Air Bearing SP-150 Work Spindle and C-axis with 8 Inch Vacuum Chuck
The SP-150 is Precitech’s high accuracy work holding spindle, axial and radial error motions under 25 nanometers. The speed control is variable, closed loop, and bidirectional up to 7,000 RPM. This air bearing spindle is constructed using a hardened stainless steel shaft and bearing bronze bushings. These materials provide a durable spindle that provides many years of operation without maintenance or servicing. A DC brushless motor is mounted integral with the shaft, as is the velocity feedback encoder and C axis position encoder. Passages are provided for coolant circulation to maintain thermal stability both in the motor housing and the bearing housing. A passage is also provided for vacuum or air pressure to be supplied through the air bearing and to the face of the spindle for fixturing.
The C-axis includes Slow Tool Servo software, a high resolution encoder fitted to the work spindle, and encoder outputs for use by a Fast Tool Servo. Slow Tool Servo (STS) is used for rapid manufacture of departure freeform components. The Slow Tool Servo relies on the machine tool's slide ravels to actuate the tool holder synchronous with the rotation of the C-axis spindle and cross slide thus creating a system with the ability to perform large departures at slower speeds. Different from the FTS, the tool position of STS is precalculated and commanded as three coordinated axes of motion on the machine controller.
Fixturing diamond turning parts in a stress free state is difficult. The vacuum chuck is provided with a flat front face that can be diamond turned in place on the machine. This provides a nearly perfect flat surface for fixturing. The vacuum chuck provides a fixturing method that will not stress the part if the back side of the part or fixture is also made flat. The diameter of the vacuum area is adjustable to match the diameter of the fixture provided. A central dowel pin is also provided for initial alignment and safety. Vacuum is not lost upon power failure or E stop for safety reasons, but vacuum will be lost upon failure of the compressed air supply to the machine.
