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0.200mm layer height, single wall

0.075mm layer height, 2walls, no infill

  • These lines exist on all prints, PLA, ABS.
  • They're 0.800mm apart [20T 2GT pulley, 1.8deg/step motor = 1 line/4 full-steps]
  • Start to disappear above 75mm/s but will still appear on slower axis when printing diagonal lines or curves
  • Custom built frame, cross bar (Ultimaker style) using linear rails
  • dual-motor(4 total on X-Y) + separate driver (1motor/driver)
  • Running Smoothieware on Smoothieboard 5X [A5984 drivers, 32 microstep]

Tried all these with no improvement: TL;DR problem is somewhere between drivers and motors

  • Switched to 6.625:1 geared extruder
  • Tried parallel, series, single coil on the 8 wires motor and 2 other different motors
  • Enable fast decay mode on A5984
  • Motor current from 0.5A to 1.8A
  • PLA temp from 170~200
  • Acceleration as low as 100mm/s2
  • **Changed 20T to 16T pulleys. The pattern scaled down proportional to the change in tooth count. Ruled out mechanical issues.
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  • $\begingroup$ Have you tried 1/16 micro steps? $\endgroup$ – 0scar Jan 20 '19 at 13:26
  • $\begingroup$ No, the drivers are soldered on-board and require tiny SMD resistor soldering to change microstepping, no jumper. THB6128 drivers and expansion board on the way. $\endgroup$ – INPUT_PULLUP Jan 20 '19 at 15:34
  • $\begingroup$ that looks like ghosting... $\endgroup$ – Trish Jan 20 '19 at 15:52
  • $\begingroup$ I've tried 100mm/s2 acceleration and it still appeared. Also they always appear perfectly vertical near curved edges. Definitely not ghosting. $\endgroup$ – INPUT_PULLUP Jan 21 '19 at 6:16
  • $\begingroup$ @0scar tried 1/16. Did not help. $\endgroup$ – INPUT_PULLUP Jan 21 '19 at 6:42
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The fact that these are all perfectly spaced, and don't mirror the edges of irregular prints, makes me think it's definitely not ghosting. That said, I can't see the Y direction on either print, just the X direction, so this all assumes it's only happening in one direction. One thing to think about: Your motors have typically 2 opposing coils, and they get activated by taking 4 steps: (North, off, South): N/o o/N S/o o/S If these are spaced out exactly 4 steps apart, that would imply that one of your coils is either underpowered or overpowered on the motor controlling that direction's movement. That would lead to your motor torque dipping and increasing, leading to slightly uneven print speed. This is 100% speculative and might be a goose chase since you've got 4 X/Y motors and it seems to happen in both the X and Y axis. The chances of having that many motors exhibit the same deficiency is astronomical.

That said, I've got little experience with multiple motors per axis. Another thing you might look into is whether the motors are fighting each other at all. If, for example, the motor-side pulley isn't aligned exactly the same way on both X motors, or the motors get out of sync with each other, because of the way the motor's holding torque falls as you get away from a full step position, you might find that one motor is holding the other back slightly, or pulling it forward towards the nearest full step. Again, this is all speculative, but it might be worth looking into. You can typically figure out the full step location by killing power to the machine and letting the motors settle into a full step on their own without the belts or other drive mechanisms attached. I'd unhook the belts, kill the power, get the motors settled (with a bit of a nudge if necessary), and then see if your belt perfectly settles into both pulleys in that location. You might find that the belt teeth don't quite line up on both pulleys, and the only way I can think of that would fix that specific problem is spinning the motor until it matches, or even physically relocating the motor closer or farther relative to the other on the same axis.

YMMV, best of luck.

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this is a great blog post explaining what i think im seeing, although im not entirely sure what im seeing in your photos. the short version is if your z-rods are threaded in an imperial unit, inches/fractions of inches, instead of metric, you get a repeating decimal value (think about converting 1/3 to decimal), which can lead to a rounding error depending on the chosen layer height. without knowing how exactly you built your machine its hard to say more but the post goes over a number of things i almost did wrong (like anti-wobble caps on top of the z rods for prusia i3s...)

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