Arming a lathe with live tooling offers the chance to completely machine a part in one setup. However, live tooling may not provide the very high speeds necessary for some grinding, polishing, engraving and small-diameter drilling operations. If a part must be transferred from a “multitasking” lathe to one or more additional machines for such high speed operations, then the lathe does not realize its done-in-one processing potential.
To optimize lathe capabilities to include very high speed machining operations, NSK America has integrated a non-contact air bearing into its air-powered spindle design to allow speeds up to 160,000 rpm.
The air bearing provides rigidity and runout that can accommodate tight-tolerance machining, but light cuts are required. For the lowest speed model (60,000 rpm), the maximum cutting power is 40 watts. The spindles accept drills as small as 0.5 mm, which are commonly used for hole making on medical and electronic components.
Compressed air entering the air bearing spindle is divided into two paths—one to rotate the spindle and the other to support the spindle in the bearing chamber. The spindle and air bearing race are precisely machined to allow 0.02-mm separation between surfaces.
Spindles using air bearings must be “floated” before they can be rotated. That is, air pressure must first be applied to the spindle to create the cushion between the spindle and bearing race. This can be done manually, with an air valve, or automatically, by programming the control to send an M code that will activate a solenoid air valve.