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Production efficiency: it's all down to Experience

What does the late John Entwistle of The Who have in common with Dave Best of indie rock band The Pigeon Detectives, or Glen Matlock of the Sex Pistols with Rupert Jarvis of The Maccabees?

The answer is they are all bass guitarists with a strong preference for Rotosound guitar strings. The sound quality of this Kent-based manufacturer’s guitar and bass strings has made it 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 have counted amongst its customers.

This enviable reputation derives from the careful choice of raw materials and the bespoke winding process that gives the strings their distinctive sound.

The process is fundamentally the same today as it was when the current Chairman’s father started the business in the ‘60s.

Also unchanged is the 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.

Rotosound came into being as a result of zither collecting.

Having learned to play the instrument in the Army, James How started to buy old zithers, many with missing strings. As a typical instrument can require up to 150 strings the need to mechanise the winding process became apparent to make restoration viable. As he was working at the Royal Ordnance Factory in Woolwich at the time, James had the means to design and make the machine which was ultimately to form the basis of his guitar string business.

“The late ‘60s was a good time to start,” says Jason How, the founder’s son and Chairman of Rotosound since the mid-’90s.

“There were virtually no imported US strings into the UK so the potential was considerable.” The reputation of Rotosound’s products travelled with those bands and a global market soon opened up for this Sevenoaks-based company.

The first generation of the Rotosound winding machines were highly labour intensive. The wire had to be fed manually and the 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 to 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 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 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 allows the carriage to run true and steady — vital to maintaining the constant tension of the core and wrap wires and their respective feed angle.

Rotosound went 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 mounted in parallel with a set of bearings on each slide track which carries the wire feeder mechanism. Like the original slides, the GV3 runs dry to keep the process as clean and friction-free as possible: recirculating systems need regular lubrication intervals and are therefore not maintenance-free.

A key benefit 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/sec, Jason cannot recall having to adjust for this purpose.

Clearly the machines need to handle different gauge wire, each having unique operating parameters, but the linear system has been permanently set for the highest load and the greatest tension.

The successful design of the new semi-automated machine has led to a further ten units going into production. Their introduction has added £0.25m of additional product sales with no increase in labour cost. These machines are producing 60 to 80 strings/hour – more than twice that of the manual version – and are responsible for over 95 per cent of Rotosound’s output.

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