High-Precision Ball Screws

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.

Learn what efficiency (%) is and how it’s calculated here

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:

1. have very tight manufacturing tolerances
2. are often backlash-free (preloaded)
3. are finely ground or whirled
4. operate reliably with micrometer-level accuracy

In short: High-Precision Ball Screws are the “precision tools” among Ball 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:

1. Function A: Rotation of the screw → linear movement of the nut
2. 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:

1. Series production with moderate requirements
2. Applications where some backlash is acceptable
3. 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:

1. CNC machines, precision axes
2. Positioning drives in medical technology
3. 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:

1. Applications with higher demands
2. Good surface quality and tight tolerances
3. Tolerance classes like C5–C3

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:

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).

1. T3 roughly corresponds to C3
2. T5 ≈ C5
3. T7 ≈ C7

Note: Not every T-class matches a C-class one-to-one — always check the datasheet.

6.3 At a glance

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

8. Pro and Cons

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.