Full control

Today’s gears are tough, reliable and accurate components used in a wide variety of applications, from rotary table drives to the music industry. Mark Venables reports.


Gears and gear mechanisms are probably among the oldest mechanical technologies known to man. Early examples include simple wooden gears used in potters’ wheels, while stone and metal ones were used by the Greeks and Romans.

Today’s gears are high-precision components used throughout industry. Based on advanced metals and composites, they provide a tough, reliable and often exceptionally accurate method of controlling shaft rotation rate and direction of rotation, or of converting rotary to linear motion.

‘In many respects, the development of gear systems mirrors that of industry as a whole, with an ever-growing need for greater machine and component performance at an increasingly competitive cost. This changing demand has led to the evolution of a number of new gear technologies,’ said Graham Mackrell, UK sales director of Harmonic Drive.

In one example of modern gear technology, German machine builder Ruckle — which manufactures positional indexing, rotary table drives used for accurate work holding when fitted to turning or milling machines — has chosen Renold Gears’ Holroyd dual-lead gears.

These dual-lead, wormgear sets are ideally suited for use in positional machinery as they provide a kinematically correct gear that can run in either direction of rotation and on which the backlash is infinitely adjustable from an acceptable maximum to zero. The gears are manufactured in matched pairs and the mounting diameters are designed to fit to the customer’s requirements.

Transmission testing of the profile of the gears ensures a constant contact throughout its full rotation. This comprises a continuous measurement of the angular position of the driven wormwheel relative to where it should be with a perfect gear set as the driving worm rotates at a uniform rate. The test measures, and records directly, pitch and eccentricity errors, and also the profile errors of the active part of the profile.

Another example from Renold is a huge wormwheel, the largest manufactured by the company, which has been achieved by cloning a worm currently operating on a huge pulveriser drive at a coal-fired power plant in the US. In this instance, however, it was not new technology in the gear itself that was impressive but the ability to replicate an existing component.

The phosphor-bronze wheel is 2.4m in diameter and weighs in at just over four tonnes. The pulveriser grinds the coal to fine dust before it is mixed with warm air and blown into a furnace, where it ignites.

The wormwheel was manufactured as a replacement for one that was coming to the end of its working life but because Renold did not manufacture the original, the company had to ‘reverse engineer’ the tooth form of the gears in the US for virtual cloning at its Milnrow plant in Greater Manchester.

In a worm and wheel set, the teeth must mesh to give a perfect contact and the precise measurements of the profile of the teeth are critical. So it was crucial for Renold to ensure that the wheel manufactured at Milnrow would mesh precisely with the worm gear at the US power plant.

Each gear manufacturer cuts its gears to its own tooth form and without having these details the gears have to be copied using a precise method of back engineering.

This was achieved by taking an exact impression of the mating wormshafts thread profile in a perfect mould, known as a slug. It was then sent to Milnrow where it was measured using the latest co-ordinate measurement machine loaded with Renold’s unique software package.

This maps the slug precisely and creates a computer model of the original worm’s thread profile. From this, Renold was able to manufacture a master worm and the tooling with which the new wheel could be hobbed. After hobbing, the wheel was paired with the master and adjusted to get the optimum profile to create a perfect clone of the original wheel in the US.

The world of rock music would, on the face of it, appear to be the place you would least expect to find the innovative use of gear technology. but that is exactly where Berkshire’s Maxon Motor found a use for their guitar tuner from Somerset-based ATD.

The idea for a completely automatic tuner, which removes the hassle of manual tuning, has been developed by a team including ATD director Trevor Wilkinson, head of design engineering Andy Leadbetter and managing director Richard Whittall. The device, which is claimed to automatically tune an electric guitar to a faultless pitch, is a project the team has been working on for some years. It has come to fruition thanks to the help of some crucial components sourced from Maxon.

The strings need to be put under a certain amount of tension to begin with. Then, at the flick of a switch, the S440 tuner kicks in and, at the first strum, all the strings are tuned perfectly with an LED display confirming the accuracy.

Not surprisingly, to be commercially successful the tuner needs to be almost unnoticeable to the guitarist (except when needed, of course). On a standard Fender Stratocaster, for example, the system fits neatly into the space left by the original bridge — even down to using the original screw holes.

As part of the design process, it was important for the designers to incorporate the tiniest, yet most reliable, gearing into the system. ‘We supplied a block of six gearheads, to which the motors in the device are fitted,’ said Maxon’s chief executive Keith Ellenden. ‘The gearheads are made using the very latest metal injection moulding (MIM) technology, which allows a high level of sophistication in miniature,’ he said.