Fine adjustment mechanism for drawing compasses - has spring loaded sleeve around adjusting screw inside sleeve with nut

摘要

A pair of draughtsman's compasses has a coarse adjustment mechanism on one leg and a fine adjustment mechanism on the other leg. An adjusting bar (3) through the two legs passes through a trunnion (6) secured to one leg (2) by a pin (7). This has a threaded end (9) passing through a plastic nut (11) embedded in the end of a knurled adjusting knob (12). As the knob is rotated, the nut (11) pulls the adjusting bar through the trunnion, thus pulling the two legs together. This action is assisted by a split sleeve (8) resting at one end against a flange (17) on the adjusting bar, with a shoulder (19) resting against a flange (15) around the inside of the knob (12). This carries a spring (16) which opposes the adjustment. Another nut 10) on the threaded part acts as a stop to limit the adjustment.