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Lead Screw
 

Lead screw overview

Lead screw is a linkage in machine used to convert rotatory or turning motion in to linear motion. Lead screw consist of threaded rod with a nut.However lead screw threads are optimized to reduce friction. Lead screws gerally have shorter lead length to provide precise positioning. Lead screws have large frictional energy losses compared to other options due to thier large area sliding contact between nut and screws.

Lead screw types

  • Square thread

    Square threads are made up square shape teeths. This kind of threads have least friction hence are most effcient. This type of lead screws are used in high power applications. This type of lead screws are expensive as difficult to manufacture.

  • Acme thread

    Acme threads have a 29° thread angle, which is easier to machine than square threads. They are not as efficient as square threads, due to the increased friction induced by the thread angle. Acme threads are generally also stronger than square threads due to their trapezoidal thread profile, which provides greater load-bearing capabilities.

  • Buttress thread

    Buttress threads are of a triangular shape. These are used where the load force on the screw is only applied in one direction.They are as efficient as square threads in these applications, but are easier to manufacture.

Lead screw advantages

  • Large load carrying capability
  • Compact
  • Simple to design
  • Easy to manufacture; no specialized machinery is required
  • Precise and accurate linear motion
  • Smooth, quiet, and low maintenance
  • Most are self-locking

Lead screw disadvantages

  • Not very efficient. Due to the low efficiency they cannot be used in continuous power transmission applications.
  • high degree of friction on the threads, which can wear the threads out quickly
  • Low duty cycle as friction genrates more heat

Lead screw Applications

  • Machine tools
  • aero space
  • automatic gates.

Difference between lead screw and ball screw

  • Lead screw thread profile is generally trapezoidal, ball screw threads are more rounded.
  • Lead screw nut mate directly with screw where as ball screw nut do not directly mate with screw.
  • Lead screw has a long path of sliding friction between the nut and the screw, ball screws experience only rolling friction between nut and screw.
  • As for accuracy, ball screws generally have the edge over lead screws thanks to reduced backlash.
  • Lead screws cost less , Ball screws cost more
  • Lead screws require more powerfull motor to move the same load compare to ball screw.
  • Lead screws are self locking , Ball screws needs brake.