Miniature Ball Screw 0802 for Drilling Machine

Miniature Ball Screw 0802 for Drilling Machine The ball screw is a screw transmission element between the screw and the nut with a steel ball as a rolling body.It can change rotational motion into linear motion,or linear motion into rotational motion.Therefore, the ball screw is not only the transmission element,but also the reciprocal transformation element of linear motion and rotational motion.

1.Lead and Pitch

Lead and spacing are a good example of related but different specifications.The Lead refers to the linear distance traveled for each complete turn of the screw,while the pitch is the distance between the screw threads.These terms are often used interchangeably,and for single-start screws(as defined below),lead and pitch are equivalent.However,for screws with multiple starts,the lead and pitch are not equal.

2.Circuits and Turns

Also related is the concept of ball circuits and turns.A ball circuit is a closed path of recirculating balls."Turns"refers to the number of trips the ball can make around the screw shaft before recirculating.The relationship between the Circuits and the turns is affected by the recirculation method.The return cue uses either a deflector or a threaded to threaded(also known as a cross)method to recirculate each turn of the ball individually.So the number of turns is equal to the number of circuits.

Internal Deflector Recirculation

Recirculating balls can pass through multiple threads as the ball returns through an internal channel or an external tube,so a Circuit can have multiple ball turns.In other words,the ball bearings go several times around the screw shaft before recirculating.Multi-start ball screw assemblies usually use the inner channel recirculation method.The nut body can be designed to have multiple Circuits by incorporating multiple internal recirculation channels into it.

Internal End Cap Recirculation

External Tube Recirculation

3.Starts(and Lead revisited)

Return to the lead for a minute.This is not only an important specification for linear travel and speed,but also because the lead of the ball screw determines how many balls are in the load zone(in contact with the screw shaft and ball nut)and therefore has a direct impact on the load capacity.

Given the geometry of the screw assembly,it makes sense that as the screw lead gets larger,the number of rails inside the ball nut gets smaller,and so there are fewer balls to carry the load. Although larger Lead Screws provide longer travel per turn and higher speeds,their ability to deliver high load capacity is compromised.In theory,it is possible to increase the number of ball tracks by extending the ball nuts,but manufacturing constraints and limitations on the length of the ball nuts make this an impractical solution.

To solve the problem of fewer turns in long lead assemblies,Ball Screws and nuts can be manufactured with multiple "starter" or ball tracks.This puts more ball bearings into the load bearing area and increases the load capacity.

Single and Double start screw

Multiple ball screw has safety advantages over single starting screw.If one ball track is damaged or tired,balls in other tracks can help prevent catastrophic failure.Furthermore,when a single-starting ball nut is used with a multi-starting screw shaft,the assembly can be refurbished by replacing only the ball nut and not the screw shaft.The new ball nuts are mounted on existing screws in unused rails,saving cost and avoiding the need to completely remove the screw system.

While this may seem like a semantic exercise,understanding these terms and the differences between them can help designers and engineers avoid incorrect assumptions about ball screw operation and performance.