Linear bearings have been an established technology facilitating linear motion almost since the dawn of time – in a crude form, early man used rows of logs to transport heavy loads, removing the last log and transporting it to the front as the load moved along the ground. Although modern linear ball guide designs are somewhat more advanced, it does not mean they are without constraints.
For instance, ball guide assemblies require the routine addition of lubricants, because without the presence of grease inside their re-circulating ball channels (and along the length of the rail) they will quickly fail. In addition, lubrication can find its way out from behind the sealing system and contaminate the working environment.
Today, a considered alternative to the ball guide bearing is vee bearing/rail technology, which is designed for reliability in environments where other product types fail. Typically, a system comprises a rail, four vee bearings and an anodised aluminium carriage plate for mounting the customer’s components.
Made from hardened and ground high-carbon bearing steel, the rail is accurate, durable, low friction and quiet in operation, while the precision vee bearings are designed specifically for use in linear motion systems. These eccentric bearings can be adjusted in situ to increase or decrease the running preload. In turn, this enables the user to achieve the desired running quality.
Importantly, once the rail starts to show signs of wear it can be adjusted quickly to remove any play and restore the running quality back to its original condition, thus costing nothing in replacement parts. What’s more, if one of the vee bearings fails then it can be replaced individually and not as a whole assembly.
Regarding application, vee guide systems are very tolerant of debris, as opposed to linear ball guides which often fail catastrophically following the ingress of dirt, dust or debris. This is because vee guide systems have a self-cleaning action, which means that any contamination is wiped away by the vee bearings as they run along the rail. The millstone principle is a good reference point, where flour eventually migrates to the outside of the stone as the corn is ground. Similarly, any dirt that lands on the vee rail will eventually get wiped away.
In industries where fine abrasive dust and high levels of contamination are commonplace, like the glass industry, a vee guide system offers clear advantages.
Lubrication is another issue that favours the selection of vee guide systems for those designing machines used in the food, medical or cleanroom industry. It goes without saying that these sectors cannot tolerate the presence of oil or lubrication. Vee guide systems work both with and without the presence of lubrication, largely because the bearings are greased internally during manufacture and then nitrile sealed for life.
Similarly, those designing machines or mechanisms used in high-temperature or vacuum environments will know the difficulties in sourcing the right components to cope in these extreme conditions. Nearly all off-the-shelf linear motion guide systems are made from unsuitable materials. However, vacuum and extreme temperature vee bearings now exist that have been manufactured using only stainless steel for all components – no plastic is used in the assembly.
These bearings are used widely in applications including semiconductor wafer manufacture, aerospace component production, vapour deposition processes, LCD panel and plasma display manufacture, and in vacuum evaporation equipment.
Another inherent disadvantage of linear ball guides is the required precision of the mounting surface. Many manufacturers can testify to the hours spent milling and potentially even grinding mounting surfaces to make them flat and accurate, just so the rails can be fitted properly. Some even try setting up two rails in parallel and CNC drilling the hole positions to get the running quality right.
Conversely, a vee guide system is more compliant, which means it still works effectively when the mounting surface is not machined flat, or two parallel rails are not aligned perfectly. Consequently, a small amount of distortion in the mounting surface will not adversely affect the running quality, especially when fitted to fabricated frameworks or un-machined surfaces.
There is even the option to fit two-piece, ‘twin’-type bearings that yield fractionally to allow for small deviations in mounting surface flatness or parallelism when setting a system, saving hours in time and cost during installation.
Last but not least, non-caged version ballways, which are the general standard, generate significant noise in operation. This is caused by the balls coming in and out of contact with one another. In contrast, vee bearings incorporate caged balls as standard, resulting in virtually silent operation.
To learn more about vee bearing/rail technology go to www.hepcomotion.com.