Abstract: A spindle lock-up device for detachably locking a rotary spindle having a tool holder at its end to a non-rotatable support, such as the ram of a vertical boring machine, so that the spindle tool holder also may be used as a fixed tool holder for the ram, the device having a first spiroid gear member fixed to the ram, a second spiroid gear member surrounded by the first gear member and fixed to the spindle, and a third spiroid gear member surrounding said spindle and mounted for axial movement from a retracted to an extended position, the third gear member simultaneously engaging the first and second gear members when in the extended position to lock the spindle against rotation relative to the ram, the third gear member being moved to the extended position by a displaceable piston.