Ball Screw Design Resources

Lead Error Standards  Determining Ball Screw Load
Ball Screw Cause/Effect Considerations Determining Critical Speed
Determining Ball Screw Life  

 

 

 

 

 


Lead Error Standards

Lead error refers to the error in lead length per turn, compared to the basic lead specified.  We manufacture ground ball screws up to ANSI Class 2 or DIN/JIS Class 1 specification.

ANSI C2, DIN/JIS C1

0.0002 in/ft or 5 μm/300mm

ANSI C5, DIN C3

0.0005 in/ft or 12 μm/300m

ANSI C7, DIN C5

0.001 in/ft or 25 μm/300mm

ANSI C8

0.006 in/ft or 150 μm/300mm


Determining Ball Screw Load

The amount of load to be moved is used to select the proper screw size.

 

Vertical load move: The nut load is equal to the weight to be moved plus the friction load.
 

Horizontal load move: The nut load is determined by multiplying the weight by the coefficient of friction.
 

Loads can also be measured with a spring scale or dynamometer, which is recommended for loads that are neither vertical or horizontal. The higher the load, the larger the size of the screw and nut is needed. The load capacity of a ball screw can be increased by increasing screw diameter, nut length, quantity of internal balls or ball diameter.


Ball Screw Cause/Effect Considerations

The following chart indicates the relationship between various design specifications and operation parameters.

 

INCREASE IN:

AFFECTS:

HOW:

Screw Length

Critical Speed

Decreases

Column Load

Decreases

Screw Diameter

Critical Speed

Increases

Inertia

Increases

Stiffness

Increases

Load Capacity

Increases

Column Load

Increases

Lead

Torque

Increases

Load Capacity

Decreases

Positioning Accuracy

Decreases

Angular Velocity

Decreases

Angular Velocity

Critical Speed

Decreases

Mounting Rigidity

Critical Speed

Increases

System Stiffness

Increases

Load

Life

Decreases

Nut Length

Load Capacity

Increases

Stiffness

Increases

No. of Balls

System Stiffness

Increases

Load Capacity

Increases

Preload

Positioning Accuracy

Increases

System Stiffness

Increases

Drag-Torque

Increases

Ball Diameter

Life

Increases

Stiffness

Increases

Load Capacity

Increases

Lead

Increases

 

Determining Critical Speed

Critical speed is the angular velocity at which the screw (or nut) develops severe vibrations.  Regardless of mounting orientation, a ball screw assembly must operate below its critical speed to avoid vibration, noise and possible failure. The magnitude and location of the shaft unbalance, the length of the shaft, shaft diameter, and the type of bearing support are factors which affect critical speed.


Determining Ball Screw Life

The useful life of a ball screw assembly, usually given in terms of one million inches of travel. The operational load rating is a major determinate of ball screw life.  Every application is unique; duty cycle and environment also have an effect.  Customers are encouraged to consult with our engineering staff to discuss the specific requirements of their applications.

Precision Ground Ball Screw

Custom manufactured for new OEM designs and replacement applications

Learn More

Form is being submitted, please stand by...