I generally find that the Sorby hollowing tools (and Easy Wood hollowers) are not shaped correctly. A well-formed hook tool has the cutter in line with the shaft, and the radius of the hook is NOT symmetrical. Rather, the curve is relatively tight near the cutter and much more gradual near the shaft. Look at a John Jordan, Trent Bosch. McNaughton or Lyle's tools and you will see correctly formed hooks. Same for Hunter tools.