DEVICE FOR LOCKING A ROTATABLE DRAWING HEAD

摘要

A single operating lever control for locking and unlocking a rotatable head on a drafting machine wherein a lock pawl is released from engagement with the teeth of a ratchet disc. A thumb operated lever extends along the side of the conventional hand knob and may be operated in one of two ways. Upon direct inward movement, the pawl is released only so long as the thumb lever is held. In the other mode of operation, the thumb lever is locked so that the lock pawl is retained out of ratchet disc engagement.