R Is for Rake Angle

Metalworking Glossary for the Letter R

See the index to the Glossaries here:


  • R-Axis. On a press brake, the vertical movement of the back gauge is considered the R-axis. Some CNC press brakes allow automatic control of the R-axis, and may even control each side independently, considering them separate axes. As seen from the front of the machine, R1 would refer to the vertical movement of the left back gauge and R2 would indicate the same for the right back gauge. The operator can set R1 and R2 at different heights to support oddly flanged workpieces.
  • Rack. An array of gear teeth spaced on a straight bar, usually engaged by a pinion.
  • Rack Shaper. Another name for a geared shaper.
  • Radial. Referring to a direction that extends outward from the center of a circle, a sphere, or a cylinder’s axis.
  • Radial Arm Drill. A radial arm drill is a very large geared-head drill press with a head that can move out along an arm that extends (or radiates) from the center column of the machine. The arm itself can swivel around in a wide arc, allowing the head to drill in a wide range of positions across the face of a stationary workpiece, even several feet away from the center of the machine. 
  • Radial Cutting Force. In milling, it is a cutting force that is applied to the side of the rotating cutting tool, 90° from the axis of the tool.
  • Radial Rake Angle. One plane of measurement used to determine rake angle (the other being axial rake angle.) Radial rake is the angle between the outside face of a cutting tool and a radial line running from the center of the tool to the outermost point of the tooth. A radial rake angle is considered zero if it matches the radius line, positive if it goes forward past the radius line, or negative if it angles back from the radius line. The angle helps determine the sharpness and strength of the cutting edge.
  • Radius. The measurement of the distance from the center of a circle, sphere, or a cylinder’s axis to its outside circumference.
  • Radius Gauge. Radius gauges are blades that can measure the radius of an object. Several different size radius gauges will often be attached together in a framework resembling a Swiss Army Knife, with convex radii blades on one side and concave radii blades on the other.
  • Radius Grinder. The predecessor of CNC tool and cutter grinders, a radius grinder is a specialized grinder used for processing complexly shaped tools and grinding spherical surfaces.
  • Rake. Also called rake face, it is the surface on a cutting tool that the chips curl up against while being cut. The term rake can also refer to the rake angle of the tool.
  • Rake Angle. A measurement indicating the inclination of the cutting face of a tool in relation to the workpiece. The rake angle, which is measure in two planes (axial rake and radial rake) affects the amount of cutting forces and the strength of the cutting edge of the tool, influencing chip flow and shear deformation. Rake angle is usually different than the lead angle in milling tools, and can be positive, negative, or neutral (called zero rake). Different rake angles perform better depending on type of tool being used (mill, drill, saw, etc.), the material being cut, and the depth of cut.
  • Rake Face Build-up. The accumulation of material from a workpiece on the rake face of a cutting tool.
  • Raker Set. In sawing, it is a tooth pattern where one tooth is set to the right, one tooth is set to the left, and one tooth is unset.
  • Ram. On a press brake, a ram is the moving beam—usually the upper one—that performs the bending action. The term can also apply to the stationary beam that provides the resistance during the bending operation.
  • Ram-type Milling Machine. Any mill with a cutting head mounted on a sliding ram.
  • Ramp Milling. A type of 3D face milling, ramp milling combines a Z-axis movement along with X and Y cutting. It is used to create an angled surface on the workpiece or as the point of entry for cutting a pocket.
  • Ramping. Also known as ramp milling, ramping cuts into the surface of a workpiece at an angle, moving in X, Y, and Z-axes simultaneously.
  • Ratchets. Rachets are gear-like objects with fin-shaped teeth that can only turn in one direction when paired with a spring-loaded pawl that clicks into place after each tooth passes.
  • Reaming. Reaming is a lathe function that expands an existing hole.
  • Recess. A groove or depression in the surface of a part.
  • Reciprocating Surface Grinder. A surface grinder that has the workpiece secured to a rectangular table that traverses under the grinding wheel.
  • Repeatability. The accuracy of a piece of metalworking equipment like a press brake is often measured by repeatability, or the machine’s ability to move the ram or other working part to precisely the same position again and again, allowing the parts it produces to be identical each time.
  • Resistance. A metal’s resilience against being fractured when put under stress.
  • Resultant Rake Angle. Determined by combining the back rake angle and the side rake angle of a cutting tool. Also known as true rake angle or effective rake angle.
  • Right Angle. A right angle is a device, often made of cast iron, that has two precise surfaces set at a right angle to each other. It is used to check squareness and as a vertical reference for inspection.
  • Right-angle Drill. A right-angle drill is a handheld drill with a low-profile drilling head set at a right angle to its body, allowing it to fit into places that are too tight or hard to reach with a traditional portable drill.
  • Right-angle Grinder. Another name for an angle grinder.
  • Rockwell Scale. A measurement of the hardness of a material like metal. It is an indication of how resistant an object is to penetration and permanent deformation from another material. The Rockwell hardness scale is named for machinist brothers Hugh M. Rockwell and Stanley P. Rockwell who invented it.
  • Rotary Axis. Another name for the A-axis, the rotating fourth axis on a mill that has been equipped with a rotary table.
  • Rotary Surface Grinder. A type of surface grinding machine that has a circular table that rotates a workpiece under a grinding wheel.
  • Rotary Table Milling Machine. A mill with a round table that rotates the workpiece around a center axis through a series of multiple cutters set at different heights. Workpieces can be loaded and unloaded continually throughout the operation.
  • Roughing. The rapid removal of material from a blank or section of stock to reduce it to being just larger than the final part, allowing precision machining to then finish creating the part to specification out of the workpiece.
  • Roughness Gauge. Another term for a surface roughness tester.
  • Ruler. In metalworking, precision rulers called steel scales are used for measuring short linear distances.