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Technology in Action

Linear slides

over the rock generations

Posted on April 1, 2008 - ( views)

by Web Editor

What does the late John Entwistle of The Who have in common with Dave Best of the indie rock band The Pigeon Detectives or Glen Matlock of the Sex Pistols with Rupert Jarvis of The Maccabees? The answer isthey are all bass guitarists with a strong preference for Rotosound guitar strings. The sound quality of this British manufacturer’s products has made them the choice of successive music generations and photos on Rotosound’s sales office walls give a glimpse of its celebrity status. Jimi Hendrix, ELO’s Jeff Lynne, 10CC’s Eric Stewart and Iron Maiden’s Steve Harris count amongst its high-profile customers.

This reputation derives from Rotosound’s careful choice of raw materials and the bespoke winding process that gives its strings their distinctive sound. The process itself is fundamentally the same today as it was when the current Chairman’s father started the business in the ’60s. Also unchanged is Rotosound’s use of HepcoMotion linear slides to guide the cradle that carries the wire spool set. Indeed the Generation 1 Hepco slides that were specified for the first winding machines are still working today, more than 30 years later.

The first generation of the Rotosound winding machines were highly labour intensive. They required the wire to be fed manually and their throughput was just 20 to 30 strings per hour. The process involves wrapping various types of cover wire over a choice of base core wires and then, in many cases, gluing on a final layer of silk. As demand for the product has grown so too has the need reduce labour costs, improve consistency and increase output. That is precisely what the latest design of the ‘How’ winding machine has been designed to do.

The basic mechanics of the original machine remain relatively unchanged. As Jason explains, ''Why change a system that is working well?'' What was needed however was the introduction of a programmable electronic drive to improve the consistency of the feed and improve productivity. Thanks to its ‘vee’ profile and bearing set-up the design benefits of the original Generation I Hepco slide remained central to the friction-free movement of the carriage plate and overall rigidity of the system. So in specifying elements for the prototype of the semi-automated version of the machine, Jason naturally chose Hepco again. In Jason’s words the products have been key to how he has been able to develop the machine.

''In truth I have never considered any systems other than Hepco. I know of designers who have used recirculating technology in the way of shaft and ball bushings but I didn’t feel this could give me the rigidity I needed. There was danger of deflection in the end supported shafts, any load could cause the shaft to wobble,'' Jason adds. Rigidity, allowing the carriage to run true and steady, is vital to maintaining the constant tension of the core and wrap wires and their respective feed angle.

Rotosound has gone straight from Generation I Hepco slides, skipping a whole generation introduced in the ’80s, to the latest GV3 System for the new machines. The only specification change has been the introduction of a dual slide system that is mounted in parallel witha set of bearings on each slide track which carries the wire feeder mechanism. In common with the original slides, the GV3 System runs dry to keep the process as clean and friction-free as possible; by comparison recirculating systems need regular lubrication intervals and are therefore not maintenance-free.

Another important design benefit of both generations of Hepco systems is their eccentric adjustment that allows pre-load to be controlled simply to acquire the necessary rigidity on the carriage plate. Compensation for wear can be accommodatedin a similar way but as the winding traverse only requires linear speeds of just 50 -70mm/sec., Jason cannot recall having to adjust for this purpose. Clearly the machines are required to handle different gauge wire – each having unique operating parameters – but the linear system is permanently set for the highest load and the greatest tension.

Although the winding machine does have a cover to help prevent glue and debris falling onto the slide tracks the HepcoMotion design is inherently able to cope with such ingress as the vee-profile is essentially self-cleaning. A recirculating system by comparison relies on seals/scrapers to remove any deposits. However there is always risk of the seals failing to exclude the debris resulting in contamination of the recirculating pathways and compromised running quality. Along withthe introduction of the HepcoMotion GV3 system came cap wipers, devices that provide positive lubrication and enhance the self-cleaning operation of the vee-profile. However, true to his father’s original design, Jason chose not to include this option as he was determined to keep the system as simple as possible Also as the Generation I system worked well without them, why shouldn’t GV3 too?

The successful design of the new semi-automated machine led to the building of a further ten units that went into production last year and their introduction has added £.25m of additional product sales with no increase in labour cost. These machines are producing 60 – 80 strings per hour – more than double that of the manual version – and responsible for more 95% of the company’s output.

There is no longer any need for training on specific products as, once set-up, the machine is responsible for holding all the necessary operating parameters. The payback on each of the new semi-automated machines is projected to be just two to three years and each unit effectively saves one operator. ''And crucially the quality of our manufactured product is much more consistent which is of vital importance in the light of demand,'' Jason adds.

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