Rod end bearing

A rod end bearing, also known as a heim joint (North America) or rose joint (UK and elsewhere), is a mechanical articulating joint. Such joints are used on the ends of control rods, steering links, tie rods, or anywhere a precision articulating joint is required, and where a clevis end (which requires perfect alignment between the components) is unsuitable. A ball swivel with an opening through which a bolt or other attaching hardware may pass is pressed into a circular casing with a threaded shaft attached. The threaded portion may be either male or female. The heim joint's advantage is that the ball insert permits the rod or bolt passing through it to be misaligned to a limited degree. A link terminated in two heim joints permits misalignment of their attached shafts.

Male threaded heim joint
(A) Casing
(B) Ball swivel
(C) Opening for attaching hardware
(D) Threaded shaft

A linkage with heim joints on both of its ends transmits force in one direction only: directly along its long axis. It cannot transmit forces in any other direction, or any moments. This makes these types of joints useful for statically determinate structures.

History

The spherical rod end bearing was developed by Nazi Germany during World War II.^[1] When one of the first German planes to be shot down by the British in early 1940 was examined, they found this joint in use in the aircraft's control systems. Following this discovery, the Allied governments gave the H.G. Heim Company an exclusive patent to manufacture these joints in North America, while in the UK the patent passed to Rose Bearings Ltd.^[2] The ubiquity of these manufacturers in their respective markets led to the terms heim joint and rose joint becoming synonymous with their product. After the patents ran out the common names stuck, although as of 2017^[update], rosejoint remains a registered trademark of Minebea Mitsumi Inc.,^[3] successor to Rose Bearings Ltd. Originally used in aircraft, the rod end bearing may be found in cars, trucks, race cars,^[4] motorcycles,^[5] lawn tractors, boats, industrial machines, go-karts, radio-control helicopters, formula cars,^[6] and many more applications.

Adjustability

Female heim joint

Heim joints allow adjustability of the linkage length that they are attached to after assembly and installation. Rod ends are usually manufactured with slightly longer threads than are absolutely necessary, so they can be threaded further onto their mating shaft if needed. This is useful for maintenance, to correct for wear after a period of use, adjusting the link length to compensate for manufacturing tolerances, or fine tuning the performance of a mechanism after it is assembled. After adjustment, the new position is then locked in place with a jam nut.^[6][7][8]

See also

• Ball joint