Measuring and managing drawbar forces

Considerable effort has been devoted to the computation and measurement of the static stiffness, drawbar force, dynamic stiffness, accuracy, repeatability, torque capacity and maximum speeds of various toolholder/spindle interfaces. The spindle/toolholder interface provides stiffness and damping, and the conditions of the interface affect both parameters. Increasing the drawbar force increases the static stiffness, which is good, but it reduces the damping, which is bad. The increased stiffness resulting from the increased drawbar force is overpowered by the loss of damping. If the drawbar force were too low, the toolholder could wallow in the spindle taper, and accuracy and fretting corrosion could become issues. Generally, the drawbar force is not easily changed intentionally by an end user. Ensuring repeatable cutting performance from the machine tool means ensuring repeatable drawbar force. Several manufacturers offer drawbar dynamometers, the instrument used to measure drawbar force.