut Run at High Speed? DN Value, Lead & Heat Explained

Yes, a ball nut can be used in a high-speed application, but the correct question is not simply whether the nut can "move fast."

For a high-speed ball screw axis, engineers must check required screw RPM, DN or Dm-N value, ball circulation design, lead, lubrication, preload, heat generation and operating duty. At the same time, the rotating screw shaft must remain below its allowable critical speed.

These are different limits. A ball nut may have a circulation system capable of high speed while the screw shaft itself is already approaching resonance. Conversely, a short and rigid screw may have plenty of critical-speed margin while the ball nut reaches its DN or thermal limit first.

What Does "High Speed" Mean for a Ball Nut?

High linear speed and high rotational speed are related, but they are not the same thing.

The relationship is:

Screw RPM = Linear Speed ÷ Lead

When linear speed is expressed in mm/min and lead in mm/rev, the result is screw revolutions per minute.

For example, suppose an axis must travel at 30 m/min, or 30,000 mm/min.

Ball Screw Lead	Required RPM at 30 m/min
5 mm	6,000 rpm
10 mm	3,000 rpm
20 mm	1,500 rpm
25 mm	1,200 rpm

This illustrates why high-lead ball screws are often used for fast linear travel. A larger lead allows the same linear speed to be reached at a lower rotational speed.

However, high lead does not automatically mean high-speed capability. The nut circulation system, screw shaft, support bearings, lubrication and preload must still be suitable for the required operating speed.

The Ball Nut Has a Speed Limit of Its Own

Inside a ball nut, steel balls do not simply roll along an endless straight path.

They travel through the loaded raceway between the screw and nut, leave the loaded zone, pass through a return path and re-enter the raceway.

As rotational speed increases:

• the balls circulate through the nut more frequently;
• ball acceleration inside the return system increases;
• impact at the transition into and out of the return path becomes more important;
• lubrication becomes more difficult to maintain;
• frictional heat increases;
• noise and vibration can increase;
• centrifugal and inertial effects become more significant.

This is why circulation design matters greatly in a high-speed ball nut.

What Is DN or Dm-N Value?

DN or Dm-N value is commonly used to describe the speed capability of a ball screw nut and its ball circulation system.

In simplified form:

DN = Reference Diameter × Rotational Speed

or, for catalogs using the ball pitch-circle diameter:

Dm-N = Dm × N

where:

• Dm = specified reference or ball pitch-circle diameter;
• N = rotational speed in rpm.

One important detail is that manufacturers do not always use exactly the same reference diameter when publishing DN or Dm-N limits.

Therefore, do not calculate a value using nominal screw diameter and directly compare it with a manufacturer's Dm-N limit unless both values use the same definition.

A Simple DN Example

For preliminary comparison only, suppose nominal screw diameter is used as the reference.

A 25 mm ball screw rotating at 4,000 rpm gives:

25 × 4,000 = 100,000

If rotational speed increases to 6,000 rpm:

25 × 6,000 = 150,000

Notice that increasing screw diameter does not automatically solve a DN-limit problem. At the same rpm, a larger reference diameter actually produces a higher DN value.

If nut speed becomes the limiting factor, possible solutions include:

• using a larger lead to reduce the required rpm;
• selecting a nut circulation structure designed for a higher DN/Dm-N value;
• reducing the target linear speed;
• reviewing preload and lubrication;
• considering another drive arrangement for extremely long or fast axes.

Critical Speed and Ball Nut Speed Limit Are Not the Same

This distinction is one of the most important points in high-speed ball screw selection.

Limit	Main Component	Main Failure Concern	Main Influencing Factors
DN / Dm-N limit	Ball nut and recirculation system	Heat, impact, noise and excessive ball-circulation speed	Nut design, reference diameter, RPM, ball return structure and lubrication
Critical speed	Rotating screw shaft	Resonance, whipping and lateral vibration	Root diameter, unsupported length and end-support condition

A long, slender ball screw is often limited by shaft critical speed before the nut reaches its maximum circulation capability.

A short, large-diameter screw can behave differently: the shaft may have a high critical speed, while DN/Dm-N or temperature becomes the practical limit.

For the shaft-side calculation, see Critical Speed of Ball Screw: How to Calculate It and Why It Matters.

Why Does Ball Circulation Design Matter at High Speed?

Every time a ball leaves the loaded raceway and enters the recirculation path, its direction and velocity change.

At low or moderate speed, these transitions are relatively easy to manage. At high rotational speed, repeated acceleration and impact can become a major source of:

• noise;
• vibration;
• heat;
• ball wear;
• return-component stress.

High-speed nut structures therefore focus not only on low friction but also on making ball return as smooth as possible.

End-cap and other optimized circulation structures can be useful because the ball path can be designed to reduce abrupt changes in ball movement.

SFS and SFE Solve Different High-Speed Problems

DLY supplies several ball nut structures. Two series frequently associated with faster motion are SFS and SFE, but they should not be treated as identical.

Series	Main Design Direction	Why It Can Help at Higher Speed
SFS	Silent-type single nut with end-cap circulation and compact structure	Smooth ball return and lower-noise operation for suitable medium-to-high-speed axes
SFE	High-lead flange nut	Larger travel per revolution allows high linear feed at lower screw RPM

DLY SFS nuts use an end-cover circulation structure and are available in larger-lead combinations such as 10, 20, 32, 40 and 50 mm depending on the model. They are selected when smooth circulation, compact installation and lower operating noise are important.

SFE nuts are primarily characterized by their large-lead design. Models such as SFE1616, SFE2020 and other high-lead configurations can achieve greater travel per screw revolution.

Therefore:

The actual maximum speed of either series must still be confirmed for the selected diameter, lead and operating condition.

High Lead Does Not Mean Unlimited Speed

A high-lead ball nut can reduce screw rpm substantially, but there are tradeoffs.

Larger Lead Effect	Result
More linear travel per revolution	Higher linear speed at the same RPM
Lower RPM for the same feed speed	Can help with critical-speed and DN limits
Greater travel per motor revolution	Coarser theoretical linear resolution for the same encoder resolution
Different helix geometry	Motor torque and drive requirements must be checked

This means the correct lead should be selected from the complete machine requirement, not simply by choosing the largest available lead.

Lubrication Becomes More Critical as Speed Increases

High-speed operation increases the number of rolling contacts and ball circulation cycles per unit time.

If lubrication is insufficient, the system can experience:

• higher friction;
• rapid temperature rise;
• raceway wear;
• ball wear;
• increased noise;
• shortened service life.

But more lubricant is not automatically better.

Excess grease can increase churning resistance inside the nut, particularly at higher speeds. This can increase torque and temperature instead of improving operation.

High-speed lubrication therefore needs the correct:

• lubricant type;
• viscosity;
• quantity;
• relubrication interval;
• supply method.

The appropriate solution depends on speed, load, duty cycle, nut structure, operating temperature and environment.

Why Does a High-Speed Ball Nut Generate Heat?

A ball screw is efficient, but it is not friction-free.

At high speed, heat can come from:

• ball-to-raceway rolling and sliding;
• ball-to-ball interaction;
• ball return transitions;
• seals and wipers;
• lubricant churning;
• preload;
• support bearings.

Temperature matters because the screw shaft expands as it heats.

Thermal expansion can then influence positioning accuracy, particularly on long precision axes.

For a high-speed precision machine, simply proving that the nut "can rotate at the required rpm" is therefore not enough. The thermal behavior of the complete axis should also be checked under realistic duty-cycle conditions.

Does More Preload Help at High Speed?

Preload can reduce axial clearance and increase rigidity, which is useful for precision positioning.

However, preload also increases internal contact force.

At high speed, excessive preload can contribute to:

• higher running torque;
• additional heat generation;
• greater lubrication demand;
• higher bearing and raceway stress;
• shorter life if operating conditions are not suitable.

Therefore, maximum preload is not automatically the best choice for a high-speed axis.

The appropriate preload should balance:

Rigidity + Backlash + Speed + Heat + Life

Load Still Matters at High Speed

A ball nut can satisfy its speed requirement and still be unsuitable because of load.

High-speed automation frequently combines:

• rapid acceleration;
• rapid deceleration;
• frequent reversing;
• short cycle times;
• continuous operation.

Acceleration creates additional inertia force:

F = m × a

This force must be included together with the normal working load when evaluating the ball screw's equivalent dynamic load and service life.

A high-speed pick-and-place axis with a relatively light payload can still experience significant dynamic load if acceleration is aggressive.

High Speed and High Accuracy Are Different Requirements

Another common mistake is assuming that the fastest ball nut must also be the most accurate.

Speed capability and positioning accuracy are separate specifications.

Accuracy depends on factors such as:

• ball screw accuracy grade;
• lead error;
• preload or axial clearance;
• support-bearing rigidity;
• installation alignment;
• thermal expansion;
• motor and encoder resolution;
• machine structural rigidity.

For example, selecting a high-lead SFE structure may help an axis reach a high feed rate at lower rpm, but the required C3, C5 or C7 accuracy grade must still be selected separately according to positioning requirements.

Do Not Ignore the Support Bearings

The ball nut is not the only rotating-system component with a speed limit.

The fixed-end support bearings must also tolerate:

• required RPM;
• axial preload;
• axial operating load;
• temperature;
• lubrication;
• continuous duty.

A ball nut capable of high-speed circulation provides no benefit if the support bearing or coupling becomes the actual speed limit.

The motor, coupling, fixed-side bearing unit, supported-side bearing and screw shaft should therefore be checked as one drive system.

Long Ball Screws Have a Different High-Speed Problem

For a long axis, screw shaft critical speed often becomes more restrictive.

Critical speed decreases rapidly as unsupported screw length increases. A long shaft can begin to whip even though the nut itself is still comfortably below its DN limit.

Possible solutions include:

• increasing screw root diameter;
• reducing unsupported length;
• using a more rigid end-support arrangement;
• increasing lead to reduce required RPM;
• using intermediate support where the machine design permits;
• considering a rotating-nut arrangement for very long high-speed axes.

For a complete system-level discussion, see How to Select a Ball Screw for High-Speed Operation.

When Does a Rotating Ball Nut Make Sense?

In a conventional ball screw axis, the screw shaft rotates while the nut moves linearly.

For a very long, high-speed axis, this can create a fundamental problem: the longer screw shaft must rotate at high rpm, making critical-speed control increasingly difficult.

A rotating-ball-nut system reverses this arrangement. The screw shaft remains stationary while the nut assembly rotates and travels along the screw.

This can be useful when:

• travel is very long;
• target feed speed is high;
• rotating-shaft critical speed is the main limitation;
• the machine structure can accommodate a rotating-nut drive unit.

However, this is a different mechanical architecture and requires a dedicated nut bearing, housing and drive arrangement. It is not created simply by taking an ordinary ball nut and rotating it.

What About DLY High-Speed Ball Screw Assemblies?

DLY also supplies high-speed ball screw assemblies for applications where higher rotational speed, low noise and stable acceleration are required.

The current DLY high-speed series is designed around an optimized ball-return structure and publishes a high Dm-N capability above 220,000 for the applicable series.

This does not mean every DLY ball nut or every screw diameter can automatically operate at the same RPM. The actual allowable speed must still be confirmed for the selected:

• series;
• diameter;
• lead;
• nut structure;
• screw length;
• support arrangement;
• load;
• preload;
• lubrication condition.

Example: Selecting Lead for a 24 m/min Axis

Suppose an automation axis needs a maximum linear speed of:

24 m/min = 24,000 mm/min

Compare three possible leads:

Lead	Required Screw RPM	Initial High-Speed Assessment
5 mm	4,800 rpm	High rotational speed; critical speed and DN require careful checking
10 mm	2,400 rpm	More manageable RPM, depending on diameter and screw length
20 mm	1,200 rpm	Much lower RPM, potentially helpful for long or fast axes

This does not prove that the 20 mm lead is automatically the best choice.

The designer must still check:

• motor torque;
• acceleration;
• positioning resolution;
• axial load;
• ball nut size;
• critical speed;
• DN/Dm-N limit;
• required precision.

But it demonstrates why lead is one of the first parameters to review when required feed speed is high.

Signs That a Ball Nut Is Struggling at High Speed

During machine testing, watch for changes that appear only as speed increases.

Symptom	Possible Cause
Nut temperature rises rapidly	Excess preload, lubrication problem, excessive speed or misalignment
Noise increases sharply with RPM	Ball circulation, lubrication, support bearing or resonance issue
Vibration appears at a specific RPM	Possible screw critical-speed resonance or system resonance
Motor current rises as speed increases	Increasing friction, lubricant churning, preload or alignment problem
Position changes as machine warms up	Thermal expansion of screw and machine structure
Seal or return component wear	Speed, contamination or lubrication condition may be unsuitable

Do not diagnose every high-speed vibration as a ball nut problem. Screw critical speed, support bearings, coupling alignment and machine structure should also be inspected.

How to Select a Ball Nut for High-Speed Operation

A practical selection process is:

1. Define the required linear speed. Use the actual maximum feed requirement rather than simply saying "high speed."
2. Select a preliminary lead. Convert linear speed into required screw RPM.
3. Check screw critical speed. Consider screw root diameter, unsupported length and end-support configuration.
4. Check DN or Dm-N. Use the definition and limit supplied for the selected ball nut series.
5. Select the circulation structure. Consider SFS or another high-speed/low-noise structure when ball return becomes important.
6. Evaluate a high-lead structure. SFE or another suitable high-lead series can reduce required screw RPM.
7. Check load and acceleration. Include inertia forces from rapid start-stop motion.
8. Select preload carefully. Use only as much preload as the rigidity and backlash requirement needs.
9. Confirm lubrication. Select lubricant type, quantity and interval for the actual speed and duty cycle.
10. Check support bearings and coupling. They must also satisfy the required RPM.
11. Check thermal behavior. For precision axes, consider screw expansion and operating temperature.
12. Run a realistic test cycle. Measure noise, temperature, torque and positioning behavior under actual operating conditions.

What Information Should You Send to DLY?

If you need a ball screw or ball nut for a high-speed axis, provide:

• required maximum linear speed;
• travel length;
• total screw length;
• preferred screw diameter, if already selected;
• lead;
• moving mass;
• maximum axial load;
• acceleration and deceleration;
• duty cycle;
• required positioning accuracy;
• required preload or backlash;
• end-support arrangement;
• motor speed;
• operating environment;
• installation drawing.

With these parameters, the selection can be checked as a complete system instead of choosing a nut only because its product description says "high speed."

Conclusion

Ball nuts can operate at high speed, but there is no universal RPM that applies to every ball nut.

The correct high-speed limit depends on the nut circulation structure, DN or Dm-N capability, diameter, lubrication, preload, load and thermal conditions.

At the same time, the screw shaft has a separate critical-speed limit that depends mainly on root diameter, unsupported length and support arrangement.

A reliable high-speed selection should therefore evaluate:

For fast linear motion, a larger lead can reduce required screw RPM. SFE series can be considered where high lead is the main requirement, while SFS and dedicated high-speed structures are useful when smooth ball circulation and lower-noise operation become more important.

The best solution is not simply the "fastest ball nut." It is the ball screw assembly that reaches the required linear speed while remaining within its mechanical, thermal and life limits.

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