Solid Carbide End Mill Coatings, Grades, and Geometries CNCCookbook
Imagine the angle between the edge of the helix (the spiral flute) and the flat bottom of a standard endmill. A low helix endmill has an angle of 35 degrees or less whereas a high helix endmill has more than 35 degrees. A good roughing + finishing in one cutter compromise is a 38 degree helix angle.