Y-Axis Layer Shift On Mini...Rails and Bearings Are Smooth, Not The Issue. Help!  

RE: Y-Axis Layer Shift On Mini...Rails and Bearings Are Smooth, Not The Issue. Help!

I've never had layer shift on my mini, but i've seen it on the i3 that we have at work. On that machine we decided it was caused by having the wrong extrusion multiplier set in Prusaslicer. We think that the material was slightly over extruding and the nozzle was crashing into the oversize model and causing the stepper motor to miss a step or two. We haven't see this issue since we backed off the extrusion multiplier slightly.

RE: Y-Axis Layer Shift On Mini...Rails and Bearings Are Smooth, Not The Issue. Help!

Hey, 

Thanks for the response and insight. Did you find this failure to be intermittent, or something that happened all the time? Did you turn your extrusion multiplier up at some point to create the problem, or do you think it had to do with maybe a new material you switched to? 

Best,

T

RE: Y-Axis Layer Shift On Mini...Rails and Bearings Are Smooth, Not The Issue. Help!

Another possible source--if belts and grub screws are fine--is the nozzle crashing into infill. The default grid infill pattern has lines they intersect within a layer, which can cause filament pileups at the intersections. 

Another possible cause is filament warping at overhangs. 

RE: Y-Axis Layer Shift On Mini...Rails and Bearings Are Smooth, Not The Issue. Help!

The issue was intermittent. We only saw it maybe 3 times. We had never adjusted the extrusion multiplier prior to the issue. Reducing the extrusion multiplier to 0.98 seems to have fixed it. Because it only happened a few times, it's difficult to say if it was a material problem or a factor of the printer.

RE:

The Y-axis belt definitely deserves investigation, but unless it's actually sticking during self-movement, the steppers are most likely able to overcome any friction from potential misalignment. I worry that your belt may be too tight if everything spins/slides freely without the belt attached. Make sure to tension accordingly, otherwise you could end up bending the motor shafts.

My immediate thought for Y-shifts goes toward the cantilever. Check that the cantilever is actually held firmly in place by the X-axis motor assembly housing -- it will have some flex back and forth, but it should not wobble. Check that it does not twist easily (try rotating the end-cap). If the nozzle gets caught by curled overhangs or potentially excess infill as @fuchsr mentions, it has the potential to whack the cantilever assembly forward or backward, or possibly twist it, resulting in a Y-axis shift if it's not rigid enough.

It would help if we had a picture showing how severe the Y-axis shifts are. 

RE: Y-Axis Layer Shift On Mini...Rails and Bearings Are Smooth, Not The Issue. Help!

Reducing the extrusion multiplier to 0.98 seems to have fixed it.

Makes me feel more confidently that it was indeed caused by hitting infill and not a persistent mechanical issue with the printer

RE: Y-Axis Layer Shift On Mini...Rails and Bearings Are Smooth, Not The Issue. Help!

Thanks folks, lots of good insight here. 

The crashing due to over-extruding/cantilever movement are great thoughts, however I am confident this is a belt issue. 
@carlmmii, Yes, the print bed is getting stuck in it's motion. It seems like some sort of belt-bind. When the printer is off and not extruding anything, if I push the print bed back and forth it binds in 2 locations...meaning, the bed stops/gets stuck in 2 different spots along the Y axis. When the bed itself is removed from the sled, and the belt is removed, the sled slides super smooth. When I reattach the bed and belt, it binds when I slide it back and forth by hand. 

I have been busy with other projects and haven't had the time to take it apart again, but I think I need to do it and make sure the pulleys and belt are perfectly aligned. 

Does anyone know if this procedure is documented anywhere? I don't see it in the build procedure. 

Best,
T

RE: Y-Axis Layer Shift On Mini...Rails and Bearings Are Smooth, Not The Issue. Help!

RESOLVED - 

After further investigation, my Y-axis motor was junk. 

Because the slide moved freely without the belt attached, I could tell the issue was with the belt or motor. Spinning the motor by hand SEEMED ok, but it's hard to really get a good feel with the motor still attached. So I removed the motor and examined it. When spinning by hand with no motor or gear it felt clunky. Looking into the back of the motor, I could see that the wave washer wasn't sitting just right and there was plenty of debris built up. I opened the motor and found the wave spring out of place the the back bearing grinding/clunky. 

I got on chat with Prusa and asked for a motor under warranty. They asked how I knew it was the motor and I explained it to them, and sent pictures. After about a 20 minute silence, they agreed to send me a motor but told me by opening the motor, I actually voided the warranty. They said I should have waited for them to TELL me to open it, which I understand... but in an previous debug attempt with them they were sooooo slooooow and I didn't want to wait around. 

The motor arrived in 4 days and the printer is now running fine. 

Thanks for all of the attention, insight, and support of the community. Happy printing. 

T