Contents
1. Ball Screw Nuts: Designs and Features
Ball Screws consist of a screw shaft and a ball nut. Depending on the nut design, different priorities can be achieved: compact construction, high rigidity, easy installation, very high rotational speeds, or especially smooth and quiet operation. The nut geometry also influences how the nut is mounted and secured, how forces are absorbed, and in which machine designs it can best be integrated.
The three different nut geometries or nut types are explained in more detail below.
1.1 Single Flange Nut
A single-flange nut is a ball screw nut with only one flange. You can imagine it as a thick cylinder with a “disc” on one side:
- Cylinder: This is where the screw thread and balls run.
- Flange (“disc”): This is used to bolt the nut to a base plate, carriage, or machine component.
The flange usually has several through-holes or threaded holes for mounting screws. Through this flange, the nut is rigidly connected to the machine. As the screw shaft rotates or moves linearly, the nut converts the motion into linear movement of the carriage. Inside the nut, balls roll between the screw thread and the nut raceway. When the balls reach the end of their thread path, they are returned via a recirculation system (depending on the design type) and continue circulating.
Reasons for using a Single Flange Nut
When is a Single Flange Nut the right choice?
You can roughly ask yourself the following questions when making your selection:
✓ Yes, a single flange nut is a very good choice.
✘ No, I need double-sided support or very high preload stiffness → Consider a double flange nut instead.
✓ Yes, a single flange nut is a good fit because the flange only “protrudes” on one side.
✘ No, I have very limited space all around → in that case, a cylindrical nut integrated into the housing might be more suitable.
✓ Yes, a single flange nut is usually completely sufficient.
✘ No, very high forces or very high rigidity and preload are required → Consider a double flange nut or special heavy-duty variants.
✓ Yes, a single flange nut is often the first and most economical choice.
1.2 Double Flange Nut
A double-flange nut is a “two-row” ball screw nut with a shared flange plane. Imagine the cylinder with a flange again, just like the single flange nut, but with a longer nut body. Because of the greater length, more balls are in contact, which increases load capacity and rigidity.
- Long cylinder: this is where the thread and balls run
- The flange: used for mounting and support
The nut can be bolted, supported, or preloaded on both sides via its flange and cylindrical seating surface. This makes it especially rigid and suitable for higher demands.
The internal function is the same as that of the single flange nut. The difference lies in the mechanical connection: thanks to the longer nut body with flange, higher forces can be absorbed and transferred more rigidly into the machine frame or bearing supports. For example, the nut can be clamped between two support surfaces or mounted with preload using screws. This results in a very rigid, nearly backlash-free mounting of the nut within the system.
Reasons for using a Double Flange Nut
When is a Double Flange Nut the right choice?
You can roughly ask yourself the following questions when making your selection:
✓ Yes, the axis should deform as little as possible under load → prefer a double-flange nut.
✘ No, standard rigidity is sufficient → a single flange nut may be adequate.
✓ Yes, a double-flange nut is ideal, for example between two bearing plates or in a housing block.
✘ No, mounting on one side is sufficient → single flange nut.
✓ Yes, double-flange nut (possibly in combination with preloaded systems or heavy-duty series).
✘ No, single flange nut or cylindrical nut.
✓ Yes, typically a double-flange nut with a suitable interface to the motor.
✘ No, conventional, non-driven flange nuts are sufficient.
1.2 Cylindrical Nut
A cylindrical nut is a ball screw nut without a flange, essentially just a “cylinder.” The cylindrical nut is guided directly in a bore, sleeve, or housing. It's especially compact and well suited for confined installation spaces. Its internal function is identical to that of flange nuts; however, it's typically retained by a fitted seat rather than being bolted in place via a flange.
Reasons for using a Cylindrical Nut
When is a Cylindrical Nut the right choice?
You can roughly ask yourself the following questions when making your selection:
✓ Yes, a cylindrical nut is ideal.
✘ No, flange nuts are possible.
✘ No, a cylindrical nut is sufficient.
✓ Yes, a double-flange nut is the better choice.
✘ No, a cylindrical nut is sufficient.
✓ Yes, a double-flange nut is the better choice.
✓ Yes, a cylindrical nut is well suited for this.
✘ No, in this case, single-flange or double-flange nuts are better.
2. Deflection and circulation systems
Deflection and circulation systems ensure that the balls in a ball screw drive can continuously circulate instead of simply “falling out” of the front of the nut. The balls transfer the load between the screw shaft and the nut and must be guided back to the starting point after passing through the thread grooves. This is exactly what the deflection mechanism does.
Depending on the design, two things differ:
- Where the balls are returned (inside the nut, via end caps, via external tubes, etc.)
- How the raceway is designed (for compact design, high speed, heavy-duty loads, long strokes, etc.)
That is why different deflection and circulation systems exist. Some are especially compact and suitable for confined installation spaces. Others are optimized for high travel speeds and smooth running. Still others are designed for very high forces and heavy-duty applications.
Design considerations:
At the shaft end of the ball screw, at least one complete thread turn must be present. The shaft diameter at this end should be smaller than the root diameter of the raceway so that the ball nut can be easily mounted. If special requirements exist, a shaft sleeve can additionally be installed at this end of the thread after assembling the screw shaft and nut.
2.1 Internal circulation
In internal circulation systems (designations: FEIG, FDIG, DEIG, DDIG), the balls circulate inside the nut. The circulation elements are located within the nut contour and usually do not protrude significantly outward. Inside the nut sits a deflection plate. This ensures that the balls are guided out of the thread groove, redirected, and then returned into another thread groove.
Structure of Internal Circulation
A single-flange nut is a ball screw nut with only one flange. You can imagine it as a thick cylinder with a “disc” on one side:
- Cylinder: This is where the screw thread and balls run.
- Flange (“disc”): This is used to bolt the nut to a base plate, carriage, or machine component.
The flange usually has several through-holes or threaded holes for mounting screws. Through this flange, the nut is rigidly connected to the machine. As the screw shaft rotates or moves linearly, the nut converts the motion into linear movement of the carriage. Inside the nut, balls roll between the screw thread and the nut raceway. When the balls reach the end of their thread path, they are returned via a recirculation system (depending on the design type) and continue circulating.
Typical characteristics
Adaptable
The internal circulation system ensures stable and reliable operation during slow, fast, and frequent oscillating movements over short distances.
Small outer diameter
The outer diameter of the nut is small, making it suitable for ball screw pairs with small thread pitches. The DN limit value is 70,000.
Optimized smoothness of operation
By guiding the balls precisely through the deflection plate, impact points are reduced and changes in direction are performed smoothly.
Internal circulation: Sizes
2.2 End-cap circulation
In end-cap circulation systems (designations: FEEG, FDEG, DEEG, FEEH), the balls are deflected at the end of the nut’s raceway using end caps. The balls roll through the ball thread between the screw shaft and the nut. At the end of the nut, the balls reach an end cap - a component at the front face of the nut that contains special channels. There, a smoothly designed return channel guides the balls around the thread. Afterwards, they are returned to the beginning of the next thread turn. This creates a closed ball circulation system without the balls falling out of the nut.
You can imagine it like a miniature subway system, where the train is directed into a tunnel at the terminal station and returns to the track on the other side.
Structure of End-Cap Circulation
Typical characteristics
Low noise
Thanks to the smooth, flow-optimized return design, impact noise from the steel balls is significantly reduced.
High speed
The precise design of the end caps and the robust deflection material allow very high rotational speeds with DN values of up to 180,000.
Compact and lightweight
Due to the end-cap design, the overall shape of the nut can be 18–30% more compact compared to conventional circulation designs.
End-cap circulation: Sizes
2.2 Single Flange Nut with High Lead
This circulation type (designation: FEEU) uses single- and multi-start thread raceways with a very large thread lead. As a result, the nut travels a particularly large axial distance per one revolution of the screw shaft. A typical characteristic of this circulation type is a lead that is approximately 1 to 2 times the screw shaft diameter. This creates a system that is designed for high travel speeds.
The balls circulate back into the raceway via the internal circulation system, just like in a standard single flange nut — the difference therefore lies not in the type of circulation, but in the geometry of the raceway and the thread lead.
FEEU-Size
Typical characteristics
Travel speed
Due to the large lead per revolution, the axis can move significantly faster at the same rotational speed.
Heat-reducing
Since the nut travels a much greater distance per revolution, the screw shaft requires lower rotational speed to achieve the same feed velocity. The DN limit value is 100,000.
Large leads
Conventional ball screw drives can hardly achieve such large leads due to design limitations. This nut type is specifically designed for this, including appropriately shaped thread raceways and circulation geometries.
2.3 Tube Circulation
In tube circulation systems (designations: FEZG, FDZG, FEVG, FDVG), the balls are returned outside the nut through a curved tube. The balls roll within the thread groove between the screw shaft and the nut. At the end of the load-bearing raceway, they leave the groove and enter a circulating return tube. This tube guides the balls along the outside of the nut body. At the other end, they are reintroduced into the thread groove.
The return tube is usually mounted on the side or on top of the nut - easily recognizable as a characteristic, curved “loop.” The DN limit value for this design is 100,000.
Sketch drawing of tube circulation
Typical characteristics
Flexible combination
Tube circulation can be easily adapted to different screw shaft diameters, leads, and numbers of ball rows.
Wide range of applications
Since the return system is located externally, more complex or larger nut bodies can be designed without restricting the internal circulation mechanism.
Thread turns
Both ends of the screw shaft raceway can be designed with “incomplete threads.” This means the screw shaft does not necessarily need a complete thread turn, since the circulation system bridges the end of the raceway anyway.
Tube circulation: Sizes
2.4 Heavy Load Series
In the heavy load series (designation: FEKS), a deflection element guides the balls out of the thread once they reach the end of a thread turn. Unlike the classic tube circulation system, the return tube is not mounted externally on the nut but is integrated into the nut body. The channels are incorporated within the nut and are not attached externally.
Although it is a heavy load system, the smooth deflection geometry enables high rotational speeds of up to an impressive 150,000 DN.
FEKS series high-speed type steel ball with a retainer circulation
Typical characteristics
Maximized load capacity
Thanks to an optimized raceway profile, an ideally designed contact angle, and leads matched to the ball diameter, the heavy load series achieves exceptionally high load ratings.
High speed
The optimized ball return system of the FEKS high-performance design enables speeds of up to 150,000 DN, while significantly reducing running noise.
Long service life
The screw shafts are made from high-quality imported steels with threads that are fully induction-hardened. The nuts are manufactured from case-hardened special steel and receive a uniformly hardened raceway through vacuum carburizing.
FEKS-Size
2.5 Rotation Flange Nut
In the rotation flange nut (designations: FEIR, FDIR), the screw shaft doesn't rotate; only the nut produces the linear motion. The nut itself is connected to a drive (e.g., an electric motor or gearbox). The screw shaft remains axially fixed and can only rotate if it's driven by the nut.
By driving the nut instead of the screw shaft, the motion of the balls is generated without the screw having to rotate at high speed. This makes high-speed transmission possible, even with extra-long screw shafts.
FDIR-Size
Typical characteristics
High-speed transmission
Applications with long strokes can be realized without reaching the screw shaft’s limiting rotational speed.
Driving multiple nuts
Several nuts can be installed on the same screw shaft at the same time. Each nut can be driven by its own motor.
Simple screw shaft design
The screw shaft doesn't need to be supported in rotating bearings → no support bearings required. The screw end design is simpler: at least one end with a complete thread turn, and, if necessary, a shaft sleeve after assembly.
3. Overview
In conclusion, the selection of the appropriate circulation system is crucial for the performance, precision, and service life of a ball screw nut. Depending on the specific requirements, different solutions are used. Below is a brief overview:
- Internal circulation: Standard solution, space-saving, suitable for medium loads and speeds.
- End-cap circulation: Simple design, suitable for moderate loads and compact installation conditions.
- Single flange nut with high lead: High feed speed with low load.
- Tube circulation: High precision and smooth operation, ideal for sensitive applications.
- Heavy load series: Maximum load capacity, reliable even under large loads.
- Rotation flange nut: Combination of positioning accuracy and direct force transmission, e.g., in automated systems.
FAQs about High-Precision Ball Screws
These ball screw types are manufactured with reduced axial play and high dimensional accuracy. This allows them to be used in machining centers or other systems requiring high precision.
C7 to C1 are common. C3–C1 are used for positioning tasks, C7–C5 for transport applications. The key factors are your requirements for screw length, backlash, repeatability, and load.
High-Precision Ball Screws have tighter tolerances, less backlash, and higher rigidity. They’re suitable for precise positioning tasks, whereas Standard Screws are more suited for simple feed and transport movements.
Preload eliminates backlash and increases rigidity and precision. It’s essential for positioning tasks but less relevant for transport purposes.
Rolled: cold-formed, cost-effective, medium precision.
Ground: precision-ground, offering the highest accuracy.
Whirled: formed by chip removal, faster than the ground version and more precise than the rolled variant.
Heavy-load types feature robust raceways and large balls. High-speed types use larger leads and special deflectors.
Shaft diameters from 4–300 mm, leads from 1–80 mm, lengths up to 12,000 mm (single-piece), and up to 22,000 mm (multi-piece assemblies).
Screws are made of induction-hardened special steel. Nuts are made from vacuum-carburized steel. This ensures durability and load capacity.
Service life can be calculated theoretically based on the bearing life formula. It depends on speed, load rating, and axial force.
DN = diameter × rotational speed. This formula helps calculate the maximum speed of the nut.
Various deflection systems (internal, external), flange shapes, multiple nuts, compact versions, and special threads.
Positioning types are preloaded (low backlash), transport types have backlash and are simpler—but not suitable for precise movement. High precision is also reflected in the purchase price.
Yes, there are single, double, and custom nuts. Replacement is usually straightforward with standard parts, and conditionally possible with special designs.
Typically via lubrication holes for oil or grease. Regular lubrication is crucial for service life and smooth operation.
Lateral forces must be strictly avoided. There should be no overconstraint from the screw bearings. Always mount or dismount the nut using a sleeve—otherwise, the balls may fall out.
Yes. There are miniature ball screws and compact designs with small outer diameters and shortened nuts—ideal for tight installation spaces.
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