A mechanical sewing machine has no circuitry in it. The stitch patterns are formed by cams and followers. These cams or discs may be built in, insertable, or both. They have bumps on them, and as they turn, the followers are moved by the bumps and in turn move the needle to its proper position in the stitch as you sew.
The motor is AC (alternating current; see sewing machine motors). This is the same as your household current. The machine may have a rheostat or electronic foot control (see foot controls).
These are the vintage sewing machines or today’s lower-end offerings.
Mechanical sewing machines have no automatic needle stop, and they stop randomly in their cycle when you take your foot off the controller. When you stop, be sure to turn the handwheel toward you until the needle has barely started on its downward path. This will help prevent thread nests upon starting.