Kuroda Jena Tec : Principles of Ballscrew Repair

Kuroda Jena Tec's ball screw repair technicians can recondition or repair ballscrews of any make or configuration with a range of transfer systems. At our specialised repair and testing facilities, we can recondition ballscrews up to 15m in length and 200mm in diameter. Additionally, we can replace ballscrews, offering a re-engineered matched replacement utilizing our existing inventory, up to 80mm in diameter.

Every repair evaluation includes a health check and free of charge assessment report. Our skilled technicians will disassemble, clean, inspect and determine cause of failure. The ballscrew is initially inspected for shaft straightness, bearing journal total indicated runout (TIR), fine thread and journal condition and wear to the shaft.

The ballscrew is then stripped and all parts are vapour de-greased and checked internally for Ball transfer system damage, Brinelling, fatigue, corrosion and damage to raceways. Each individual ballscrew shaft raceway is then polished, fine threads are cleaned and dressed out if necessary. The ballscrew is reassembled using new, high quality chrome steel balls to the correct pre-load specification. Lastly, the ballscrew is put through a series of tests and one final inspection to ensure precision and quality. If it is predetermined that the ballscrew is beyond economical repair, Kuroda Jena Tec offers reverse engineering and will quote for a replacement ballscrew manufactured in accordance with the sample. This should also be considered if the ballscrew is in a poor but running condition. Ballscrew sizes in diameter up to 80mm and in precision grade are held in stock in the UK and USA which can be retrofitted for replacements. Sizes over this diameter are supplied through Kuroda Jena Tec's German facility supported by the regional technical office. Warranties offered on repair services are dependent on repair assessment, ranging from zero warranty (where a replacement is recommended) to 6 months maximum. For more details on how Kuroda Jena Tec can supply your requirements please visit our websites on www.jena-tec.com www.jena-tec.co.uk www.jena-tec.de

Principles of Ballscrew Repair

Principles of Ballscrew Repair

What exactly does happen to a ballscrew when it fails and what are the principles and procedures to repair a ballscrew from a company such as Jena Tec?

The most frequent cause of failure of a ballscrew is either loss of pre-load or rough running typically characterised by a fault flagged by a CNC control system of a machine tool or dimensional inaccuracy or poor surface finish. This in turn is caused by gradual degradation of the ballscrew surface through metal to metal contact of the re-circulating balls to the hardended metal surface of the ballscrew shaft. This repeated contact over an extended period of time leads to a worsening of the ballscrew surface and ultimately erosion and wear.

Lubrication can therefore have an obvious impact on the lifetime of the ballscrew as well as protection from debris from the machining processes. Over time as a machine condition worsens, axis covers and bellows can be damaged and allow machining debris to enter the ballscrew nut even through wiper seals. Over lubrication can also be problematic particularly with grease lubricated systems where too much lubrication can cause pressure on the ballnut return system causing the tube to literally burst with excess grease.

The second most frequent cause of ballscrew failure is catastrophic failure due to an exceptional shock load, which is more commonly recognised as a machine crash. The abrupt excessive load and rapid decceleration from a machine crash can cause buckling of the ballscrew shaft and damage to the ballnut itself including splitting some of the re-circulating balls within the ballnut meaning even if the machine runs afterwards the ballscrew will very quickly fail after a short period of running.



Typical Ballscrew Failure Points

A - Metal Fatigue & Wear to Bearing Surfaces
B - Surface Brinelling
C - Wear & Damage to Balltrack
D - Loss of Squareness to PCD
E - Ball Wear/Breakage
F - Loss of Pre-Load
G - Shaft Bent
H - Damaged Threads
I - Uneven wear over Balltrack
J - Poor System Concentricity
K - Wiper Seals Worn Leaking Lubricant
L - Excessive Backlash
M - Return Mechanism Worn/Broken

The good news is that for routine wear, a ballscrew life can be extended for a further period of service by a very straightforward procedure of repair of the ballscrew by a company such as Jena Tec. Firstly, the ballscrew is checked for its initial condition, this includes checking its free running condition and the "as received" pre-load or drag torque. The ballscrew then undergoes a 32 point healthcheck to check the major points contributing to the ballscrew performance. You can see some of the major areas of inspection referred to above.

After extensive cleaning and checking, the ballscrew, if repairable, is polished along the length of the ballscrew track and undergoes ultrasonic cleaning of the ballnut coupled with high pressure washing to remove baked on grease and grime. The ballscrew assembly is then re-built with oversized micron graded precision ball bearings to achieve a satisfactory level of pre-load along the length of the ballscrew according to DIN specifications.

The unit is then put on extended test and Jena Tec facilities include the ability to document and test the ballscrew running performance on motorised testing rigs. Where a ballscrew passes, a complete documented test report is provided for the customer detailing the received condition and the pass criteria with drag torque graphs and certificates of conformance. Based on Jena Tec's expert assessment, the unit is warrantied with recommendations for the customer on the extended life period.

While many claim to offer ballscrew track re-grinding, Jena Tec advise that due to a weakening of the induction hardened surface and also the cost to re-grind, that in most cases it does not make economic sense to re-grind the ballscrew track form. It is however feasible to re-furbish bearing end journals by hard chrome plating or metal spraying and then re-grinding with a precision universal grinder to exacting bearing fit tolerances. Fixing thread forms are always checked, cleaned and re-furbished where possible as well as wiper seals, fixing key ways and a variety of related small details.

What happens when the ballscrew is not in a repairable condition? Not all is lost, as most ballscrews can be repaired to give a shorter extended life, but in this instance Jena Tec would not offer a warranty but strongly recommend the customer buys a new replacement unit. Jena Tec's extensive stock of precision ground, rolled and whirled product means that we can offer a matched replacement sometimes within the same working day to provide an OEM quality replacement ballscrew.

This means that Jena Tec has the ability to support not only your repair requirements but also your spare parts backed up by our highly trained linear motion technicians, high stock levels and capable precision machine shop.

Typical makes and types of ballscrew repaired by Jena Tec include;

THK NSK Steinmeyer Mannesmann
Hiwin PMI ABBA Comtop
20th Century TCM Blis Berger Bosch
SKF PSI Saginaw Nook
Rockford Nachi Thompson IBL Star
Shuton Iperanga Korta LSI
Barnes American Ballscrew Warner Electric


For service and support on design, selection, repair and replacement of ballscrews and linear motion from Jena Tec go to www.jena-tec.co.uk or call our UK office on +44 (0)1623 726010

XLF Ballscrews Extend Machine Tool Life

Ball Screws are mechanical devices for converting rotary motion into linear motion and vice versa. Ball Screws have become an integral part in modern machine tools due to their positional accuracy, load bearing characteristics and low friction when compared with lead screws, however little has changed in design since the first use of the ball screw in machine tools some decades ago. A common misconception is that to improve a ball screw all that is necessary is to improve lead accuracy, whilst improvement in lead accuracy is important, there are many areas in which design improvements can have significant impact on overall machine performance.

Therefore, the ball screw cannot be considered in isolation but as one element influencing servo loop performance. In developing their new XLF™range ball screws, Jena Rotary Technology Ltd have recognised the importance of the ball screw in servo loop performance, and designed a ball screw to meet the demands of modern machine tool controls. One important factor to consider is reversal error, (reversal error occurs when lost motion is apparent during change of rotational direction in the ball screw) which can affect positioning and surface finish in the work piece. The reaction of the mechanical elements in a system can have a significant effect on reversal error.
The unique design of the XLF™ has produced a ball screw with extremely low coefficient of friction whilst retaining high system rigidity and eliminating reversal error. Due to the design and materials used, it has also been possible to reduce the preload in the ball nut whilst retaining rigidity. Ball Screw life, and wear accuracy have also been significantly improved, the ball screw is also extremely quiet compared with traditional designs. Another benefit is thermal stability of the assembly due to the reduced preload, improved rigidity and low coefficient of friction, producing a ball screw with extraordinarily low levels of heat generation.
These improvements have been achieved using hybrid materials and changes in the design of the raceway profile in the ball screw and the ball nut, the changes are not noticeable to the eye with the exception of the blue/grey appearance of the ball screw, and the reduced preload and super smooth run can be felt when the ball nut is turned by hand.
Clearly these benefits are not restricted to the machine tool industry; any applications where high accuracy, extended life and low levels of noise are required would benefit from the advantages the XLF™ range ball screws offer.

For more information on the Jena Tec range of ballscrews, spindles and linear motion products and services, contact our sales team on +44 (0)1623 726010 or sales@jena-tec.co.uk or http://www.jena-tec.co.uk/

Jena Tec Assures OEM Spindle Test Quality

Jena Rotary Technology Ltd (Jena Tec), part of the Avingtrans plc Technology Group, saw the final installation and commissioning of a state of the art PC based Bosch test facility for motorised spindles in its Nottingham facility in May 2006.
Jena Tec is a leading UK supplier of ballscrews and machine tool spindle repair and replacement services to the aftermarket, OEM and factory automation industries and through the investment will be able to provide customers with a quality assured documented test programme.


Conventionally, machine tool spindles are tested using individual manually operated test equipment which requires operator intervention and is laborious to document, limited in scope and can be subjective in terms of interpretation and operator recording.
The new Jena Tec Bosch test rig allows for each spindle to have a unique record and test programme which is automatically programmed through a range of test cycles unmanned. Specific data can be captured and functionality of the spindle tested including;

•Motor Current logging
•Automated run in procedure
•Bearing Temperature & Lubrication
•Vibration Monitoring
•Encoder Performance
•Tool Clamp/Unclamp either hydraulic or pneumatic
•Drawbar switch setting
•Hydraulic actuation
•Cooling efficiency
•Air purge operation


What this means to machine tool customers, be they in the Aerospace, Automotive, Woodworking, Oil/Gas or precision engineering industries is that they can be assured of an OEM standard quality test programme for their repaired spindle. This can be subsequently audited and tracked to their specific test programme providing a higher level of assurance in the work conducted by the spindle repairer.


Jena Tec supply spindle and ballscrew repair services for a wide range of machine tool, machinery and special purpose automation. For more information contact Jena Tec at sales@jena-tec.co.uk or on +44 (0)1623 726010 or go to http://www.jena-tec.co.uk/