Nit-pick print quality question - just curious

[iras]

This is a question more from curiosity than anything else.

I just printed a case for a Sainsmart oscilloscope board. The case came out perfectly, but I noticed that the sides have ripples in them (not this just print, but this one does show it more than others).

At first I thought it might be some artifact from the extruder hot-end. But looking more closely, all of the ripples are lined up from layer to layer. The side shown in the picture was printed with the head moving left to right - layers are horizontal:





Now I'm wondering if these ripples are actually there because the stepper motion isn't actually continuous, but a lot of micro-steps. That would explain why they're lined up. Maybe what I'm seeing as a smooth motion from left to right is actually step-microseconds pause-step-microseconds pause etc.

I'm not trying to change anything, just trying to learn about the process and curious.

[ZorAxe]

Is there any play in one of your axis? Maybe something is loose somewhere, so when the axis moves it's not moving 100% accurately

[iras]

Everything is tight and moves smoothly. It also does this on sides (Y-Axis too). Everything is printing cleanly and accurately. This has to be an artifact of something, just trying to figure out what.

[CaptainObvious]

That maybe resonance on the axes, if you are using belts think of them like the strings in a guitar, they'll tend to oscillate at a particular frequency. You could try to print a test piece and change the printing speed, or clip a small weight on the belt at some times and look if the pattern changes. If it doesn't then it's some other issue.

[printbus]

Measure the repetition interval. For a more accurate measurement, measure across say 10 intervals and divide the result by 10. Are you using belts or using threaded rods for the XY axis drive? Is there a correlation between the repetition interval and the belt tooth spacing or threaded rod pitch?

[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?

[morgue427]

Is it auto bed leveling? The ridge might be where it is moving in all 3axis at the same time making it go just a fraction on a mm out of line where the bed is high or low. Had a friend with an i3 see the same thing

[3DPBuser]

Get it figured out?