So if you have a pocket that is 2.997" long and it is supposed to be 3.000" long, you can detect that VISUALLY?
Why is it that everyone has to pick this out. I said theoretical exactly because I know it isn't real. It was only to depict how the machine is set up.I suggest you spend a lot of time reading and researching how stepper motors really respond, in the real world, where things like friction, stiction, inertia, and other physical factors interfere with the "theoretical". Learn how a real stepper motor responds to micro-stepping, and you'll realize even talking about 0.0001" is ridiculous. Factor in the real-world characteristics of the machines being talked about here, and it becomes downright ludicrous. Learn that micro-stepping has virtually nothing to do with increasing resolution, but is, rather, used primarily to reduce resonance at low-to-moderate speeds, and that many drivers automatically switch to full-step mode at higher step rates.
I see no contradiction at all. What is acceptable is dependent on what you are making. A 0.005" detection error for the types of parts I usually make would mean that a fault at 0.005" would likely mean I would be able to change a tool or whatever, re-home, and then save the part. 0.005" would also insure that no further damage is done to machine, fixtures, etc.And, if I follow your argument, I am wrong to suggest that I can tell if my open-loop machine is losing steps, because I can't possibly detect a 0.0001" position error, but you are going to allow a 0.005" position error on your machine before you trip a fault? Do you see a logical contradiction there? How is a 0.005" position loss acceptable, when a 0.0001" loss is not? How do you suppose you are likely to ever achieve a 0.005" position loss without stalling the motor? The fact is, with steppers, once you've lost a single step while moving at anything other than extremely low speed, the motor is almost guaranteed to stall. THAT is easily detected without encoders.
I never said that a machine with steppers without encoders wouldn't work or that it is necessary, I only said that it is "not totally useless"Finally, consider this: If simply adding inexpensive encoders to a stepper motor (and decent optical encoders can be bought for a few $ now) has such wonderful, wide-ranging benefits, why is it so very, very rarely done, even in the industrial world, where cost is not nearly as much of an issue as it is here? A great many extremely high-precision machines use open-loop steppers, with virtually 100% reliability.