The Barnes Variable-speed Power-Feed Mechanism employed a slotted leadscrew to drive, through a key, a gear which could be slid into engagement with any one of four ring gears cut on an apron-mounted wheel. The operating lever slid in a long slot milled in the lower part of the apron. To reverse the fed the lever, which was hinged just below its connection with the sliding gear, was swung in the opposite direction and the drive gear moved right across and meshed with the other side of the ring gears.
Power surfacing was also driven by the device, the large gear being pivoted so that it could be raised slightly to mesh with a gear formed on the end of the cross-feed screw