I'm using the new Elegoo Neptune 4 Pro printer. I have the issue with both Cura and PrusaSlicer alike (I'm a Cura user).
The issue is simple, instead of printing a perfect circle, the final print will have a diameter range of around 0.3 mm. For example, if I print a 15 mm diameter cylinder, the longest diameter will be 15 mm but the shortest will be 14.7 mm.
I measured these with my caliper and I simply turned the cylinder around in the calipers; the cylinder will push up against the calipers as it reaches the thickest part of the cylinder and then come down as it goes to the thinner part.
It's not visible to the eye; it looks like a very nice and perfectly round cylinder. But I can feel it with the calipers. The height is dead on 25 mm as designed.
However, I don't get this result from the holes inside that same print. The holes are perfect circles and measure the same diameter roughly no matter what angle I measure them (at least I believe so, measuring the holes can be a bit tougher).
Calipers are accurate and go to two decimal places for mm.
- Tightening up the belts (a lot - caused the deviation to go from 14.7-15 mm to 14.53-14.8 mm, still roughly a 0.2-0.3 mm difference)
- Bed leveling
- Vase Mode
- Arc Welder (even though it technically shouldn't do anything)
- Axes calibration
I remeasured and found that the thickest part of every cylinder is not directly on the Y-axis, instead, it's diagonal. The bottom right and top left of the cylinder is the thickest portion while every other angle is roughly the same.
I found the same was true for the cube I made. Measuring from the bottom right to the top left resulted in 26 mm, but the bottom left to top right resulted in 25.67 mm.
Calibrated the the Y-axis (the only one that was off), issue persists. Again, this 0.3 mm deviation exists in the cubes printed as well, and always diagonally. Bottom Right to Top Left is always about 0.3 mm larger than Bottom Left to Top Right. Looked at an old calibration cube I made with my Ender 3V2 previously and the same measurements were only off by about 0.03 mm.
This is very strange, I think I may simply return this printer for a replacement.. I have no idea where to begin investigating this issue.
I took some measurements. I found that the right and left sides of the printer (which are separate pieces of aluminum) were roughly 0.2-0.3mm in difference from their distance to the aluminum center piece.
Now, without taking the entire printer apart, I can't say for certain that this measurement even matters, its possible that things aren't attached the way they seem from the outside.
However, the measurement perfectly aligns with the error margin on the prints. It also correlates to the X/Y axis misalignment, as the measurement indicates the
bed X-Axis is slightly tiled up on the right side by 0.2-0.3 mm. Had it indicated it was tilted up on the left side, the print errors wouldn't have made sense as the diameter would have increased/decreased on the wrong diagonals.
They agreed to a replacement after I sent pictures of the inconsistent diameter and measurements on the printer itself. I will update on if the issue is gone on the new printer once I have it.