They are rolled, but they may be what is in your budget of a couple of hundred for the 3 axis. I suspect that percission ground ball screws will be very expensive.
As you may know, the rolled ball screws are about .004 accuracy per foot. If you are milling a peice which 3 inches in length, the ballscrew (assuming you use preloaded ballnuts set to give zero backlash) could contribute .001 inch error and still be in spec.
Now, the machine using the rolled ball screws still would have excellent repeatability.
I guess you will need to look at your requirements and determine how much accuracy you need and that will drive how much you will need to budget.
Ron |