Ball or roller bearings have theoretical point or line contact with their tracks and the actual contact area is therefore very small. Especially when subjected to high loads at low speeds (typical operating conditions for woodturning lathes), the boundary film provided by the lubricant breaks down. The load then forces metal-to-metal contact within the assembly. The damage is cumulative and limits the life expectancy of any rolling element bearing. (Also, the necessary working clearance in all such assemblies allows the rolling elements to generate noise, which worsens as the bearing ages.)
     P recision plain bearings by contrast "float" the shaft in a thin film of lubricant and, because the curvature of the adjacent surfaces is practically identical, are capable of carrying hugely increased loads without ever allowing contact between the shaft and the supporting faces of the bearings. In fact, the special lubricant used for the VB bearings provides a boundary film resistance that will withstand load pressures at the interface in excess of 200,000 pounds per square inch. The VB's main bearing alone has an internal surface area of more than 20 square inches so could probably withstand the force of a small nuclear event! The necessary working clearance between the shaft and the supporting bearings is completely taken up by the lubricant film so that the shaft has no detectable play.
      A difficulty for manufacturers who want to take advantage of these benefits is that there is zero allowance for misalignment of the bearing housings in a linear plain bearing system. Traditionally, such bearings were therefore fitted undersize, then reamed simultaneously in-line to open them out to the required dimension. However, the reaming  process itself could degrade the bearing surface. We solve the problem by using of one of the most advanced machining centres in the world to ensure that the alignment and surface finish of the VB's mainshaft bearing assembly is "perfect". (See Video.) This machine actually monitors its own performance to an accuracy of better than 5 microns on any axis! (A micron is one thousandth of a millimetre.)
      Phosphor-bronze is the material most people think of when considering plain bearings and, if lubrication is uncertain or infrequent, this may indeed be an appropriate choice. Where permanent lubrication is provided for however, cast iron has positive advantages in that it can be ground to the finest tolerances and has virtually indefinite working life. VB bearings are machined from a special grade of solid cast iron billet that has been precisely formulated for such bearing duties. Oil reservoirs and galleries are provided above and below the shaft and distribute oil evenly over its surface as it rotates. Oil seepage outside the bearings is inhibited by isolating the journals within spring-loaded, twin lip, high temperature seals and protective steel covers.