Positive feed tools and methods of use that include a spindle with a distal end configured to receive a tool bit. The spindle is movable in a forward direction for the tool bit to act on a workpiece, and a retract direction to move the tool bit away from the workpiece. The spindle is configured to retract to a home position at which an air motor that drives the spindle is shut off. The feed tool includes a clutch to prevent jamming of the spindle at the home position in the event the air motor is not shut off at the proper time.

An air control device includes an air suction port, air discharge ports, and an air control system. The air suction port takes in air. The air discharge ports discharge the taken-in air. The air control system discharges the air through the air discharge ports alternately for respective preset times. An air control method includes: taking in air; and discharging the air alternately through air discharge ports for respective preset times.

A positive feed tool that includes a spindle that is axially moved along a feed path to perform work on a workpiece. The tool includes a gear head with a plurality of gears configured to rotate and axially move the spindle. The gear head is designed to change the changing gears within the gear head to change feed rates on the spindle. The gears can be interchanged without a complete disassembly of the gear head.

A spindle unit includes a casing defining a spindle housing space, a spindle housed in the spindle housing space with a gap from an inner wall of the casing and has a first large-diameter part and a second large-diameter part separated from the first large-diameter part in the axial direction, a motor coupled to a base end part of the spindle, a high-pressure air source, and a valve between the air source and an air supply path. When the valve is opened to introduce high-pressure air into the gap and the motor is rotated and the rotation speed of the spindle becomes equal to or higher than a predetermined rotation speed, the controller closes the valve to interrupt supply of the high-pressure air into the gap and the spindle is rotatably supported by a dynamic pressure air bearing enclosed in the gap and is dragged by the spindle's rotation.