What drives sewing machines?

Sewing Machine drive systems

Of the thousands of brands & models of sewing machines, there are a wide variety of different mechanical systems used, to transfer power from the motor, or power source, to the main driveline of the sewing machine, to make the needle go up & down. The energy source can run from hand driven, to pedal & treadle driven, electric, steam driven (in old factories),

While any of these drive systems can be broken, damaged, or worn out, and have that affect the speed and strength of the sewing machine, each system has it's positive points, and negative points. Some machines use 2 systems, one for transferring power from the motor to the machine's main components, another to synchronize the top of the machine, with the bottom of the machine.

Gear driven - Singer 101, 201-2, & other Singer potted motor machines, or worm gear driven from a motor under the machine bed, like the Singer 301, 400, & 500 series. Gears can be steel, or various types of "plastic", fiberglass, resin, or other materials, and can be helical gears, spiral gears, or other configurations. While some "plastic" gears are very hard & strong, and don't break easily, with the business idea of "built in obsolescence" as a key to keeping a company open for business, because parts break, and customers then have to go buy a new machine, or at least take their old one in for repairs, so they can be talked into trading the old machine for a new one, poor quality plastic gears became the norm, in most home sewing machines. Most people aren't aware that this started before the 1980's, and with some manufacturer's, the 1960's.

Singer 500 Rocketeer motor with spiral gear

Steel gears commonly found on most vintage sewing machines, this is Singer 500 Rocketeer
Beginning after the Singer Touch 'n Sew 600, Singer switched to plastic gears, but some lucky buyers were able
to get steel gears in a few individual machines, before the factory it was built in, ran out of steel gears.

Gear driven/cleated belt driven- Fiberglass belting, cotton belting, or other types of fiber woven belting, with metal cleats, that look like heavy steel staples, evenly spaced, grab the gears in the top & bottom of the sewing machine, like German made vintage home & Industrial Pfaff sewing machines, like the 130, 230, 260, 360, 332. The Singer 206, 306, 319, and some of the industrials, use a cleated belt to gears, system. Some machines use both the cleated timing belt, to transfer power from the top of the machine, to the bottom of the machine, and a rubber pulley to drive the machine through the handwheel, like the Elna Supermatics.

Notice the metal cleated belt on the top inside the right side of vintage Pfaff machine, with the upper embroidery mechanism removed.  Note flat hard resin helical gear on back wall of machine.

Belt driven

Leather treadle belt on Singer 127 Vibrating Shuttle sewing machine

Treadle machines, and machines with a motor on the back of the machine, or even underneath the table (like industrial clutch motors). In old factories, huge belts ran rows of sewing machines on long tables, running off steam engines, mill style waterwheel power, or electric motors & rubber belts. Some belts are rubber, others are leather, some can be made of other fibers & textiles, even rope, or in inventive cases, many people have discovered that various special types of long springs can be used as a treadle belt for a sewing machine!

Be aware that the shape of your pulleys & make sure the belt you put on your machine is appropriate for the shape of the pulley grooves, for best transfer of power. Some belts, when cut on a cross section, are literally V shaped, and called a V belt, similar to those used in some cars, others are simply round, some are stretchy, some actually are a type of timing belt, and have teeth carved or shaped into them, to mate up with the gears in the top & bottom of the sewing machine, while others have kind of a  zigzag shape, so they wrap more firmly against the pulleys, in the curves.

Friction pulley driven 
Rubber friction pulley, works on a similar principle to the bobbin winding tire, but some friction pulleys feel more like a sanding or buffing bit, with something similar to sandstone pulley, or a metal texturized pulley, the methods & parts vary, by manufacturer. Old White & Kenmore machines manufactured by White, as well as National, often have friction pulleys,  but my favorites are the Elna sewing machines, with the rubber friction pulleys. Just remember that a rubber friction pulley, if left pressed against the machine for too long, without use, will develop a flat spot, which will make it run harder, noisier, and not as smoothly.

Close up of motor pulley in Elna Supermatic

Elna Supermatic note the cast aluminum handwheel, the rubber pulley rubs against the rim inside the handwheel, driving the machine.

Chain driven- Early Kenmore's made by the automotive industry, have a chain driven system. I am not as familiar with this system, so feel free to share information, if you like, in comments! Because I have tumors in my spinal cord, & keep having to have back surgery, lifting heavy machines just isn't something I can do, so I have given away some machines, which I knew I wouldn't be able to get around to fixing up, so I gifted this machine to another sewing machine enthusiast.