HEIM® Rod Ends: History, Applications, and Styles

Sometimes, there are mechanical joining challenges where significant misalignment is present. In these cases, spherical bearings may not be up for the task. This is where HEIM® rod ends come in. They can accommodate misalignment, and are ideal for situations where you have oscillation, rather than rotation. Today, we’ll review the applications, history and available styles of HEIM® rod ends.

What Exactly Is A HEIM® Rod End?

A HEIM® rod end, often referred to as a HEIM® joint, is a mechanical articulating joint. It offers an alternative to a conventional housing installation. Unlike a spherical bearing, which needs to be put into a housing, the rod end is the housing. This efficient design also makes them easy to mount and adjust. Further, they are compact and lightweight as a result.

A Brief History of the HEIM® Rod End

The HEIM® rod end’s roots extend back to World War II. In late 1941/early 1942, a downed Messerschmitt Bf 109 warplane was recovered by the British and shipped to Vultee Field in California to be disassembled and analyzed. The plane boasted exceptional maneuverability, thanks in large part to an innovative slotted bearing that was used throughout the control system. The bearing was then presented to various bearing manufacturers, including the HEIM® Company in Fairfield CT. The company was founded by Lewis R. Heim, celebrated as a mechanical genius, engineer and inventor. He is also credited for inventing centerless grinding, and many machines and processes used in manufacturing, particularly for the textile industry.

It is said that Heim studied the Messerschmitt bearing for about five minutes before sketching the integral rod end known today as the HEIM® rod end. It was easier to manufacture, more efficient, and composed of less critical material. After intense field testing by the military, the HEIM® company was awarded the contract to supply them, giving the US a notable advantage in wartime aircraft performance. Today, HEIM® Bearings is a division of RBC, (which is also PIC Design’s parent company).

Applications

HEIM® Rod Ends are ideal for linkage type applications, where oscillation is present, and design efficiency is required. They are used in many industries including aerospace, military, transportation, commercial agriculture, residential lawn care, material handling and fluid power, among others.

One popular application you are likely familiar with is on school buses. Hiding in plain sight, HEIM® rod ends are used to open and close the passenger doors. There’s no room here to mount a spherical bearing. Rod ends provide an elegant solution: simply thread the shank into the link and lock it down. As the link moves through its cycle, it will always stay oriented in the same way, in the exact same plane. This allows the door to open and close reliably and consistently.

HEIM® Bearing Styles

HEIM® Bearings are available today in a variety of configurations to suite different needs. The product range includes rod ends with race inserts, high strength two-piece designs, self-lubricating rod ends, as well as high performance styles for more demanding applications.

They are also available with a wide range of finishes, coatings and materials, with optional features such as lubrication fittings, left hand threads, and keyway slots; in both inch and metric sizes. PIC currently offers four main styles as follows:

MHD/FHD Series

Features an engineered thermoplastic race, which provides excellent lubricity without the need for supplemental lubricants. As a result, they are maintenance-free. With this rod end, a 52100 chrome plated ball interacts with the race. They are ideal for applications where a greased lubricated design could cause contamination issues. The MHD/FHD Series are ideal for medical devices, food production, beverage and pharmaceutical applications. They are quiet and have a smooth feel.

Classic 4 Piece HM/HF Series

Features a 52100 chrome plated thru hardened ball, with a low carbon steel rod body. Two brass inserts make up the race. Due to this design, and how it is assembled and compressed, this style delivers the best conformity in the industry. This means you’re not going to find a gap between the outer diameter of the ball and the races, and they move very smoothly and uniformly. These do need to be lubricated, despite boasting relatively low friction and longevity.

MT/FT Series

These are top-of-the-line rod end bearings reserved for the most demanding applications, where material selection counts. They feature a 4340 alloy steel heat treated rod body which is plated for corrosion resistance. The ball is constructed from heat treated 440C stainless steel. Races are heat treated 17-4PH stainless steel. The liner system is approved to AS81820.

MT/FT series Aerospace Standard rod ends are approved to SAE AS81935 (formerly MIL-B-81935). These rod ends are produced in strict accordance with all applicable specifications and are typically used in military and commercial aviation applications. The MT/FT series can be the solution in many industrial applications.

HEIM® Ball Bearing Rod Ends

While classic HEIM® Rod Ends are designed for oscillating loads; HEIM® Ball Bearing Rod Ends are the solution for low friction/rotating applications. The double row, self-aligning bearings accommodate an application’s low torque, high load, and misalignment needs. Both the inner rings and balls are made from thru-hardened 52100 steel. Bearings are lubricated 80 to 100% fill in compliance with MIL-PRF-81322 and MIL-PRF-23827. Rod ends are equipped with PTFE seals bonded to corrosion resistant caps.

The rod end body is selectively heat treated to provide a combination of a fracture tough head, and ductile shank. The raceway is carburized to deliver a high load carrying capacity. External surfaces are cadmium plated, providing both corrosion resistance and thread lubricity. Our ball bearing rod ends conform to SAE-AS6039 (formerly MIL-B-6039).