Understanding the different types of ball screws

A ball screw is a high-efficiency method of converting rotary motion to linear motion. It’s able to do this by using a recirculating ball mechanism between the screw shaft and the nut. There are many different types of ball screw, each with their own uses and advantages. Continue reading to understand the different types of ball screws, including the precision ground ball screw and rolled ball screw.

What is a ball screw?

Converting rotary motion into linear motion, ball screws (which were originally called antifriction nuts) feature a long threaded shaft with ball bearings that are able to withstand significant weight and stress. They achieve this while minimising friction.

A ball screw has both a screw and a nut. It also has helical indentions formed on the outside of both, which allows ball bearings to roll between them. During the ball screw rotation, the ball bearing travels to the return system before changing direction.

Ball screws are used in a wide array of manufacturing applications, including automobiles, 3D printers and aeroplanes.

Different types of ball screws

There are a wide variety of applications and uses for ball screws, with two main types chosen by manufacturers:

• Rolled ball screw
• Precision ground ball screw

Difference between rolled ball screw and precision ground ball screw

The first difference between rolled ball screws and precision ground ball screws is their fabrication process. Ground ball screws are created through an abrasion process, in which an abrasive cutter moves along the length of the horizontally positioned blank, carving out threads of the screw.

Rolled ball screws are manufactured using rotating tool dies in which the blank is pushed back and forth between the dies. This helps to shape the threads in the screw, and is popular because of its high efficiency.

When comparing cost, there is a considerable difference between rolled ball screws and precision ground screws. Because of their efficiency, rolled ball screws are usually more cost-effective than ground screws. However, ground screws are often preferred for machinery that requires high precision because they offer more accuracy than rolled screws.

When it comes to comparing accuracy, ground ball screws are superior to rolled ball screws because the threads are crafted more precisely and smoothly than its counterpart. When a screw is more accurate, the nut moves smoothly along the shaft.

Pros and cons of ball screws

There are two main benefits of using ball screws: efficiency and low friction. A ball screw offers a high level of mechanical efficiency. Statistics show that they can deliver up to 90% efficiency compared to lead screws, which offer an efficiency of between 20% and 25%.

Ball screws also produce minimal friction, which is ideal for producing a smooth application. They’re designed with a nut in which ball bearings circulate and create a smooth gliding surface for the screw. This reduces friction and increases the ball screw’s lifespan.

There are other benefits to using ball screws too, which are:

• Higher accuracy grades for greater positional accuracy
• Available in rolled and ground types
• Can be adjusted to increase/decrease preload
• Need to be replaced less frequently
• Available in screw diameters from 4mm to 80mm

In terms of the negatives of ball screws, there are only really two: their susceptibility to be back-driven and their cost.

Since ball screws create such low friction, they can be back-driven at certain lead angles.

Ball screws can also be slightly more expensive than other options. They tend to cost slightly more than similar mechanical devices, including lead screws. So for manufacturing companies on tighter budgets, the higher cost may be a deterrent.

However, because of their clear advantages of superior mechanical efficiency and low internal friction, ball screws are still a very popular choice for many manufacturers and are a wise investment.

Ball screws at Matara

At Matara, we are a leading rolled ball screw manufacturer and offer a range of linear ball screws in both ground and rolled options. We stock a wide range of ball screws and end supports from TBI Motion. Of all the types of screws used for motion within the industry, linear ball screws provide unique benefits compared to other solutions.

We also provide a range of end supports in both fixed side and floated side formats, as well as ball screw housing units.

If you would like to know more about the ranges of rolled ball screws and precision ground ball screws available from Matara, take a look at our product pages or contact one of our team on 01684 850 000.