Cam Gear - Stitch Formation
For over a century, home sewing machines only did straight stitch sewing, but in 1952 zig zag machines came home. To form zig zag stitches a special gear was designed with bumps and ridges on its edge. This gear was connected to the upper drive shaft with another set of gears, and a lever (tracking lever or follower) rubs up against the edge of the cam bouncing back and forth. This lever was connected by a long lever to the needle bar controlling its movement.