My very large, very tall print was going well on my A1 mini until 75% up the tall print when there was a pronounced layer shift that was worse on the front right corner yet OK on the back left corner. There was another pronounced layer shift at ~95%.
The magnetic build plate shifted! I’ve never had this happen before.
What can I do about it?
The print is firmly adhered to the smooth PEI plate even now that it’s cold. I could switch to the textured plate but then the whole print would have shifted.
Obviously there were strong lateral forces which I have to prevent. Change from grid infill to gyroid?
I would print alignment tabs to hold the bed in place, but these don’t exist and if I did design them, I can’t think of a way to attach them to the front.
I notice the “shifts” are high up in the Z direction. Could this be caused by the cantilevered arm sagging a bit?
Though to push it like that, rotating the print and bed in a clockwise direction, it would have to be pushing forward and/or to the left at the front right corner. Here the extruder is close to the start of the arm, so any small sag would be minimized.
On the curved parts at the top of the design the printer has to print pretty large overhangs. These can curl up during printing and hit the nozzle in the next pass, shifting the bed.
You might want to look at cooling or variable layer hight to reduce the overhang on the curved part.
Hmm, good idea. I was thinking the design had something to do with it. The print consists of little islands - one island is printed, then the nozzle moves along the wall, printing the next island and so on, with a Z hop each time. The nozzle is moving along at high speed in midair until it hits the next island. This may bump the print and shove the bed a bit each time. Reduce travel speed?
It worked well enough at lower heights, at higher heights there was a lever effect which amplified these forces.
And there’s the bridging as you mentioned. This wasn’t working perfectly anyway, if the print would have succeeded there were some sagging filament loops which I would have had to trim off with a knife.
The print’s too tall anyway. I’ll try again at 50% Z scale. That should reduce the “lever” effect. It may disrupt the geometry though.
Maybe its the photos but the plate appears to of moved in two directions ( left and forward ) but the actual print only appears to of moved to the right ,
That disrupts the voronoi geometry so much the arches become horizontal overhangs, giving me a floating cantilever warning. I think I’ll give up on this. I’m not using internal supports.
I think it moved twice, the bed plate rotated clockwise each time.
You can see the right wall is still parallel to the bed edge at the end, while the lower parts of the print remain parallel to the plate edge at the time they were printed.
Oh that’s interesting. Yes a very large, very well adhered print like this will want to pull at the bed as it contracts.
I do note that the print is still very well adhered now that the bed is cold and perfectly flat. The plate’s not warped now that the print has fully cooled.
I’m printing right now so I can’t look.
I did just watch 3 videos on Bambu Wiki & didn’t see any print of the magnetic sheet under the plate…but I noticed the letter “N” in your pic.
Also, this looks black & not brown.
I’m using a smooth PEI plate, which is black. That “N” is definitely the magnetic surface, the full text reads “CAUTION”. It is brown, but the lighting is poor.
The plate did shift, you can see the angled line to the left of the “N”.
At any rate, I worked around it. It was surprising though.
