Sorry I haven't posted in a while , been real busy at work. I have been studying the difference between stepper and servo. I was real lost on the servo stuff till I ran across this site
http://www.vexrobotics.com/vex-robotics-optical-shaft-encoder-kit.shtml I have some real nice Pittman gear motors and wanted to use them and was lost in optical readers to make them work. This site has some optical encoders very cheep to play with $20 dollars. The micro controller is reasonable too. there is lots of info if you get lost and has the codes to make everything work. you can use AC or Dc motors with these. Surprising en ought there quit good quality for hobbyist. I'm posting a pic of the Lath and the cabinet I made to put it in. Good luck with your projects and have fun. to answer your question about the difference between the servo and stepper the servo will run at higher speed feed rates , the stepper has a drop off in speed at the higher RPMs. the stepper are designed for low speed applications and feed rates but have more power than a servo at low speeds. you have to remember that the servo has one more part the optical reader and the stepper fits in a smaller space and does not have the problems to adapt the O-reader. as for function I'm still learning what the two can do. sorry I'll have to resize the pic before I upload it.