An apparatus comprises a body and a shaft assembly. The shaft assembly is in communication with the body and comprises an end effector, first cam gear, second cam gear, and a lock bar. The end effector has an articulation joint. The first cam gear is rotatably positioned within the shaft assembly. The second cam gear is in communication with the end effector at the articulation joint. The lock bar is distally biased to lock against the second cam gear. The first cam gear is rotatable through a first range of motion to unlock the lock bar relative to the second cam gear. The first cam gear is rotatable through a second range of motion to rotate the end effector at the articulation joint.
