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Introduction to Lead Screws

What Are Leadscrews Used For?

Leadscrews, also often written as Lead Screws, are remarkably common components, and can be found in engineering environments operating lathes, CNC machines or complex robotics. However they can just as commonly be found around the home, in conventional products such as printers or DVD drives. 

A Leadscrew’s main purpose is to rotate, using its thread to push a Leadscrew Nut forwards and backwards in small, very precise increments. By rotating with a Nut attached, a Leadscrew converts rotary motion into linear motion, making it a type of mechanical linear actuator. This is why Leadscrews are often known as a power screw or a translation screw. 

What Do Leads And Starts Refer To?

The ‘lead’ of a Leadscrew is the distance which a Leadscrew Nut will move during one 360° rotation of the screw. This is not to be confused with Pitch, which refers to the distance between the crests of the screw thread. A smaller Lead results in a tighter thread, which allows for more precise movements per rotation.

The ‘starts’ of a Leadscrew are the number of independent threads or ‘teeth’ on the screw itself. A larger number of starts results in a more robust mechanism with a greater ability to transmit torque, but multiple starts can sometimes be incompatible with a small Lead due to space limitations.

For single start Leadscrews, the Pitch and Lead of the screw are equivalent to one another. However for Leadscrews with multiple starts, which are commonly used for applications requiring higher load capacities and higher operating speeds, the Lead is the number of starts multiplied by the Pitch.

Advantages Of Using Leadscrews

The most obvious advantages of using Leadscrews over Threaded Rods include:

  • Large load carrying capacity
  • Smooth and quiet operation
  • Highly accurate and precise linear motion
  • Self-Locking capability (in vertical applications)

Leadscrews are becoming increasingly useful in markets requiring very intricate movements and ultra-high precision actuation. These include non-flight critical aircraft actuation systems, high precision robotics and animatronic limbs and also in medical equipment such as centrifuges and automated pipetting systems.

One of the most common applications of Leadscrews is for positioning the print head in 3D printers. They often use 8mm Leadscrews as demonstrated in the video below. The concepts explained above are all shown in the first few seconds of this video: