Power feeds attach to the ballscrews of milling machines, drilling machines, and other machine tools to provide an accurate, repeatable feed rate. They are designed to provide automated feed replacement for handwheels on manually-controlled machine tools.
By definition, handwheels are manually-operated devices that revolve around an axis and are used to adjust machinery. The ballscrews to which power feeds attach are used to convert rotary motion or torque into thrust or linear motion. The ends of the ballscrews provide the points for attachment for these electrically-controlled devices. In turn, the power feeds provide a smooth, repeatable, automated motion. Some power feeds are designed for specific makes and models of equipment, while others are designed for use with milling machines and drilling machines from multiple manufacturers. Electrical power feeds carry electrical specifications as well as listings for speed range, torque rating, bore size, and keyway size.
Most products are listed as 110-V, 50/60-Hz, 4.0-A electrical devices. Speed range is given in revolution per minute (rpm) while torque rating is specified in pounds per inch (lbs/in). Bore and keyway sizes are measured in inches (in) or fractions of inches, or in metric units of measure such as centimeters (cm) or millimeters (mm). In addition to torque rating, electrical power feeds may carry specifications for intermittent torque and continuous torque. Variable feed rate, gear reduction ratio (motor to screw shaft), approximate weight, and physical dimensions are also important to consider. Many electrical power feeds are equipped with features such as a rapid traverse, safety clutch, variable feed rate, pilot light, auto cut-off at the end of the cut, and electric limit switches. These products may also feature a full-wave SCR/DC motor and an electro-mechanical clutch that can reverse direction without coming to a complete stop. By limiting torque, these power feeds can protect gears from breaking. Power feeds with an electro-mechanical clutch and full-wave silicon-controlled rectifier (SCR) circuit also provide superior cutting at low speeds. Often, a job switch is used to permit incremental moves; the length of each move is adjusted by a speed-control setting. Power feeds with limit switches may have a fluid-protective cover and a control panel fluid-protective lip that can minimize coolant damage to control switches. Power feeds with helical gears are relatively quiet.