Originally Posted by willowbilly3
I have looked at a lot of big machines, never owned one really but it always looks like a problem to me. My brother in law bought a big industrial Juki sweat shop machine and quickly found out it was totally unsuitable for what he wanted, way too fast. I have been thinking a lot about a way to control the speed on one. A rheostat controlled motor is one choice but they never seem to have much power on slow. Another Idea I had would be a sort of transmission that had a rubber tire running on a spinning disc. The farther the tires moves out the disc, the faster the machine goes. I even have an old 29 series Singer I was thinking about experimenting on.
Why is everyone so afraid of actually learning how to use the sewing machine? When I first learned, there were no such things as servo motors so you either learned to slip the clutch motor or you couldn't sew with the machine.
Theoretically, a rheostatically controlled motor would work on a sewing machine because the slower you go, the more torque is produced. In practice, however it would not be very economical to do it that way. The motor would need to be a DC motor, because running an AC motor at slow speeds all the time would burn the motor up because it couldn't cool itself. They don't use DC motors because they are way more expensive than AC motors. The reason they used AC clutch motors on them in the first place is because, for a long time, it was the best and also the cheapest way to power the machine. Anyone who is any good at sewing can make a clutch motor do anything a servo can. The reason I switched to servos is because I hated listening to the sewing machine run when I wasn't pressing on the foot pedal, and the savings in electricity were so great.
The easiest way to slow down a sewing machine is to put a very small pulley on the motor, which will cut top speed by at least 1/2. If you also use a servo motor you can get the motor to absolutely creep. The servo is a constant torque device, so it has low end torque and is the simplest, and cheapest, way to get it all in one package.
You also need to practice with the machine. They don't just give you a driver's license when you're 16, you need driver's ed and experience too, just like anything else that is a learned skill.