Device for Facing Bulky Work on a Lathe

This is a design of engineer T. V. Thong, Hanoi, Vietnam, in 1963.
Work (not shown) is fixed to lathe cross slide.
Yellow body is fixed to lathe spindle through its tape-tail.
Pink worm has revolution joint with the body.
Violet nut - worm wheel, which is in mesh with the worm, can rotate around cross axis of the body and around the worm.
Orange cross screw, which is in mesh with internal thread of the nut - worm wheel, is fixed to blue slider carrying red cutter.
Cyan clutch controlled by green shifter has sliding key joint with the worm.
Brown half clutch is fixed to lathe base (stationary).
Yellow half clutch is fixed to yellow gear that receives motion from lathe feed gearbox.
When the lathe spindle rotate (not shown its transmission train) the red cutter moves following Archimedean spiral for facing the work.
The separation distance T of Archimedean spiral can be adjusted by selecting speeds or directions of the yellow gear and positions of the cyan clutch.
The video shows how T is increased: at first, the cyan clutch is at right position, the worm is immobile, then the cyan clutch is at left position, the worm rotates together with the yellow gear.
It is possible to adjust radial position of the cutter by turning the orange screw when keeping the nut - worm wheel immobile.
Positioning device of the green shifter is not shown.