Zigzag Stitch Mechanism

The lock-stitch machine already published sews a straight line, and a straight line of thread cannot stretch - which is why early machines could not sew knitted cloth, finish a raw edge, or work a buttonhole. The next rung is a mechanism that swings the needle bar sideways between stitches, driven by a cam turning with the main shaft. **US 1,466,150**, "Zigzag mechanism for sewing machines", Ralph M. Sharaf, filed 2. April 1917, granted 28. August 1923: a cam-driven vibration of the needle bar while the machine stitches, with the throw adjustable. Domestic zigzag machines followed in the 1950s. **You build the motion in wood** - a cam, a follower and a pen drawing the needle's path - then sew both stitches on jersey and pull them until something gives.