Figure 6-68.  Closeup of head. Figure 6-70.  Second step in forming a stitch. Figure 6-69.  First step in forming a stitch. There are three types of feed mechanisms to move material  through the machines. The first and simplest is called a  “drop feed” machine. With this type of feed, a feed dog on  the bottom rises up to press the material against the presser  foot from the top and moves it along while the needle bar  complete revolutions to complete one stitch. The oscillating  models are generally slower in operation while the rotary  is the high-speed model. Aside from the larger, heavy-duty  machines, most new machines are rotary in operation.  [Figures 6-74 and 6-75] 6-19