Speeds and feeds are integral components of any machining process. Today we are going to go in depth on how both cutting speeds, spindle speeds and feed rates affect the manufacturing process. Cutting speed is simple; it is the rate a work piece moves past the cutting edge of a tool. This is measured in units of distance per unit of time, normally surface feet per minute (sfm). Cutting speeds are directly affected on a few key factors: the material being cut, the material of the cutter, and the expected life of the cutter. The example chart below, for the turning process, is calculating cutting speeds with a feed rate of the mini lathe (0.004/rev.), a depth of cut of 0.040, and a tool life of 180 minutes. This information, as well as more information on cutting speeds can be found at, http://littlemachineshop.com/reference/cuttingspeeds.php.
Once cutting speed is achieved we can then calculate the proper spindle speeds. Spindle speeds are important for a number of reasons. Improper spindle speeds can cause premature tool wear, tool chatter, breakages, and potentially unsafe conditions. Proper spindle speeds can prolong tool life as well as improve the quality of surface finish. Once spindle speed is calculated, feed rate is the next factor we need to consider when machining.
Feed rate is the velocity at which the cutter is fed. This is usually measured in units of distance per revolution in turning and boring and is expressed in units of distance per time in milling. For both processes, feed rate is dependent on a number of variables: tool type, desired surface finish, power at the spindle, rigidity of machine and tooling setup, and strength and characteristics of the work piece. One major factor to consider when deciding feed rate is the number of teeth doing the cutting. The more cutting heads a tool has, the high feed rate allowed.