A colleague of mine used to keep an aquarium with no fish in it. Instead of fish, the tank contained a mitre box. This aquatic novelty was displayed in the reception room of our manufacturing facility for some time. While I’m sure it baffled many visitors, it provided a useful demonstration of my colleague’s point: our mitre boxes were designed for harsh environments.

Our mitre boxes transmit torque via a set of bevel gears and a cast housing. They play a crucial role in transferring the input from the driver through the steering system, often through tight envelopes which assists our OEMs in reducing packaging space and weight. The box must provide a smooth and consistent output for the driver and therefore must be sufficiently sealed for the harsh conditions of under chassis life.

Our mitre boxes can be customised for different applications, with optional mounting interfaces and ratios. If you add in the requirement for performance and durability in extreme conditions, such as freezing temperatures or vehicles with wading capabilities, then the Ingress Protection rating (IP rating) becomes a key part of the specification.

If an engineer had encountered the mitre box in a fish tank, they might have said: “Well that looks good, but what is the IP rating?”

A look inside the box

To understand the need for customisation, high quality materials and rigorous testing, it is worth looking inside the mitre box to better understand the internal components we are protecting from moisture and debris. Some of the most crucial elements of the box are the gears, bearings and lubrication.

They all play their role inside a mitre box to support the input and output shafts and allow them to rotate smoothly while minimising friction. Lubrication is essential for the smooth and efficient operation of bevel gears and bearings. Water ingress can lead to contamination of this lubrication, which can impact the function of the internal components, causing problems such as increased torque and noise. In the worst-case scenario, water can pool inside the box and when subject to freezing temperatures this results in rapid locking of the mitre box.  Therefore, it is imperative the mitre box is sealed for the lifetime of the vehicle to ensure the effective performance of these critical components.

Whole life costs

Whether you have a military vehicle wading through deep water or a heavy-duty commercial vehicle travelling long distances in freezing conditions, a relatively small intrusion of moisture or debris can cause major issues in your mitre box. The impact might not always be felt immediately, but over time it will result in degradation of the lubricants, increased torque, increased noise and steering issues. Ultimately, it can cause premature failure of the steering components, which can be costly for vehicle manufacturers forced to pay out for replacements.

A mitre box with a high IP rating will be tested to ensure it can offer the right level of ingress protection for the chosen application. The certification process is carried out by a third party to ensure that the parts have been subject to rigorous testing. For military vehicles, a high IP rating is often essential, but for commercial vehicles there might be occasions where the engineer thinks they can save on cost by selecting a cheaper mitre box.

While it’s not surprising that and engineer will want to reduce costs, the savings in these circumstances are generally negligible when compared to whole life vehicle costs. The costs that would be incurred if the part were to fail are vast in comparison. Even a small amount of moisture could result in thousands of pounds of damage if the component failed and needed replacing.

That’s why we design our mitre boxes with whole life costs in mind. We manufacture them in house and secure the third-party testing required to give our customers peace of mind. A good quality mitre box that is designed and tested to be sealed for life should have an IP rating of at least 66 for a commercial vehicle, as it will likely encounter a high level of pressurised water spray. A mitre box that must withstand being fully submerged will need an IP rating of at least 67.

Nick Jordan is Head of Engineering and Quality at steering components manufacturer, Pailton Engineering. To find out more about Pailton’s mitre boxes and view its full range of steering products, visit pailton.com