Thanks for you reply,
Two immediate thoughts:
isn't that the same issue for any servo ?
Yes and No, a servo when falling behind will usually have plenty in reserve so the drive can compensate and move the motor to where it should be. If it goes out with the following error set for it so if the drive cant get it to the correct position within the correct time/distance it will fault.
A stepper when its falling behind is because its overloaded so has no more to give so the drive cant give it more so the only option would be to fault it.
Interesting point re. the two axes - do people ever use rotary tables to get around using two axes for off axis cuts ? i.e. rotate piece to X or Y - cut - rotate again - cut - etc... Circles easy also - I guess arc's would have the issue of two axes (X or Y moves with rotary movement) - I have a rotary table and am keen for four axis
Many people use a rotary axis but not for doing circles, the axis should handle that no problem, if they dont then the motors are not up to it or the mechanics of the machine are too sloppy.
As for the benefits of the fastech - I was looking at the front page of that link I posted - stuff like this:
and so on...
marketing hoohah or ?
I have no idea what they can or cant do or whether its hype or not but what I can say is I dont think in a machining perspective it will be of benefit. A stepper is very accurate unless its overloaded and once overloaded its no use, so correct sized steppers and the problem is not there.
Also worth pointing out there are a lot of differences from one servo system to another so giving a general sweeping picture as above is just good marketing IMO.
Hood