One some round-ram machines with the second type of top-column housing  (and they must be very rare), the ram could  not only be rotated by the usual worm-and-wheel arrangement but also to be driven in and out by rack-and-pinion gearing. The rack was cut into the ram and the pinion, formed with a hexagon end, set vertically at the left rear of the turret and arranged so that it could be lifted out of mesh to allow rotation. A small spring-loaded detent pin was provided to hold the pinion in the up-position and was pushed in to re-mesh the gears. The design was simple and only allowed horizontal feed when the head was positioned vertically.
With thanks to Dave Dunbrack in the United States for the photographs.