What Is a Rake Angle?

A rake angle is a measurement used to describe the slope and position of a cutting tool in relation to the object being cut. Given the wide variety of tool designs, rake angle refers specifically to the angle between the head or cutting tip of the tool and the work surface. This measurement can be applied to both hand tools and machinery, including lathes and milling machines. It is used to create the proper cuts in wood, metal, and composite materials, such as plastics or ceramics. Rake angle is typically measured in degrees and can range from zero to 180, though values generally fall more towards the middle of this range, as it can be difficult to cut with the tool at an extreme angle.

To understand how a rake angle works, picture a piece of wood lying parallel to the ground, with an imaginary line pointing straight up at 90 degrees from the wood. A cutting tool placed directly on top of this line would have a rake angle of 90 degrees. If the cutting edge of the tool is in front of the line, moving towards the line as it cuts, it is said to have a positive rake. If the tool is positioned behind the line, moving away from the line as it cuts, it is said to have a negative rake. Positive angles are obtuse, measuring more than 90 degrees, while negative angles are acute, measuring less than 90 degrees.

A positive rake angle is desirable when working with standard objects like wood and steel. This technique requires less power and force from a cutting machine, while still removing large volumes of material. It also requires less effort when cutting objects by hand. Negative cutting angles generate extreme cutting force that can be tough to control, making this technique better suited to very hard or dense materials. A tool held at a positive rake angle pushes towards the leading edge of the object being cut, while a tool at a negative angle pulls or scrapes excess material towards this leading edge.

Certain types of cutting machines, such as a lathe or a milling machine can cut materials along multiple axes at the same time. These machines thus have two separate rake angles to consider. The axial rake is measured from the cutting edge of the tool to the axis of the machine's spindle. The radial rake is measured from the edge of the tool to the casing of the machine itself. These angles can be described as positive-positive, negative-negative, or positive-negative, depending on how the two tools are positioned.

Rake angle serves as a critical piece of information for workers in a variety of industries. These angles apply to mining and earthwork operations, as well as manufacturing. In metalworking, milling, and woodcrafting, workers must understand how rake angles work and how to position tools to achieve the required angle.