Following some further testing I am starting to form a “new” hypothesis that I would like to sound board with the group.
I think it is group member @xchrisd that once said, in another post on the forum, if you don’t know what is going on “…just watch your print to see what it does as it prints…” so this is what I did and after which I noted something “small” and I started looking at the Gcode at these “small” instances, and from this my question - What is the minimum or smallest G1 E value the printer can execute?
Using the same Seam test file posted in my original post, I watched the print. I noticed that in between where the cylinders are linked the printer appears to just move there and then do nothing and then moving to another spot, this happens (on my print) a couple of times before the each of the seams with the issue. So, I moved to the GCode and I think I found the below:
Using a random layer of 21, because it has both an inside and outside seam with issues
Figure 1: Layer 21 of test file at 0.16mm layer height and strange seam artefacts
Originally I just looked at the GCode at the location of where the seam was and what was following the seam however, as can be seen at the bottom of Figure 2 (the GCode section) there is nothing “strange” there and the “E” values was similar to areas without issues. So I started looking at the GCode leading up to the seam, and I refer you to Figure 2 as a picture speaks a thousand words.
Figure 2: Locations of very minimal printing before seam
As mentioned earlier the printer, when viewed, seemed to “do nothing” at point 1, then move to point 2 and do nothing again, before moving to point 3 and then under extruding. Viewing the GCode, the inner wall print (yellow) is so small that it is not even indicated at points 1 and 2, and only the retraction (purple/pink) and de-retractions (light blue) are shown. Viewing the “Printing at Point 1” and “Printing at Point 2” portions of the GCode, it can be seen that the “E” values are a order of magnitude smaller than “normal” printing (GCode shown in Figure 2):
- Point 1 E-values: 0.00094 - 0.00163
- Point 2 E-values: 0.00096 - 0.00167
- Outer wall E-values: >0.02
Noting this, and this is where my hypothesis commences, if these E-values are too small for the printer to handle (potentially limited to the single extruder), the extruder will ignore these “print” instructions and instead do nothing (in my mind, the Stepper motor does not have a step small enough for this instruction).
IF the above is true then the sequence in Figure 2 above can be summarised as:
- Do nothing at point 1
- Retract 1mm and move to point 2
- Push out 1mm at point 2
- Do nothing at point 2
- Retract 1mm and move to point 3
- Push out 1mm at point 3
- Start printing at point 3
However as the printer is using “Relative E values” potentially the controller is not seeing the motor as doing nothing, but rather sees it as:
- Extrude 0.0042mm at point 1 (the summation of previously “ignored” E-values)
- Retract 1mm and move to point 2
- Push out 1mm at point 2
- Extrude 0.0043mm at point 2
- Retract 1mm and move to point 3
- Push out 1mm at point 3
- Start printing at point 3
In the example above, the difference between the controller and what really happened at the extruder is approx. 0.0085mm. And my theory is that this is the “under extrusion” witnessed following the seam at only certain, or specific instances, but not all as it is dependent on the amount of “too small to print” steps leading up to the seam and is potentially aggravated by the retractions and de-retraction.
It is difficult to show the image and the GCode for the seam at the inner wall of the Cylinder (not the inner wall of the print) but the “same” occurrence happens here, refer to Figure 3, but in this instance, there are 4 instances of the same sequence happening rather than just 2 as in the example above before it starts printing the wall on the inside of the cylinder at point 5:
Figure 5: Sequence of events before inner seam with problems.
GCode for the above sequence below:
;WIPE_START
G1 X193.956 Y179.229 E-.45
;WIPE_END
G1 E-.55 F2700
G1 X159.866 Y178.591 F6000
G1 E1 F3600
;WIDTH:0.37962
G1 X159.801 Y178.629 E.00172
G1 X159.866 Y178.666 E.00172
G1 X159.887 Y178.629 E.00099
;WIPE_START
G1 X159.866 Y178.666 E-.03237
G1 X159.801 Y178.629 E-.05607
G1 X159.866 Y178.591 E-.05607
;WIPE_END
G1 E-.8555 F2700
G1 X124.956 Y177.446 F6000
G1 E1 F3600
;WIDTH:0.519692
G1 X124.896 Y177.446 E.00196
G1 X124.865 Y177.499 E.00196
G1 X124.896 Y177.551 E.00196
G1 X124.956 Y177.551 E.00196
G1 X124.987 Y177.499 E.00196
;WIPE_START
G1 X124.956 Y177.551 E-.0455
G1 X124.896 Y177.551 E-.0455
G1 X124.865 Y177.499 E-.0455
G1 X124.874 Y177.483 E-.0135
;WIPE_END
G1 E-.85 F2700
G1 X124.959 Y172.424 F6000
G1 E1 F3600
;WIDTH:0.527654
G1 X124.898 Y172.424 E.00202
G1 X124.867 Y172.478 E.00202
G1 X124.898 Y172.531 E.00202
G1 X124.959 Y172.531 E.00202
G1 X124.99 Y172.478 E.00202
;WIPE_START
G1 X124.959 Y172.531 E-.04625
G1 X124.898 Y172.531 E-.04625
G1 X124.867 Y172.478 E-.04625
G1 X124.874 Y172.465 E-.01126
;WIPE_END
G1 E-.85 F2700
G1 X159.87 Y171.331 F6000
G1 E1 F3600
;WIDTH:0.3745
G1 X159.806 Y171.368 E.00167
G1 X159.87 Y171.405 E.00167
G1 X159.891 Y171.368 E.00096
;WIPE_START
G1 X159.87 Y171.405 E-.03189
G1 X159.806 Y171.368 E-.05523
G1 X159.87 Y171.331 E-.05523
;WIPE_END
G1 E-.85764 F2700
G1 X142.361 Y191.907 F6000
G1 E1 F3600
M204 P500
;TYPE:Outer wall
;WIDTH:0.419999
G1 F3000
G1 X141.527 Y191.88 E.02141
So again, my question: What is the “smallest” E-value that can be printed?
I am however not experienced enough to know if there is merit to this discussion and as such, reaching out to the more experienced/knowledgeable members for comments?
Thank you in advance.