The "Releaving Attachment", a common fitting on quality lathes in the early part of the century, was designed to do under power what had previously often been done by hand - to accurately relieve (or back off) the teeth of taps, cutters, hobs and milling cutters.
The device took its power from a gear on the end of the headstock spindle, through interchangeable gears on a quadrant, two knuckle joints and a telescopic shaft, to the actuating mechanism underneath the slide rest.
The device imparted an oscillating motion to the slide, with a cam providing the forward action and a spring the return thrust. The amount of relief needed could be adjusted by turning a wheel at the front of the slide.