Print is skewing
I printed one item a week or so ago, at 15% rectangular grid infill and it worked:
The bottom of the two photos includes the corners for my project. (Think of it as a pyramid shape made out of 1" square aluminum rods, so the bottom photo contains the bottom 4 corners and the capstone. It's the capstone I'm trying to print.)
I'm printing in PETG. I found, when doing tests, that the printed pieces were not strong enough, so I reprinted them at 50% infill, which took more than 3x as long to print. The denser corners printed just fine.
Then I prepared to print the denser capstone part. I had to edit the mesh to move some screw holes in it, which I did. Then I opened the STL in PrusaSlicer to slice it at 40%. Here's a screenshot of the sliced object:
It looks okay, and I don't see the issue I'm about to bring up.
This part, at 40%, takes 18-21 hours to print (for some reason, at this higher density, PrusaSlicer's estimate is off more than usual and OctoPrint, while printing, keeps changing the ETA.) Time is a factor because of the time required for test prints.
Here's the issue, and it's happened twice, at what looks like the same point, on both attempted prints:
This is the back of the print - but it's easier to see the issue here than from the front. The print shifted back a small amount at one layer. I can't find anything blocking my printbed so it doesn't have full movement, and have tested it manually. Same with the print head. (The skewing is on the Y axis - it's coming farther forward on the lower layers.) The first time I saw this, I thought, "I was down in the shop working on something and might have jarred the print table. So reprint it." I did and got the same issue and one more. The edges did not print well on the 2nd attempt:
I was in the room for the start of the print and saw nothing blocking the bed from moving all the way back as it was printing the first 2-3 layers. I also can't find a thing blocking the print bed from moving forward. I have checke FULL printer motion manually and there is no interference. I wondered if I could have misremembered the orientation of the part when I removed it from the print bed, so the skew might be on the X axis, not the Y. That'd make more sense to me that something might block the extruder moving along the X axis as it moved up, but I can't find anything interfering with X axis (or Z axis) movement, either.
RE: Print is skewing
More info:
Since things looked good in the slicer and I couldn't find anything obstructing the movement of any parts of the printer, I ran test prints. I started with a 1" square in the center of the print bed, about 3/4" high, which was above the level where things went wrong. It worked. So I did another test print with 5 of the square columns. I kept the one in the center and set each of the other 4 at the same location of the corners of the large piece I was trying to print. It printed okay. (I wondered if something could be happening at the edge of the range it was printing, but this printed fine, so I don't think it's how much the printer is moving.)
I resliced the STL, this time on my workshop computer. (I use Macs in my study and workshop, with the same version of PrusaSlicer on each one and the settings are synced.) This time the print shifted quite a bit to the left after the 1st layer. So that's 3 changes this time: 1) The shift was much larger, 2) It was not just on one axis, and 3) It was after the 1st layer, not after several layers.
Here's the last print attempt:
So something is making the print shift over, but it doesn't look like it's something interfering with the printer head or bed motion, but the slicer files look okay in the slicer.
I'm wondering if it could be the loss of data when I send the file to the printer from the slicer, like one command being lost, or something else forcing a wrong command. Other than that, I have no idea what it could be.
I will be trying some more troubleshooting. I'm going to try printing this file (already loaded into OctoPrint) and watch it to see what's going on. I'm not sure what good that'll do, since it's clear what's happening (the bed and print head just aren't moving the way they should). I think it might also help to actually upload a file instead of sending it directly to the printer from PrusaSlicer, in case errors are creeping in.
I'm also wondering if there could be something in the settings that might have somehow been changed, but I have no idea what that would be.