The sound quality of the British manufacturer, Rotosound’s products has made it the choice of successive music generations, and the photographs 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 enviable reputation derives from Rotosound’s careful choice of raw materials and the bespoke winding process that gives its strings their distinctive sound. This process is fundamentally the same today as it was when the current chairman’s father started the business back in the 1960s. Also unchanged is Rotosound’s use of HepcoMotion linear slides, which 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 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.
The basic mechanics of the original machine remain relatively unchanged. As Jason How, the founder’s son, 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, Mr How turned once more to Hepco.
“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.” 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 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 with a set of bearings on each slide track carrying 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.
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 accommodated in a similar way but as the winding traverse only requires linear speeds of just 50-70mm/s, Mr How 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.
The successful design of the new semi-automated machine led to the building of a further ten units that went into production last year. These machines are producing 60 to 80 strings per hour, more than double that of the manual version and responsible for more 95% of the company’s output.
Rotosound is currently producing between 50,000 and 60,000 sets of strings per month, containing an average of five strings apiece. “Demand from the US is unbelievable; we can’t make enough for customers out there,” claims Mr How. And one of those customers is Lou Reed - another testimonial to add to the website.