Rockford Ball Screw Co.
Contact: Dave Beck
3450 Pyramid Drive
Rockford, IL 61109
U.S.
Phone: 800 475 9532
Fax: 815 84 7897
Rockford Ball Screw Company began its life in 1973. For the last 30 years we have achieved a tremendous growth rate. We have realized this growth accomplishment by providing high quality products, extensive engineering expertise, extremely competitive pricing, industry leading on-time delivery performance, and outstanding customer service. Our product line consists of 55 standard models, many of which are inter-changeable with other rolled thread manufacturers. Rockford Ball Screw has developed a solid foundation with the best-qualified people, state-of-the-art equipment, and an excellent manufacturing facility.
We are a manufacturer of Rolled Ball Screw Assemblies, Acme Screws and Nuts, Ball Screw Bearing Supports. We offer full capability machining to modify custom applications. We have many years of experience in retrofitting ball screws into applications that did not previously use ball screws. We also manufacture replacement kits for Bridgeport © Knee Mills and other "clone" mills.
RBS recently achieved ISO 9001:2000 Certification recognizing that the company's quality system meets standards developed by the International Organization for Standardization. Implementing a quality management system based on the ISO 9001:2000 standards was a logical step for our company and demonstrates our commitment to continuous improvement and our resolve to achieve total customer satisfaction
Please visit our web site for downloadable PDF files, product updates, and additional information not listed in the catalog.
Note: The products shown in this catalog are intended for industrial use only and should not be used to lift, support or otherwise transport people, unless you obtain a written authorization for each individual application form Rockford Ball Screw Co. The specifications and data in this publication are believed to be accurate and reliable. However, it is the responsibility of the product user to determine the suitability of Rockford Ball Screw products for a specific application.
A ball screw is just that: a screw which runs on balls. The screw and nut have matching helical grooves or races, and the ball bearings recirculate in these races. There is no physical contact between the screw and the nut. As the screw or nut rotates, and the rolling balls reach the trailing end of the nut, they are deflected or guided from this "pitch" contact by means of a return tube and returned to the leading end of the circuit. There, the cycle resumes and the balls recirculate continuously.
The ball screw is a simple device for transmitting power mechanically. It is an efficient converter of rotary-to-linear or linear-to-rotary motion. It is a member of the family of power transmission screws. However, it possesses many more important sales and engineering advantages than conventional screws as well as other means of power transmission.
Mechanical Efficiency
Is in excess of 90% of input. High efficiency permits use of smaller power sources resulting in savings of space and money.
Predictable Life
When given the operating conditions, ball bearing screw life is predictable within 90% of the time. The load life relationship is determined in the same manner as the bearing industry rates ball bearings. The B10 life means that 10% of the units could fail before reaching the required travel (at rated load) and that 50% of the units will exceed five times the rated travel. This relationship is based on the inverse cube ratio. meaning that if a unit operates at 1/2 the rated load, the life of the unit increases eight times. All load ratings are in accordance with ANSI B5.48-1977.
Precise Positioning
Rolled thread ball screws can be designed with proper controls to give extreme repeatable accuracy throughout the life of the screw.
Maintenance Free
Virtually the only requirement is to lubricate periodically; a minimum of light oil or a fine grease for optimum operation.
No Stick Slip
Uniform feed rate or smoothness of travel results from the principle of rolling contact versus sliding metal-to-metal contact. This rolling contact eliminates the tendency to stop-start or stutter. In machine tool slide applications, this can result in a tremendous increases in "tool life".
Reliability
Extreme reliability is achieved under various operating conditions.
Note: The products shown in this catalog are intended for industrial use only and should not be used to lift, support or otherwise transport people, unless you obtain a written authorization for each individual application form Rockford Ball Screw Co. The specifications and data in this publication are believed to be accurate and reliable. However, it is the responsibility of the product user to determine the suitability of Rockford Ball Screw products for a specific application.
Ball Screw Selection
There are as many different types of ball screws as there are applications. A clear understanding of what you want to accomplish will help guide you to the right one. Here's a list of questions to help you decide which ball screw is best for your application:
1. What is the load?
2. How fast does it need to move?
3. What is the overall length between bearings?
4. How will it be mounted: Horizontally or vertically?
5. Will you have bearing supports at one or both ends? What kind of bearings will be used? Fixed or simple or one of each?
6. Stroke length: How far does it need to move?
7. How many cycles/hr? How many hours per day? How many days per year? How many total years do you want it to operate?
8. How accurate do you need the operation? What is the linear accuracy in inches/foot required?
9. Is there any external force that will be exerted on the ball screw? Are all forces axial?
10. What is the maximum backlash permitted? If zero, a preloaded ball nut assembly is required.
11. Cycle time: How long do you want it to sit before retracting?
12. What type of lubrication are you using?
How to Order a Ball Screw
1. Select and specify model number from this site.
2. Specify overall length of screw stock (threaded length plus any machined lengths).
3. If screw is to be machined at factory: [A] With standard ends(s) refer to it by the corresponding letter designation mentioned in Standard End Machining. [B] With end(s) machined by us to your specifications, please submit a sketch or drawing showing all dimensions and the direction you want the mounting flange or ball nut thread to face when mounted on your screw.
4. If screw is to be machined at your facility, specify if you want the screw shipped to you cut-to-length and hard, or cut-to-length and annealed by our induction annealing equipment. Specify the length each end should be annealed.
5. Specify if screw lead accuracy required is standard grade or lead accuracy stock. If you are running two or more screws in tandem, please specify "MATCHED LEADS" for each set of screws ordered.
6. To order the ball nut, determine if the axial backlash in our standard ball nuts is sufficient. Specify "OVER-SIZE BALLS" to reduce backlash. If NO axial backlash is desired, specify that a PRELOADED ball nut assembly is required.
[If you are submitting a drawing please indicate which direction you require the mounting thread or flange of the ball nut to face on the screw. Also specify if you want the ball nut mounted on the screw or shipped on a mandrel.]
7. Specify if a standard mounting flange is required. If so, is flange supplied to be mounted or loose? If relationship of return tube area to mounting holes is critical, specify this relationship.
8. If a special flange is required, submit a drawing or sketch.
9. Specify if wipers are needed. If so, refer to Flange & Wipers for various mounting configurations.
10. To order other component parts such as safety springs and repair kits, consult factory.
Technical Data
MAJOR DIAMETER: The outside diameter of the ball screw.
MINOR DIAMETER: The root diameter of the ball screw thread.
LEAD: The linear distance the ball nut or screw will travel in one revolution.
LEAD ACCURACY: The maximum variation of lead measured in inches per foot. The standard grade of accuracy is .007" per foot cumulative. The premium grade is .003" per foot cumulative. Ref. Class 7-8 ANSI B5.48-1977. Lead charts are available upon request.
BACKLASH (AXIAL LASH): The axial free movement between the ball nut and ball screw. It determines the amount of lost motion between the ball nut and screw on a horizontal application. Backlash on standard nuts range from .004 to .018, depending on size of screw.
SELECTIVE FIT: Standard ball nuts can be custom fitted with oversize balls to reduce backlash to .003 inches.
PRELOAD: The use of two groups of ball bearings, loaded in opposite directions to eliminate backlash in a ball screw assembly. Preloading increases screw screw stiffness and provides for accurate positioning with very little increase in applied torque.
SCREW STRAIGHTNESS: Standard straightness is .010" per foot TIR, not to exceed .025" TIR over the entire length of the screw.
EFFICIENCY: The ratio of work output divided by work input. Generally this is >90% for ball screws.
STROKE: The linear distance in either direction that a ball screw or ball nut travels in moving the load.
CYCLE: A complete forward and return stroke.
THRUST LOAD: A load parallel to and concentric with the center line of the ball screw, which acts continuously in the same direction. Thrust loading is the recommended method of attaching the load to the ball screw.
COMPRESSION (COLUMN) LOAD: A load that tends to buckle or compress the screw shaft.
TENSION LOAD: A load that tends to stretch the screw shaft. A greater selection of screw sizes are available when tension loading is present because there are no column load limitations.
OFF-CENTER LOAD: A load that puts a moment load on the ball nut. This type of loading will reduce ball screw life.
SIDE-LOAD: A load that is applied perpendicular to the screw shaft. This type will also reduce the life of a ball screw assembly.
DYNAMIC LOAD (OPERATING) RATING: The maximum thrust load under which a ball screw assembly will achieve a minimum of 1,000,000 inches of travel life.
STATIC LOAD: The maximum load (including shock loads) that can be applied to a stationary ball screw assembly before there is permanent deformation of the ball rack in the ball nut or screw.
BALL SCREW LIFE (LIFE EXPECTANCY): Is expressed as total revolutions or inches of travel an assembly will operate under a rated load in a clean environment with proper lubrication. About 90% of all ball screws operated at rated loads will meet or exceed a million inches of life before evidence of fatigue appears. Although 10% may not each a million inches, 50% could exceed 5 million inches.
TEMPERATURE: Ball screws operate with normal efficiency between temperatures of -65°F to 300°F with suitable lubricants.
LUBRICATION: Ball screws should not be operated without proper lubrication. Consult service manual for recommendations.
FINISH ON BALL SCREW ASSEMBLE: Ball screw assemblies are supplied with Black Oxide-type finish. Other finishes are available per customer specifications.
BRUSH WIPERS: Brush wipers help to prohibit contaminates from entering the ball screw assemble. Brush wipers are recommended for any application where contaminates might be deposited on the ball screw.
MATERIAL/HARDNESS: Most screws and nuts are made of alloy steel. They are hardened to RC 56 minimum. Stainless screw models generally are made of 17-4PH material. This stainless steel is normally precipitation hardened to RC 40 minimum.
MACHINED-END CONFIGURATIONS: Rockford Ball Screws can be furnished with or without end journals. Standard type journals to accommodate single bearings, duplexed bearings, multiple sets of duplexed bearings or pillow blocks are available upon request. Screws can also be machined to customer specifications if drawing is submitted. If customer wants to do the machining, screw can be furnished hard or annealed each end to specified lengths.
RETROFITING BALL SCREWS: Rockford Ball Screw has many years of experience in adapting and retrofitting ball screws into applications that don't currently utilize ball screws. We offer engineering assistance as well as ball screw repair services.
COLUMN STRENGTH: The maximum compressive load that can be applied to a ball screw assembly without resulting in failure due to elastic instability. Column strength is a function of the ball screw diameter, supported length of screw and the rigidity of the bearing supports.
CRITICAL SPEED: The maximum speed at which a ball screw or ball nut can rotate without producing destructive resonant vibrations. The critical speed is a function of the ball screw diameter, the unsupported length of screw, rigidity of bearing supports and RPM.
BACKDRIVING: This is the ability of the screw to reverse by applying a thrust load to the ball nut to drive the screw and develop torque, or applying a thrust load to the screw to drive the ball nut. The higher the relationship of the lead of the screw to its diameter, the less effort is required to obtain a smooth, positive backdriving effect. The lead of the screw should ideally be equal to the diameter of the screw. Any screw with a lead less than one third of its diameter is not recommended on a backdriving application.
SYNCHRONOUS SCREWS: Screw synchronization is achieved by selecting screws with closely-matched lead errors. These screws can be driven in tandem by a single motor source to eliminate binding. To order synchronous screws ask for "MATCHED LEAD SETS" when ordering.
SAFETY SPRINGS: The safety spring is a coil spring installed in the inactive part of the ball nut. In the event the ball bearings are lost from the nut, the safety spring will assume the load and prevent the ball nut from "free falling" down the screw. Safety springs need to be specified when ordering.
TORQUE FORMULAS: The amount of torque to move the load is measured in inch-pounds. The formulas are:
ROTARY TO LINEAR (DRIVE TORQUE)
Torque = .177 x Load x Lead of Screw
LINEAR TO ROTARY (Backdriving Torque)
Torque = .143 x Load x Lead of Screw
PRELOAD TORQUE (Additional torque Due to Preload Only)
Preload Torque = .034 x Preload Setting (lbs. ) x Lead of Screw
TORQUE - H.P.
Torque = 63,000 x HP
RPM (speed)
ANGULAR VELOCITY FORMULA
RPM = Velocity (inches/min.)
Lead (inches/rev.)
