Ballscrew

A ballscrew, also known as a ballscrew or ball bearing screw, is a mechanical component used to convert rotational motion into linear motion. It consists of a threaded shaft (screw) and a nut that contains a series of recirculating ball bearings. The screw is typically made with a helical groove, and the nut has corresponding internal grooves that match the screw’s thread.

The ball bearings in the nut allow the screw to move smoothly and efficiently, with minimal friction. As the screw rotates, the ball bearings recirculate within the nut, causing linear motion along the axis of the screw. This mechanism provides high precision and reduced backlash compared to other types of screws.

ballscrew

Ballscrews are commonly used in various industrial applications where precise positioning and high load capacity are required, such as CNC machines, industrial robots, aircraft controls, and automotive steering systems. They offer advantages such as high efficiency, low wear, and long service life. The performance of a ballscrew can be influenced by factors such as lead (the distance traveled by the nut per revolution of the screw), pitch (the distance between adjacent threads), and the quality of the ball bearings used.

linear axis drive that uses a ball screw

Components of the Ballscrew

The main components of ball screws are the screw shaft, the nut, and the ball bearings (or balls).

Components of the Ball Screw
Components of the Ball Screw

Specifications of the Screw Shaft:

Nominal Diameter
The nominal diameter is the maximum diameter of the screw shaft excluding the ball bearings.
Ball Circle Diameter
Ball circle diameter (or pitch circle diameter) is the center-to-center distance of two opposite balls measured when the ball bearings are in contact with the grooves.
Root Diameter
Root diameter is the distance between the bottommost section of the groove to the bottommost section of the opposite groove. It is the minimum diameter of the screw shaft.
The nominal diameter, ball circle diameter, and root diameter are used in calculating the application characteristics and in sizing the screw.
Pitch
Pitch is the axial distance between two adjacent threads.
Lead
Lead is the linear distance along the axis of the screw that is covered by one complete rotation (360°) of the screw. It is an important specification of a ball screw which determines linear travel and speed and load capacity. As the lead of ball screws increases, the linear distance covered and the speed increase. However, the number of balls accommodated around the screw shaft decreases, resulting also in a decrease in load capacity.

Specifications of the Screw Shaft
Specifications of the Screw Shaft

how to size a ballscrew

ball screw with guide bearing and nut holder
ball screw with guide bearing and nut holder

To size a ball screw you :

  1. Determine the load. This is the most important factor in sizing a ball screw. The load includes the static load, which is the weight of the moving parts, and the dynamic load, which is the force applied to the moving parts during operation.
  2. Calculate the pitch. The pitch is the distance between the threads on the ball screw. The pitch is inversely proportional to the lead, which is the distance the screw moves for each turn of the nut.
  3. Select the diameter. The diameter of the ball screw is determined by the load and the stiffness requirements. A larger diameter will provide more stiffness, but it will also be heavier and more expensive.
  4. Select the length. The length of the ball screw is determined by the travel distance required.

Once you have determined all of these factors, you can use a ball screw sizing chart to find the correct ball screw for your application.

Here are some additional tips for choosing the ball screw for your application::

  • Oversizing is better than undersizing. If you are not sure what size ball screw to use, it is better to oversize than to undersize. An undersized ball screw will not be able to handle the load, and it may also be damaged.
  • Consider the environment. If the ball screw will be used in a harsh environment, such as a dirty or dusty environment, you will need to select a ball screw that is designed for that environment.
  • Consider the future. If you think that the load or the speed requirements of your application may change in the future, you should select a ball screw that is capable of handling the increased load or speed.

Leave a Reply