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Speeds and feeds refer to the rates at which a tool cuts and material is fed into it. They are important variables in milling, drilling, and turning. Factors that affect speeds and feeds include the type of machine, tool and workpiece materials, and depth of cut. Machining tool manufacturers provide recommended values, but adjustments may be necessary for variables such as tool sharpness and cooling effectiveness. Starting with conservative speeds and feeds can save production time and maximize tool life while producing a quality end product.
The term “speed and feed” is a casual way of referring to the rates at which a mechanical tool cuts and at which material is fed into it. Speeds and feeds are variables of concern in a variety of machining techniques, including milling, drilling and turning. Cutting speed is the difference between the speed of the tool and the surface of the workpiece, whether it is wood, steel or other material and is expressed in units of distance per unit of time. The feed rate is the distance the tool travels in the workpiece for each revolution made by the tool and is expressed in units of distance per revolution. As a form of shorthand, these measurements are sometimes referred to as “feed and speed.”
Speeds and feeds for machining operations depend on a variety of factors. The first of these factors is which particular type of machine is being used. The materials of both the tool and the workpiece are other important variables and are among the easiest for the manufacturer to consider in recommendations. Once these things are decided, it is reasonably easy for the operator to quantify other variables, such as depth of cut.
Milling is the process in which a rotating tool with teeth on one end is fed into a workpiece to remove material from. Modern milling machines can produce a variety of shapes by removing material in all three dimensions. The speeds and feeds in milling can depend on the diameter of the tool and the number of teeth it has.
Drilling drives a rotating bit with a sharp — and sometimes cutting edge — forward into a workpiece to remove material, leaving a hole where the material used to be. Drill bit size is a factor in calculating cutting speed and feed rate for drilling operations. Typically, drill speed decreases as the required hole diameter increases. This is to avoid the risk of burning out the drill motor. The depth of the hole to be drilled also typically reduces the recommended values for these values.
Forming an object by rotation involves clamping its ends in a holding device that rotates it as a cutting tool is advanced into the workpiece. Turning pieces of wood on a lathe in woodworking, for example, can produce items such as table legs, railings, and lamp bodies. The size and shape of the cutting tool used in turning all affect the recommended speeds and feeds for a lathe.
Machining tool manufacturers can provide charts containing recommended values for cutting speeds and feed rates. An operator can choose the values based on the information provided in professional manuals and machining manuals. Formulas are also available for various operations by which to estimate appropriate speeds and feeds. These values, however, are generally general guidelines and not exact specifications.
Speeds and feeds also depend on more difficult-to-quantify variables, such as tool sharpness, operation cooling effectiveness, and others. They may need to be adjusted to account for such variations that cannot be specifically addressed in the manufacturer’s recommendations. A good rule of thumb is to start with more conservative speeds and feeds and adjust as needed based on actual usage. By operating at optimal levels, the operator can save on production time while maximizing tool life and at the same time producing a quality end product.
