Apparatus and method for locating the neutral bending plane of an elongated flexible shaft, typically a golf club shaft, by mounting one end portion of the shaft in a clamping mechanism having a rotatable clamp member that permits the shaft to turn about its longitudinal axis while being driven through a motion simulating a golf swing, with sufficient speed to cause the inertial loading of the shaft by its own mass, enhanced by a head weight, to turn the clamp member and the shaft into alignment with the path of movement of the shaft during the simulated swing. A brake fixes the shaft in this position during the swinging motion. A first embodiment uses a rotary motor to rotate the shaft in a radially projecting position about a stationary axis, with a clamping mechanism and brake mechanism on a base plate mounted on the motor shaft. A second embodiment mounts the clamping and brake mechanisms on a robotic golf-strokes machine to move along an arcuate path, and a third embodiment mounts the clamping and brake mechanisms for movement along a linear path, and a fourth mounts the clamping and brake mechanisms in a hand held mechanism to move along the swing path of the intended user.