Hey All -
Long time happy Duet3D user, first time poster here. I need some help with the finishing calibration of a large-format 3D printer build I've been working on. I'm having some pretty severe horizontal banding, and I've run out of ideas on how to resolve it.
First, some context: Hardware is a Duet 3 on a roughly 1m cube belt-driven CoreXY layout printer, with AC heated bed, E3D Hemera + Volcano hotend running direct drive. Printing PLA.
Second, what I've tried:
My immediate thought with horizontal banding is Z stage imperfections, especially since this is a very large, very heavy (150lbs?) bed. However, after reviewing every known mechanical and electrical aspect of the bed, I wasn't able to show any meaningful impact to the banding - and, critically, I discovered when doing test printing that the banding got better/worse as the size of the test print changed smaller/larger. When I was printing large (in XY) test objects, I had intense, high frequency (in Z) banding, and small (in XY) test objects, I had moderate, low frequency (in Z) banding. This indicated to me that it was not likely tied to the Z stage mechanism but something else in the system that was linked either to filament consumption or a time-dependent factor.
Then, my thinking went to extrusion variation. I checked every possible source for filament thickness variation or filament friction, as well as all of the electrical settings around my extruder and hotend, but was, again, unable to see a direct influence on the horizontal banding. However, while doing these tests, I discovered that the banding was not related to filament consumption rate, but it was correlated with layer time - objects & regions with faster layer times showed less horizontal banding.
Finally, where things stand now, and a picture: If I run the exact same test print gcode file, but use DWC to change the speed factor from 50% to 100% to 150%, I get drastically different amounts of horizontal banding in the print - where, somewhat unexpectedly - the faster prints exhibit far less banding. Attached below is a photo of the same print run three times back-to-back. The top one is 50%, middle is 100% (roughly 50mm/s print speed) and the bottom one is 150%.
Any ideas on what might be causing this? It seems like there is some sort of time-dependent layer thickness or flow rate variation in my system.