Monday, November 30, 2009

Intelligent GMN UHS Spindles from Jena Tec UK

In addition to our own manufactured range of high quality B&T customised spindles for milling, turning, boring and grinding, Jena Tec represents a high quality German brand GMN Nuernberg in the UK market for high speed and high frequency machining spindles.

In this issue, we've provided some detail information about GMN's capability in ultra high speed grinding spindles. Conventionally supplied by air bearng spindles which have some limitations and disadvantages in terms of cost and running efficiency, GMN's UHS series provides a robust oil lubricated grinding spindle for exceptionally high speeds up to 250,000RPM coupled with an exacting stability and geometric tolerance. A minimised oil/air dosing system means just the right amount of lubrication gets to the spindle and reduces maintenance and running costs throughout the life of the spindle.

Jena Tec's automation division can offer the UHS series from GMN including integration or retrofit to existing machines. If you would like to discuss how we can offer you the advantage of higher speed and better process performance from your grinding machine, then give our UK office a call on +44 (0)1623 726010 or by email to

Intelligent Spindles from GMN**

Processing small internal diameters with optimum cutting speeds requires high rotational speeds. New GMN spindle ball bearings with very high speed characteristics permit 250,000 revolutions per minute, for instance, with comparatively high spindle rigidity and load capacity. Optimized lubrication of high speed spindles offers great potential for increasing performance. Furthermore on-demand minimal lubrication lowers oil consumption and increases service life. In future integrated data loggers will monitor the condition of the spindle, store the operating parameters and guarantee high availability. GMN has a long track record of supplying a wide range of high frequency spindles of up to 180,000 rpm. However, around two-thirds of the spindles supplied for internal grinding operate with maximum speeds in the 30,000 to 90,000 RPM range.

250,000 RPM for small bores
To operate efficiently, a machine tool spindle must have the appropriate load capacity, rigidity and dynamic run out. In order to guarantee these characterisitcs even for extremely high speeds, the GMN development department was faced extraordinary challenges. Breaking points are reached due to the high centrifugal forces, a compact design has to ensure subcritical operation with sufficient distance to the first critical speed, high precision hybrid ceramic bearings have to be designed specifically for the demands of high speed spindles. These challenges were met wth the the help of current advances in motor technology and the use of further developed GMN spindle ball bearings. It is now possible to efficiently grind small internal geometries with up to 250,000RPM. The GMN grinding spindles used for this purpose have a comparatively large and rigid mounting and a powerful sychronous motor. Consequently, they are not only suitable for special applications at maximum speeds but can also be used flexibly and efficiently in a relatively large rotational speed range.

Integrated lubrication module
These days, ball bearings with permanent grease lubrication or oil/air lubrication are predominantly used in machine tool spindles. Yet both methods have their disadvantages which can be overcome by an innovative micro-dosing system combined with appropriate lubrication strategies. Compared with today's oil/air lubrication method, a significant reduction of the lubricant quantity necessary can be achieved and the systematic performance limits of grease lubrication. I.E. Limited usable life of grease at high temperatures and speed, are to be exceeded. Minimizing lubricant quantities makes ecological and economic sense. It facilitates the inegration of an oil reservoir in to the spindles and ideally requires no more external components. The problems associated with waste oil disposal are also defused. Operating costs of machine tools can exceed acquisition costs several times over if calculated over a normal life cycle. These costs are therefore a decisive factor for many users when making an investment decision. An integrated lubricant cartridge means that high maintenance external components can be dispensed with. The lubricant reservoir only needs to be replaced at relatively long intervals. An almost instant dosage of lubricant ensures that the adjustment of the lubricant quantity matches demand based on the exact measurements of the bearing. This increases reliability and efficiency of the bearing and reduces the quantity of the lubricant needed.

Third generation spindles for machine tools
Spindles are also becoming more and more intelligent. Miniaturised electronics which are integrated in the spindle stores the sensor signals, processes them and reports any exceeding of critical values to the overall machine control system. Important operating data can be accessed during the entire running time of the spindle and can also be analyszed with regard to optimising the process, machine and spindle. In addition, the aim is to go for bearing condition monitoring and consequently early damage detection,based on these intelligent systems is possible. Evaluating temperature sensors, position sensors and vibration sensors will increase precision and productivity of the production process. Additional sensors, on the other hand, harbor the risk of reducing the availability of the spindle system further, therefore, as few additional sensors as possible should be employed and for the time being, a more intelligent analysis of available signals should be aimed for.

** Reproduced from an article by Dr. Bernd Moeller, Head of Engineering Spindle Technology Division at GMN Paul Mueller Industrie GmbH & Co. KG in Nuernberg, Germany.

For service and support on design, selection, repair and replacement of spindles from GMN in the UK from Jena Tec go to or call our UK office on +44 (0)1623 726010

Wednesday, November 25, 2009

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 or call our UK office on +44 (0)1623 726010

Wednesday, November 18, 2009

Jena Tec 50% Ballscrew Repair Discount

We all know the current economic situation, times are tough and maintenance budgets slashed but some machines just have to keep going and need to be repaired. Let us ease the current economic chill just a little and make you aware of our fantastic winter offer for ballscrew repairs.
Send us your failed ballscrew for repair assessment and we will give you a 50% discount off the repair price. All prices are quoted on a standard length and diameter matrix meaning you get a great genuine discount coupled with the outstanding service from Jena Tec.
But don't delay, this offer lasts until January 2010, ring our UK sales office on +44 (0)1623 726010 and ask for your free discount voucher code**.
Then next time you have a ballscrew failure, ship it in, we'll check it over and provide our detailed repair report and commercial offer. If you decide to go ahead place your purchase order and quote your voucher reference, it's that simple, a great discount of 50% on your next repair.
Contact Jena Tec on +44 (0)1623 726010 or email to
Jena Tec repairs ballscrews of any make, type or configuration with whichever type of ballscrew transfer system. Our specialized repair and ballscrew testing facilities mean we can repair ballscrews up to 15m in length and 200mm in diameter. Because Jena Tec design and manufacture ballscrews, we like to think we know a thing or two about ballscrew repair to give the you the customer a first class 1A ballscrew repair. We can offer express ballscrew repair out of hours and while you wait. We can collect your failed ballscrew needing repair or be available to accept your delivery 24/7. Upon receipt of your ballscrew, we log your ballscrew onto our repair system and provide our free of charge assessment report. Measuring critical parameters and conducting a 32 point ballscrew repair check means we offer an unrivalled service for ballscrew repair internationally. Additionally, Jena Tec’s ballscrew repair service technicians can assist with removal and refitting of your ballscrew at your request. Backed up by extensive OEM precision ground, rolled and whirled ballscrew stock designed specifically for the ballscrew repair market, Jena Tec offer rapid reverse engineering and emergency replacement of your failed ballscrew should repair not be possible. Not only that but Jena Tec’s ballscrew upgrade service means that often we can diagnose the failure mode of your ballscrew and offer a drop in replacement with our XLF series precision ballscrews.
Jena Tec offers International, European, UK and USA ballscrews repairs so just give our hotline a call to make arrangements now. It’s as simple as A B C for linear motion and ball screw repair services from Jena Tec. Keep an eye out for our special offers relating to Jena Tec ballscrew repair.
Not only can Jena Tec repair ballscrews, we can also repair your ballscrew and belt driven linear actuators, gearboxes and lifting jacks. Jena Tec’s repair capabilities include hard chrome, re-grinding, reverse engineering and replacement engineering of spare parts within the ballscrew, actuator or gearbox range.
Ballscrews and Actuators Makes & Manufacturers we can repair include;

20th Century TCM
Bosch Rexroth
Thompson IBL
American Ballscrew
Warner Electric

**Terms and conditions apply. Excludes shipping and transportation costs to/from Jena Tec UK. Voucher is valid until 31st January 2010 against new valid purchase orders placed in this period for a single ballscrew repair. Discount is subject to credit and account status. This value is not transferable or available as a cash/credit refund.