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Category: Ball screw

How to measure and select the correct ball screw size?

A Guide to Measuring and Selecting the Correct Ball Screw Size

Introduction:
Ball screws play a crucial role in many automation systems, offering high precision and efficiency in linear motion systems. Choosing the correct ball screw size is essential for ensuring optimal performance and longevity of your machinery. In this article, we will guide you through the process of measuring and selecting the right ball screw size. We will also highlight the brand, STAF, as a trusted provider of high-quality ball screws.

 

  1. Determine the Ball Screw Size: Ball screws come in various sizes and configurations, each designed to meet specific load, speed, and accuracy requirements. Key parameters to consider when measuring and selecting the correct size include the diameter, lead, and nut type.
  • Diameter: The ball screw diameter refers to the size of the screw shaft. Larger diameters offer higher load-carrying capacities. Smaller diameters are suitable for applications with lower loads and where compactness is desired.

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  • Lead: The lead represents the distance the nut travels in one complete revolution. It determines the speed and efficiency of linear motion. Higher leads provide faster travel speeds, while lower leads offer finer resolution and increased precision.

 

  • Nut Type: There are various ball screw nut types available, such as flanged, cylindrical, and compact designs. The nut type should be chosen based on factors like space constraints, mounting requirements, and load capacity.

Image 1: A picture showing how to measure ball screw lead

 

2. Measuring Requirements: To determine the correct ball screw size for your application, consider the following parameters:
  • Load Capacity: Calculate the maximum load that the ball screw will need to support. Consider both static and dynamic loads, as well as any additional forces or moments acting on the system. With this you can select the right ball screw diameter.

Image 2: Ball screw table from STAF catalogue highlighting the basic load ratings columns for Ball screw type FSC.

  • Speed and Acceleration: Evaluate the required travel speed and acceleration for your application. This will help determine the appropriate lead and nut type, as well as the critical speed to avoid resonance issues.

 

  • Accuracy and Backlash: Define the desired level of precision and minimize backlash, which is the play or clearance between the screw and nut. Higher precision applications may require special nut designs or preloading mechanisms. Rolled ball screws are usually of standard precision, C7, while ground ball screws are of higher precision, C5 or C3, C0.

Image 3: [LEFT] Ground Ball screw. [RIGHT] Rolled Ball Screw

Awarding-winning, high quality ball screws from STAF (Taiwan)
When it comes to selecting a reliable ball screw brand, STAF stands out as a trusted provider of high-quality products in Asia. STAF offers a wide range of ball screw options, including precision-ground and rolled ball screws, to meet diverse industrial needs. They are known in Taiwan as the No.1 in linear motion technology.

STAF ball screws incorporate self-developed nanotechnology and stringent quality control processes to ensuring consistent performance and reliability. Their products are designed to deliver long-lasting, smooth and precise linear motion, resulting in improved machine performance and reduced maintenance. In 2023, STAF has just opened a brand new bigger IoT facility in Daxi to cater to the growing demand.

STAF and Shafttech

Due to Shafttech’s large presence in Southeast Asia (SEA), we were awarded SEA distributorship by STAF in 2015. Since then, this partnership has provided comprehensive technical support and application engineering expertise to assist customers in selecting the right ball screw size for their specific requirements. With the support of our customers globally, Singapore and Malaysia has become a hub for STAF in terms of stock inventory. This dedication to customer satisfaction sets STAF apart as a reliable partner in the field of linear motion systems.

Conclusion:

Selecting the correct ball screw size is crucial for achieving optimal performance and longevity in your linear motion system. By understanding the parameters involved, considering load capacity, speed requirements, and precision levels, you can make an informed decision. It is also important to purchase from reputable brands like STAF, which offer high-quality ball screws and expert support. With the right ball screw size, you can ensure smooth, precise, and efficient linear motion in your applications.

(Note: This article is for general applications. It is important to consult manufacturers’ guidelines and technical specifications when selecting ball screws for specific applications.)

If you want to know how to find a suitable replacement for an existing ball screw, check out this video!

Ball screw vs Lead screw: Differences and Benefits

Structural Differences

Ball screws and lead screws are common parts used in linear motion systems. The general function of both is the same – to translate rotary motion to linear motion down a screw shaft. Now let us discuss the differences in their structure.

A ball screw assembly is made up of a screw shaft and a nut that contains ball circuits. These circuits contain steel balls that run along the threads of the shaft and recirculate back into the circuit (refer to GIF below). A lead screw assembly consists of a trapezoidal or acme threaded screw shaft coupled with a lead screw nut. When the nut travels down the lead screw shaft, the internal threading of the nut comes into full contact with the grooves of the shaft. In other words, a lead screw assembly contains no steel balls, unlike ball screws.

   

GIF 1: An illustration of the internal structure of a ball screw nut traveling down a ball screw shaft.

Image 1: An SNB lead screw assembly from Shafttech, consisting of bronze nuts (TMK 25 SNB and TMK 25 OH SNB) on a 2meter long S45C trapezoidal lead screw (TM 25×2000 SNB).

 

What are the benefits of each?

Ball Screw

A ball screw nut is designed in a way to achieve a low friction, smooth and precise linear motion. Therefore, ball screws are used in industrial applications with higher positional accuracy and greater axial loads for robotics, semiconductors, CNC machinery and other contract manufacturing processes. In these applications, ball screws are often used in conjunction with other high precision components like linear guides to form linear actuators, which are in turn used in complex XYZ positioning tables.

Much like a ball bearing, the steel balls within the ball screw nut provide lesser friction as compared to lead screws. This means that lesser torque is required to achieve linear motion. This makes ball screws much more efficient and durable, therefore able to withstand repeated cycles of operation.

 

Lead Screw

A lead screw is generally regarded as a more cost-effective solution to achieve linear motion, but it is mostly used in simple positioning applications that do not require high loads or accuracy.

If you have a vertical application in your system, you may consider lead screw as they have a self-locking mechanism to prevent back drive. But this also means that more external force needs to be applied to power the movement of the nut.

Another advantage is that lead screws are mostly maintenance-free and quieter because there are no steel balls in the nut. However, the higher surface contact between the nut and screw also generates high heat and leads to faster wear and tear.

 

How do you determine which is better suited for your application?

Image 2: Ball screw and lead screw from Shafttech. [Above] A STAF ball screw assembly with end-machining (FSU 2510T4-353-C7-R STAF) and [Below] a SNB lead screw assembly (see image 1).

 

To know this, there are some important factors to consider.

–Precision and accuracy: This is determined by the lead accuracy of the screw assembly. Lead is the distance travel in one full rotation of the nut. Most manufacturing or robotic processes that require precise positioning of their linear movement will opt for ball screws.

–Load: This is also an important consideration factor. Ball screws are able to carry higher axial loads due to their material and higher rigidity.

–Vertical or Horizontal: Vertical applications will favour the use of lead screws as they have a self-locking mechanism and no braking system is required.

–Speed: Ball screws have no issues in high-speed applications and they are also preferred. Lead screws are commonly single-start screws, which means the nut travels slower down the shaft. However, high helix lead screws can achieve high speed linear motion but these screws are more costly and have longer lead times than regular lead screws.

–Noise: Lead screws are quieter in general as the steel balls will generate more vibration in ball screws.

–Maintenance: Ball screws require oil or grease lubrication due to the presence of steel balls but lead screws do not.

–Durability: If your application consists of continuous and high-cycle conditions, ball screw will be recommended as lead screw wears faster due to higher friction and lower efficiency.

 

Indeed, in a complex system, there are other factors involved such as temperature, size limitations, nut housing and mounting requirements. If you are still unsure whether to choose a ball screw or lead screw, you can speak to Shafttech for a recommendation on the type of screw assembly that suits your application. Shafttech specialises in linear motion systems and has been serving automation customers since 2012. We are distributor and supplier of top brands like STAF, Rexroth, IKO, THK, NB, HIWIN, PMI and more. Feel free to contact us at sales@shafttech.com or call us here. Or you could also visit this page for a list of ball screws to select from.