A bale binding mechanism is configured to secure a strand of binding material around a bale of severed crop material. The bale binding mechanism includes a chassis, a knotter head assembly, and a captive lock. The knotter head assembly is operable to form at least one knot in the strand of binding material. The knotter head assembly includes a knotter head frame swingably mounted relative to the chassis and rotatable into and out of an operating position where the knotter head assembly can form the at least one knot. The captive lock is shiftably supported by one of the chassis and the knotter head frame. The captive lock is removably engaged with the other one of the chassis and the knotter head frame to secure the knotter head assembly in the operating position, with the captive lock being releasable to permit rotation of the knotter head assembly out of the operating position.