Nit-pick print quality question - just curious

[iras]

The repetition is 14/cm (calculated as 0.71mm/ridge) My X and Y axises are both belt driven.

If I put my finger on the print head as it moves across the X axis, I can feel it "step" across, even when visually it appears to be moving smoothly and at a decent speed.

This leads me to believe that it is the stepper motion. For example, in order to move 50 mm, maybe it is moving in units of 0.71mm - perhaps Marlin is telling the stepper to move 0.71mm over and over again to achieve the 50mm.

Note that I have my stepper drivers (X in particular) adjusted to that they aren't supplying more current than they need, but yet enough so that there are no missed steps (print accuracy and repeatability are both good). Rods are greased so movement across them isn't impeded.

The more I think about it, the more I think I'm seeing the stepper microsteps. If so, what can I do to smooth things out? Or is this just the nature of the beast?

Thanks.

[printbus]

...The more I think about it, the more I think I'm seeing the stepper microsteps.

Unlikely. Assuming you have a 20 tooth pulley on the X and Y motors, the Marlin DEFAULT_AXIS_STEPS_PER_UNIT setting for X and Y should be 80 steps per mm. This means each microstep would give you 1/80 or 0.0125mm linear movement per microstep. Your 0.71mm pattern interval is in the neighborhood of 57 microsteps, again, depending on what you have for a belt pulley on the X and Y motors, and DEFAULT_AXIS_STEPS_PER_UNIT values in Marlin.

Anyone can jump in with different opinions, but I'm not aware of anything in Marlin that would cause it to pause at an interval like this.

BTW - if the issue is appearing on both X and Y, there could be an issue on the extruder that is affecting the ability of the extrusion to flow smoothly, and this could lead to a pattern like what you have. Perhaps trying another layer thickness or something else that would cause the extrusion volume per distance to change would confirm or rule that out. EDIT: Although having an extruder issue that causes the pattern to be consistent in the z-axis would be unusual.

[lakester]

... it might be interesting to know what happens if you change the print speed.... Is the "ripple" frequency invariant wrt tool speed?

[Roxy]

The repetition is 14/cm (calculated as 0.71mm/ridge) My X and Y axises are both belt driven.
This leads me to believe that it is the stepper motion. For example, in order to move 50 mm, maybe it is moving in units of 0.71mm - perhaps Marlin is telling the stepper to move 0.71mm over and over again to achieve the 50mm.

This might not be drive belt related. It might just be the extruder motor doing steps and you are seeing it the print. You could over extrude by a small amount and see what happens. I would expect the frequency of the ripples to increase, but for them to be harder to see because they will 'smear' together if this is the case.