A pencil head for automatic pencil drawing is provided with an up-and-down moving mechanism for one of pencil leads held on a periphery of a holding turret and a mounting mechanism for the holding turret, the up-and-down moving mechanism comprising a spring for raising a resilient member grasping the...http://www.google.co.uk/patents/US4423428?utm_source=gb-gplus-sharePatent US4423428 - Pencil head for automatic drawing instrument
