Grip Tight bushings save Garmendale thousands of pounds

Dodge Grip Tight Bushings enable drive wheels to be attached directly onto shafts without the cost of machining keyways and with guaranteed concentricity. The bushing's 360-degree fit and easy disassembly mechanism also simplify routine maintenance, allowing trouble-free removal in seconds, as it eliminates the damage and corrosion that can often be caused by vibration-prone keyway-style couplings with set screws.

Garmendale Engineering specialises in one-off engineering projects and has a considerable reputation in creating trains and rides for the leisure industry, with installations at most of the UK's best-known theme parks. Its latest project in this area is an underground railway system with mineshaft-style wooden wagons. Three trains of four wagons each have been built for the park.

Typically Garmendale Engineering would couple the wheels to the shafts by machining keyways and securing with set screws. The machining and assembly time required for each of the wheels would probably be one to two hours, adding in excess of 50 man-hours onto the total project costs. However, Garmendale became aware of the Dodge Grip Tight bushing system during a routine visit by one of its suppliers - Bearing Transmission & Pneumatics. The significant savings that could be made were immediately obvious.

Simply assembly and disassembly

The simple way the bushing system assembles was also viewed as useful, as it would simplify routine maintenance - allowing the non-specialist maintenance personnel that are often employed at theme parks to remove the wheels without trouble in order to change treads and get access to the bearings. Keyway-style mountings can often lead to fretting damage and corrosion, making wheels very difficult to remove. Keyway systems can also cause vibration, as the set screws usually force the shaft to a slightly eccentric position - shortening the life of bearings. To make the maintenance even easier, Garmendale made up a dedicated C-spanner tool to unscrew the size of Dodge Grip Tight Bushing used, eliminating the need to use a hammer and drift pin or an adjustable wrench.

Each Dodge Grip Tight bushing is made up of two split sleeves and a locknut. The locknut draws the sleeves - which have opposing tapers - together, closing the inner sleeve around the shaft until the grip is tight. This provides a completely concentric 360-degree fit. As the nut is loosened, the spring makes the sleeves open slightly, allowing them to slide off.

For this application, each wagon is independently powered by a compact electric motor fitted with a differential gearbox to accommodate tightly twisting rail track, mounted on a swivelling bogey. The wheels are connected via half shafts fitted with mounted bearings. In this instance, the drive system comes with American shafting, and the typical availability of Dodge bushing in a choice in either metric versions or to American or British shafting specifications.

A wide range of Garmendale's engineering disciplines have been involved in this project, including mechanical, electrical and electronic design, and metalwork and wood construction.

Chris Hurt, Garmendale Engineering's lead engineer on this project, comments: "The Grip Tight bushing has saved us a couple of thousand pounds on this project, and provides a number of performance and maintenance advantages to the end user. The bushing system is ideal for many of the low-speed rotating shaft applications we design for leisure transportation, as well as many other forms of machinery and automation."