KentTeffeteller
Gimpus Stereophilus!
OK, I understand that part as well. the groove walls aren't at an incline induced from the rake angle of the cantilever holding the cutting blade. The cutting blade was still perpendicular to the plate. The increased rake angle of the cantilever allowed more down force to be applied to the cutting blade, without adding more down force to the cutting head. Or another way to look at it, they could reduce the downforce some of the cutting head while retaining the downforce of the blade.
The cutting heads changed their angle at which the grooves were cut, from 15 degrees to 20 degrees as a baseline. The record industry were trying to standardize the tracking angle, in the name of improving record playback.