Constant Horsepower Applications

Constant horsepower applications require a constant force as radius changes. A lathe, for example, starts out with a certain diameter object. As the object is cut and shaped the diameter is reduced. The cutting force must remain constant. Another example of a constant horsepower application is a winder where radius increases as material is added to a roll and decreases as material is removed





Relationship of Speed, Torque, and Horsepower
Applications, such as lathes, that are driven in a continuous circular motion are sometimes referred to as spindle drives. Horsepower will remain constant in a spindle drive application. The surface speed in feet per minute (FPM) is equal to 2π times the radius (in feet) of the material times the speed in RPM. Surface speed will remain constant as the material is shaped and the radius reduced. Torque is equal to force times radius.
Horsepower is equal to torque times speed







The drive increases the speed (RPM) of the material as the radius is reduced. If the cutting tool has cut away half of the radius, for example, the RPM must double to maintain a constant surface speed (FPM). Reducing the radius by half will cause a corresponding reduction in torque. A doubling of speed (RPM) and a reduction of torque by half cause’s horsepower to remain constant.





A smaller radius requires less torque to turn. Because torque decreases with a smaller radius, motors operating a constant horsepower application can be run above base speed. A 60 Hz motor, for example, could be run at 90 Hz when the radius is at minimum. RPM must
a decrease in torque means horsepower will remain constant