Quote Originally Posted by GEOFFREY View Post
Surely one advantage with closed loop is that if the following error is set to a very small figure, the machine will just stop, and not perform any squiggles, rather than continue after a machining error? G.
Yes geoffrey that is true upto a point and actually how servos work. Lots people don't realise that a servo never actually is truely on the path but instead is continually off course and making tiny tiny course adjustments TRYING to get back on the path. Obviously these adjustments are so small they are not seen in normal use.
But if you set the parameters too high then you will be open to faults all the time. It's essentially a balance between accurecy and reliabilty.
Also it only faults AFTER it's got lost so still some damage is done, yes with high falling error setting you have limited it but still material you didn't want to lose has gone.!

Now don't get me wrong I'm not saying Servo's are Rubbish or not better than Steppers because they are in several ways. BUT not always in the ways people think and they certainly often put too much focus on the closed loop aspect when in real terms it offers very little over a properly Sized and setup stepper system. Esp at DIY level to Low end industrial use.