Contents
High-Precision Ball Screws
Basics
1. What is a Ball Screw?
A Ball Screw is a mechanical component that converts rotary motion into linear motion – or vice versa. Small steel balls run between the screw shaft and the nut, making the movement especially low-friction and precise. The key advantages: virtually no wear, extremely high efficiency (up to 98% efficiency), and pinpoint positioning.
Ball Screw nut from the inside
2. High-Precision vs. Standard Ball Screws: What’s the difference?
Standard Ball Screws are often used for transport tasks where accuracy down to a hundredth of a millimeter isn't critical. They have backlash, simpler manufacturing, and looser tolerances — but they’re also more cost-effective.
High-Precision Ball Screws, on the other hand:
- have very tight manufacturing tolerances
- are often backlash-free (preloaded)
- are finely ground or whirled
- operate reliably with micrometer-level accuracy
In short: High-Precision Ball Screws are the “precision tools” among Ball Screws.
The lower the friction (μ) and the greater the lead angle, the higher the efficiency. A comparison of Ball Screws and Trapezoidal Screws.
3. How a Ball Screw works
The balls roll in a closed circuit between the screw shaft and the nut. When the screw rotates, the nut moves linearly – or vice versa. Depending on the application, there are two basic functions:
- Function A: Rotation of the screw → linear movement of the nut
- Function B: Linear movement of the screw → rotation of the nut
Thanks to the rolling motion, energy loss is minimal, and the movement is smooth and precise.
4. Manufacturing methods: rolled, whirled, ground
There are three ways to manufacture a Ball Screw – depending on the application and the required precision:
4.1 Rolled – cost-effective and fast
The thread is formed by cold rolling. This saves time and money but offers lower precision. It’s ideal for basic applications with moderate loads.
Typical for:
- Series production with moderate requirements
- Applications where some backlash is acceptable
- Tolerance classes like C7
4.2 Ground – the precision marvel
In this process, the thread is ground – the most elaborate but also the most precise method. It produces extremely smooth surfaces and exceptional dimensional accuracy. However, it’s also the most expensive option.
Typical for:
- CNC machines, precision axes
- Positioning drives in medical technology
- Tolerance classes T3 and better
4.3 Whirled – the middle ground
A cutting process where a rotating tool precisely shapes the thread. It’s more accurate than the rolled version and more affordable than the ground variant—an ideal compromise.
Typical for:
- Applications with higher demands
- Good surface quality and tight tolerances
- Tolerance classes like C5–C3
Ball Screw shaft in production
5. What do the tolerance classes C1, C3, C5, C7 mean?
Tolerance classes indicate how precisely the screw is manufactured — that is, the maximum deviation allowed in positioning:
Class
Maximum deviation over 300 mm
Application
C1
±3 µm
High-precision mechanical engineering, optics, semiconductors
C2
±7 µm
CNC milling, advanced medical technology
C5
±23 µm
Automation, industrial axes
C7
±50 µm
Transport, einfache Positionierung
Class
Maximum deviation over 300 mm
Application
Important: The smaller the tolerance class (e.g., C1), the more precise the product.
6. Difference between T-class and C-class in Ball Screws
In datasheets or catalogs, you’ll often find two different designations for accuracy classes: C-classes and T-classes. Both indicate the manufacturing accuracy of a Ball Screw but follow different standards and purposes. Here’s a brief overview:
6.1 C-classes
These classes come from the ISO standard (ISO 3408) and refer to the manufacturing tolerance of the lead — that is, how precisely the position is achieved over a certain length.
6.2 T-classes
These designations often come from company standards or complement the C-classes — especially in German or European catalogs. They also relate to positioning accuracy but are often used to indicate internal quality levels or additional criteria (e.g., preload, backlash, runout).
- T3 roughly corresponds to C3
- T5 ≈ C5
- T7 ≈ C7
Note: Not every T-class matches a C-class one-to-one — always check the datasheet.
6.3 At a glance
Origin
Meaning
Application
C-Class
ISO-Standard
Measure of lead accuracy in µm
Global technical standard
T-Class
Manufacturer standard
Extended classification including backlash/preload
Supplementary to C-classes, often found in catalogs
Origin
Meaning
Application
If you want to be on the safe side (e.g., for international tenders), the C-class as an ISO standard is more clearly defined. However, the T-class can describe additional quality features that go beyond pure dimensional tolerance.
7. Areas of application with examples
In CNC milling machines or lathes, High-Precision Ball Screws are used to position the tool axes—often with micrometer-level accuracy.
In computed tomography (CT), for example, a Ball Screw precisely moves the tube or the table. Precision is also crucial in laboratory automation and surgical robots.
Here, drives are needed that operate reliably under extreme temperatures—such as positioning units in satellites or actuators in aircraft wings.
In the manufacturing of lenses, lasers, or microscopes, every micrometer counts. High-Precision Ball Screws precisely adjust components—such as in aligning optical paths.
For example, in targeting sensors, remote-controlled platforms, or precise controls in opto-mechanical systems—robust and highly accurate at the same time.
In lithography and processing of semiconductor wafers, highly precise movements are required for exposure, measurement, and handling. Ball Screws ensure consistent quality here.
A single nanometer-scale error can ruin an entire chip. That’s why Ball Screws with tolerance class C1 are used here.
8. Pro and Cons
Cons
✘ Higher price than Standard Ball Screws, especially for ground versions
✘ More sensitive to dirt – requires a clean environment or sealing
✘ Slightly more complex design – for example, due to preload and assembly
Pros
✔ Extremely high accuracy – perfect for positioning tasks in the micrometer range
✔ Very high efficiency (up to 98%) – energy-efficient and low-wear
✔ Long service life thanks to rolling friction instead of sliding friction
✔ Backlash-free design possible – ideal for dynamic systems
✔ Wide range of applications – from mechanical engineering to aerospace
9. Conclusion: When do I need a High-Precision Ball Screw?
When it's not just about “functioning,” but about functioning with high precision—such as for delicate positioning, in safety-critical systems, or with sensitive workpieces. Thanks to different tolerance classes and manufacturing methods, there’s a suitable solution for almost every budget and application.
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.
Want to know more?
Accuracy and Precision
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