This is a rocker for my little lathe. I copied mostly from pictures of Gortonís Swiss automatic lathes, but itís less finely adjustable and I made it so I can put different things on it, normally tool posts but also things like my screw slotting fixture.
It has the same function as a cross slide with front and rear tools on a regular screw machine or plain lathe, and like those is limited to in-feeding, but instead of sliding on ways it rotates about 45į on a journal that clamps around the bed. Each side has a small slide to set cut depth relative to the fixed stops underneath, with t-slots for mounting tools that allow some individual sideways adjustment. Springs center it when itís not cutting.
Itís a 3/16Ē tool in the video.