Microstepping and accuracy

[telephone1652]

I'm curious about what level of microstepping folks are using. As I understand it, you lose some accuracy as the number of steps per rotation increases. This article talks about it:

There's also this lively discussion:

Has anyone actually observed a decrease in accuracy with an increase in #of microsteps?

[cncbasher]

microstepping is really to help with resonance of the motor , rather than resolution or accuracy

designing in the resolution of the mechanics of a design is a far better route , than trying to rely on electronics to hold a position between poles of a stepper , the pole with the most pull
will always win , as does gravity with your z axis , ( missed steps on your z never moves the axis up , always down ) . and a stepper can only really move 1.8 deg (or 0.9) , anything else is
an electronic workaround .

with steppers voltage gives you speed , current gives you torque , as the modern stepper drivers control current , then you can see where this is heading ..
hence the higher the microstepping the less torq you have available than say at 1/2 step or at most 1/4 step .

iv'e simplified it a bit here to make it easier to understand.
but if you can keep the stepper driver to no more than 1/4 micro stepping you'll find you can move far quicker and hit the spot every time
than trying to go to 16 or 32 microsteps , especially if you have mass to accelerate say on a gantry

steppers are very good at holding and moving to a position , so long as you have designed in the correct motor regarding mass etc

[PomeroyB]

A good rule of thumb is to make sure your layer height is a multiple of your steps per mm (Without any microstepping). This way, whenever you move a full layer, you can be sure that the shaft will align exactly with one of the magnets in your motor. You get all the benefits of microstepping (Less resonance, smoother motion), but you don't lose accuracy.

[PacManFan]

[telephone1652]

Thanks for the input, everyone.

I'm not entirely certain I'm understanding the layer height point. Won't I need microstepping to get down to very fine layers, say 20 um?

[PomeroyB]

You could do that, but you may run into issues with the shaft trying to hold a position between two poles.

Basically, if you want repeatable fine movements (Like 20um), you're better off implementing gearing or using different belts/pulleys to increase your steps per mm.

That said, few people seem to adhere to these rules (My Uncia machine, for example, breaks this rule). Since I print at (a relatively large) .1mm layer height, it's not that big of a deal.

[telephone1652]

That makes sense, and thanks for the input.

At this stage, all the parts for my Z-axis are milled and assembled, so I'll have to keep that in mind for the next design.

Once I get my hands on some better measuring tools I'll post my results. Right now with 1/8 microstepping, 800 steps/unit, and 10um steps things seem fairly dialed in.