Having used the Neway cutters as seen here, in the past, I can tell you a bit about them. They make an excellent job and are for set angles. The engines we work on are mainly 30 and 45 degree valves, that means that the seats are cut one degree different, ie cutters are 31 and 46 degrees. The cutter as two angles, just turn it over for the other one, you will see this in the photos. The diameter of the cutter can be adjusted by releasing the locking screws and sliding the cutters out. Whatever you do, you must have unworn guides as the cutter cannot centralise on the seat.