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I just made a remix of that mod to have a more rigid chassis for Z axis.

While the parts are a little too heavy to my taste, I did import the STL to FreeCAD and made some adjustments before printing. I noticed weird defects on the layers in the range of a hole. It seems that all the layers belonging to a hole have a small offset, and sometimes the part is literally sliced, like for the layer tangent to the bigger hole (8 mm diameter) or the small hole (3 mm) on the left of the picture where I can see through the part (!)

enter image description here

That part was printed without any support on my CR-X and I noticed that the mirrored part printed in a different position has the same defects on the same layers, so I doubt if can be an issue with the hardware. The slicer is Cura 4.6.1. It takes 6 hours, so I did not watched it and cannot tell if the print is making a pause at some points (I suspected the minimal time for a layer setting for the smallest part, but it is probably not the case for the biggest hole).

Do you know where these weaks could come from?


Here is some additional info to help for the diagnosis:

  • one proposed explanation is clogging, but i think it is not the case for the following reasons:
    • I replaced the stock spool holders by ball bearing mounted holders from this design (no issue to print it) and the general setup (after the chassis mod - so is was less rigid to build the part of my question) is now this one, the parts mentioned in my initial post being the ones used to mount the threaded rods so the resistance to extruder steppers is minimal CR-X
    • as told, I printed for the chassis mod 2 x 2 parts from 2 initial designs, and the mirrored part for left/right sides, the defects are quite identical (same Z layer) in each pair of parts, while the mirrored part was turned is a different rotated position around Z axis, but in different layers between each pair (not the same distance from bed). Here is an example of the top mounts for threaded rods (and I remark there is a slice in the middle of a hole, not tangent to it) enter image description here
    • I managed to print additional pieces without issue and with satisfactory aspect and no defect at all e.g a improved part for my coffee machine (right of picture) 110 mm diameter / 12.5 mm height enter image description here

The black parts were printed using basic PLA, 0.15 mm per layer, 190 (or 200 ?) °C for nozzle / 60 °C for bed, 60 mm/s with 8 mm long & 70 mm/s for retraction (and possible Z hop while retracted and during layer change). I am unsure because I did not keep this Cura project but these are my usual settings for now. I have only the machine for a few weeks.

Also: I have checked the belts but they seem neither too loose nor too tighten, while it is difficult to get an accurate idea of the tension. I would rather suspect a Z axis problem (for the slices), but it is driven by dual square threaded rods.

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  • $\begingroup$ This is typical behavior for low end budget printers, I've seen seen before. Higher end printers generally have a more rigid frame which improves the accuracy of laying down filament. You frequently see this happening where the hotend needs to suddenly change in direction (e.g. the holes), could be high acceleration or jerk settings or just plain high printing speed. For the missing filament, you might be facing clogging or filament that is entangled on the spool. Please add more information on settings and setup of the spool. $\endgroup$ – 0scar Jun 2 '20 at 21:54
  • $\begingroup$ @0scar: I don't find it typical. Almost surely there's play in the belts whereby the final position ends up depending on the direction of the move leading up to it. Tightening them should fix it fully. $\endgroup$ – R.. GitHub STOP HELPING ICE Jun 4 '20 at 22:33
  • $\begingroup$ @0scar: thanks for your attention, I am not sure of what info you want actually so i have edited my question add more context and settings $\endgroup$ – Seki Jun 4 '20 at 23:37
  • $\begingroup$ @R..GitHubSTOPHELPINGICE: the belts seem ok, no too loose, not too tighten but it is difficult to be precise, and to it seems weird that a whole range of layers would have a reproductible offset only on the interval of a hole $\endgroup$ – Seki Jun 4 '20 at 23:45
  • $\begingroup$ You might want to test printing without the heavy spools on top of the frame, that is usually not a good idea (on the other hand you did strengthen/rigidized the frame). Also, 0.15 mm is probably not a native stepper revolution size, try 0.16 or 0.2 mm. $\endgroup$ – 0scar Jun 5 '20 at 9:43

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