Custom Ball Screw Design

Designing ball screws is sometimes as much art as science. With eyes trained on the new and innovative, while maintaining a healthy respect for what has been proven, our engineers work with the latest design tools to create optimum ball screw and actuator configurations for any application.

A ball screw assembly is primarily an efficient (90% minimum) converter of rotary-to-linear or linear-to-rotary motion. It consists of a screw containing semi-circular form threads, a nut having an internal helical thread of similar form, and a circulating system permitting a continuous flow of steel balls rolling between them.

DESIGN CRITERIA
There are several key design criteria that need to be determined when designing a ball screw to suit a particular application (load, life, speed, backlash,environment, etc). The information provided on this website is a basic overview of this information, and is only intended as a guide to assist you in the selection/design process. Beaver Aerospace & Defense has nearly 60 years of experience in the custom design of ball screws. We can assist you in providing a solution to your specific ball screw needs.

CUSTOM DESIGNS
No standard ball screw can satisfy every application requirement. If you have any questions about the suitability of the current Beaver applications, don’t hesitate to call us. It may be possible to modify one of the Beaver assemblies using other material or finishes for your application. Beaver can work with you to design a custom device for your special requirements. Here are just a few of the unique devices with unusual requirements Beaver has designed and manufactured in the past:

  • Telescopic assemblies with a total retracted length smaller than extended length
  • Restricted envelope designs for mounting limitations and corrosion-resistant assemblies for environments that demand special material and finishes
  • Temperature-resistant designs utilizing special materials of construction and exotic lubricants for temperatures in excess of 300° F
  • Lightweight assemblies for aircraft and aerospace that take advantage of thin wall sections and high structural strength materials
  • Short stroke caged assemblies for limited travel applications that do not require recirculation of bearing balls
  • Special actuator configurations that accommodate gears, splines, and bearings as integral parts
  • Beaver manufactures ball bearing screws as small as 3/16 inch diameter, as large as 24-inch diameter — as short as 1 inch in length, as long as 70 feet in length

Wipers are a standard feature on most ballscrews. Wipers at each end of the ballnut maximize performance by helping to spread lubricant over the screw thread and preventing foreign material from contaminating the ballnut.

  • 90% efficiency minimum – The high efficiency and reliable performance results from the rolling contact of bearing balls riding on an ultra-smooth, precision ground ball groove.
  • Controlled backlash – The axial play in precision ball screws may be reduced to the required need of the application so that a light, smooth operation is still possible.
  • The actual lead of all the standard precision ball bearing screws shown will be accurate within specific inches per foot cumulative, dictated by the application and need.
  • Lubrication – Lube fittings can be provided, if necessary.

Beaver uses the gothic, as well as round ball race profile, as standard designs.

Round Profile

  • Smooth Running
  • Optimal Stiffness
  • Optimal Life
  • Minimum Friction
  • Minimum Wear

Gothic Profile

  • Smooth Running
  • Minimum Friction
  • Minimum Wear
  • Negligible Axial Play

An overrun/dog stop can be provided to prevent damage by accidental overrun at either end.

Such a stop should be considered a secondary method only. The travel should be stopped by the control system of the assembly itself.

Beaver ball bearing screws are more than 90% efficient when rotary input is converted to linear translation. Because of this feature, it is possible to “back-drive” the unit by applying axial force to either the ball bearing nut or screw when the other member is not restrained from rotation.

When a ball bearing screw is used in this fashion, Beaver should be consulted for the expected efficiency. It varies with the helix angle of the ball thread. In such cases, it is desirable that the lead should equal the ball circle diameter or be no smaller than one half the ball circle diameter. Because of this high efficiency, applications which require holding the load (such as a jacking device) require a locking method in the drive. This could be a brake, irreversible gearing or sprag clutch and friction pad.

Ideally, ball screws should be fully enclosed, in which case wipers may not be required. Should the design not permit such enclosures, standard Teflon (PTFE) wipers are available. For special conditions, other materials such as elastomer, plastic, carboxylated  polyurethane, felt, self lubricating composite material, etc., may be used. In such instances, please contact Beaver for advice. Beaver ball bearing screws incorporate positive seals to exclude fine particles of foreign matter and retain lubricant in the ball bearing nut.

A ball return system is necessary to ensure the continuous circulation of the balls. Beaver uses two predominantly different systems:
INTERNAL BALL RETURN AND
EXTERNAL BALL RETURN

Two types of holding methods that are effective in keeping a ball screw from back driving are spring-set electrically-released brake ERS and Bidirectional no-back clutches.