What is a high helix ball screw?

Ball screws and lead screws are specified by the diameter of the lead screw shaft and the lead(or pitch in some cases)of the lead screw.Lead specifies the distance the nut travels on each turn of the screw,produced by a thread or helix wraps around the shaft of the screw.If the screw is"unwrapped"from the screw,it can be used with the circumference of the screw and the lead to form a right triangle.The helix serves as the hypotenuse of the triangle,and the circumference and lead form the other two sides.In this triangle,the angle formed by the circumference of the screw and the helix is called the lead angle(B);the angle formed by the lead and the helix is called the helix angle(A);the lead and spiral angles are complementary(their sum must equal 90 degrees),so if the lead Angle is larger,the spiral angle will be smaller.

Angle A(formed by the helix and the lead)is the helix angle.Angle B(formed by the helix and the circumference of the screw)is the lead angle.These angles are complementary,so if one gets bigger,the other has to get smaller.

Note that some references refer to the angle(B)between the circumference of the screw and the helix as the helix angle.When using the term"spiral angle,"be sure to look for definitions or diagrams to confirm the angle being referenced.High-pitch screws are generally considered to have a lead(P)equal to or greater than the screw diameter(d0).

The lead of a large screw is at most 6 times the diameter of the screw.

Examples of high helix screws include sizes 20x20,6x25,and 40x80,with some large screw designs having wires up to six times the diameter of the screw.And the bigger the lead,the faster the linear travel.As a result,the large screw maximizes linear travel speed while keeping the diameter,mass and inertia of the screw small.By keeping the rotational speed low,audible noise and vibration are reduced.

Because of the large lead of the high screw,that is the screw wrapped around the screw is"stretched",there is less contact between the effective ball(in the case of the ball screw)or the screw nut supporting the load(in the case of the screw).To combat this,some manufacturers add additional ball rails or turns to the screw shaft-a design often referred to as multi-start screws.For ball screws,increasing the number of turns or tracks increases the number of balls available to carry the load.For the lead screw,increasing the number of turns increases the contact area available to carry the load,but also increases friction and heat,which affects the PV value of the screw.

The opposite of a high pitch or high lead screw is a fine pitch or fine guide screw.Fine pitch screws are usually defined as screws with wires less than half the diameter of the screw,such as 16x5 or 12x2 sizes.Fine pitch screws are usually used where very small movements are required.

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