What is the term used for a rake angle that results in a top surface of the cutting edge perpendicular to the centerline of the workpiece?

The correct term for a rake angle that results in a top surface of the cutting edge being perpendicular to the centerline of the workpiece is known as a zero rake angle. This means that there is no inclination of the cutting edge relative to the workpiece.

At a zero rake angle, the cutting edge is parallel to the workpiece's surface at the point of contact, which can be beneficial for certain machining operations as it provides stability and can reduce the cutting forces acting on the tool. This orientation helps in achieving a flat cut and is particularly useful in applications where a smooth surface finish is required. The use of a zero rake angle is common when dealing with hard materials or when a stronger cutting edge is desired to withstand the stresses of cutting.

In contrast, other rake angles, whether positive or negative, indicate an inclination that alters the geometry of the cutting edge. Positive rake angles typically improve cutting efficiency and reduce cutting forces by enhancing chip flow, while negative rake angles can increase tool strength but may lead to increased cutting forces and heat generation. Acute rake angles describe a specific desired slant of the cutting edge but do not imply a perpendicular relationship to the workpiece centerline as zero rake angle does.