In AGMA 913-A98 figure 3 the helix angle β is shown in a plane that is not the reference plane. Is this an error?
AGMA 913-A98 figure 3 is correct. The angle β shown on the drawing is between the normal plane of the hypothetical rack and the transverse plane of the gear, and this angle does not change with diameter. The amount of profile shift does not affect this angle. Some confusion may exist since the helix angle of the gear varies with diameter and is only equal to the angle of the rack at the reference diameter.