That cutter is a gear, and it is cutting a gear. Gear shaping is a generating process. The tool is a hardened pinion with relieved flanks and ground rake, and it reciprocates along the axis of the blank while both cutter and workpiece rotate in a fixed timed ratio. Nothing on the machine holds the shape of a tooth. The involute profile appears as the envelope of hundreds of overlapping straight cutting positions, exactly the surface two meshing gears would roll against each other. The plate on this machine reads ВНУТРЕННИЙ, meaning internal, which is the entire point. Hobbing is faster for open external gears, but a hob is a worm and needs run out clearance to sweep past the face. Inside a ring gear there is no such room. A shaper only needs the length of the stroke plus a shallow undercut groove, which is why internal ring gears in planetary drives, wind turbine boxes and automatic transmissions are almost always shaped. The details that make it work: - The cutter withdraws a few ...