When the screw cutting hits a stop set on the lower bar, the feed disengages, ans sets up a retactor and the carriage rapid feeds to the origin. The operator then disengages the retractor, dials in the next cut and engages the feed - lind of a very primitive mechanical CNC. The extra clutch and return is probably in need of a rebuild if it hasn't been used in a while. They were known to be difficult, breaking down often in industrial uses. \
-- If I had any room at all I'd be there to buy it. they were never very common.