Not all linear guides are created equal when it comes to delivery times. The highest-precision classes of linear guides usually have dramatically longer lead times, especially at lengths beyond 1240 mm.
For some axes of motion, the most precise guideways are indeed a necessity. But expensive precision products are routinely applied to axes that have less stringent motion requirements. Machine builders have in the past often specified one type of linear guide, usually a recirculating ball type, for use throughout the machine. This approach, while convenient, is no longer sensible or cost effective.
A classic example can be found on CNC machine tools. Motion axes related to cutting may well require the most precise, and expensive, linear guides on the market. The doors, tool-changer and other auxiliary axes are another story. These non-cutting axis may be better off with a roller-type guide that better matches the actual motion requirements–and offers low failure rates, superior alignment and reduced mounting surface preparation as side benefits.
Avoiding overkill on linear motion axes has obvious cost advantages because machine builders end up paying only for the precision they actually need. Less obvious are the supply benefits. Roller guides are almost always available for immediate delivery and can be ordered as needed. Using them where appropriate means there are fewer long-lead time linear guides that can cause delays.