RE: [CAD_CAM_EDM_DRO] So many choices - Best way to make Sherline CNC

Ken:

In theory, the servo system would be more accurate than the stepper system
simply because the servo uses positional feedback to determine the location
of the table.

But, theory and practice are sometimes two different things. In order to
obtain the accuracy that the servo is capable of, you'd have to figure out a
good way of mounting a grating and sensor on each of the three axes in order
to actually determine the position of the table. Simply mounting a shaft
encoder to the lead screw would provide no additional accuracy because it
doesn't take any backlash into account, and the Sherlines are specified as
having from 2-5 mils of backlash.

So, the major advantages that the servo has over the stepper motor are two:

First, positional feedback ensures that the servo actually moves the
leadscrew to the correct position; a stepper motor can drop steps and not
tell you about it. If you select your steppers properly for the forces that
they will have to oppose, you shouldn't drop steps.

Second, the servo provides a better torque vs speed curve than the stepper.
This means that you can move the tables faster with the servo than with the
stepper.

As I see it, the major disadvantage of the servo to the stepper is cost.
Stepper motors and their drivers are typically cheaper than the servo
system.

-- Carol & Jerry Jankura
Strongsville, Ohio
So many toys, so little time....
|
|I'm know that this has been asked over and over again but cannot find
|one with this twist. There are basically (as I understand it) 2
|options to convert a Sherline Mill to CNC. 1 would be to use stepper
|motors, and another (?) to use servo motors. My question is which is
|better and more accurate?