The Difference Bwtween Linear And Box Guideway Vertical Machining Centers

The form of each axis guide of the vertical machining center can be divided into linear guideway and box guideway.

Box guideway vertical machining centers, have been used for centuries. Many styles exist, but you can think of them as a pair of precision ground metal surfaces with a thin film of lubricating oil between them, like a layer of jelly between two pieces of bread; pressurize this oil (as is the case with virtually all CNC machines) and its called a hydrostatic guideway. Most box ways VMC also have a thin layer of Turcite applied to each mating surface, a slippery polymer that helps reduce friction, and most are also scraped, a process that creates small pockets resembling fish scales in the way surface to improve oil distribution.

Linear guideway vertical machining centers are similar to roller or needle bearings, but made flat. In this arrangement, a set (typically four) of bearing trucks is attached to the moving machine element, which then mates up with a pair of rails that have been bolted to the machine casting. As the trucks move up and down the rail, the balls or needles within (depending on the manufacturer) recirculate through the guideway housing, picking up a little lubrication as they go.

As a rule, linear guideway VMCs are capable of higher traverse speeds, often two to three times faster than their boxy counterparts. Because they have none of the stick slip long associated with box ways, they’re generally considered more accurate, although it’s interesting to note that many of the world’s mother machines are equipped with hand-scraped box ways.

Conversely, box ways are usually associated with higher load capacities. They are thought to be more suitable for heavy or interrupted cuts, and better at reducing chatter, although a heavy duty, properly designed linear guideway—especially one that uses roller bearings rather than plain balls—has no shortage of stiffness and rigidity.