I’ve noticed an interesting pattern in the raft of my prints on my new printer, which you can see on the right side of the raft in this picture. (Ignore the stuff on the upper right, that’s just the next layer of the raft)
The printer head actually seemed to slow down over this area, which, due to the hysteresis of the Bowden tube causes some more plastic to be extruded over those parts. It occurs right at the apogee of the X and Y carriages as it is laying down each individual line. In other words, it occurs around the point in the current line segment where the X and Y carriages change direction.
It really feels like a firmware problem rather than a hardware problem, because the extruder motor slows down a little bit over this area as well.
Anyone have any ideas?
Try slicing with a different slicer. It may just be how that slicer it interpreting that file.
This is occurring within individual line segment commands, so using a different slicer shouldn’t make a difference.
Looks like a mechanical issue, but to know what kind, I’d need to know more about what type of printer it is and how it’s built.
What are your acceleration settings, and what kinda printer is this?
It’s a delta. I’ll post more info later.
I suspected that it was a delta. I’m betting that line where it’s thicker is perpendicular to the line running form one of the three columns to the center of the platform (the point equidistant between all three columns), right?
I think figured it out. It seems that it is a software problem…!
The problem has to do with the fact that acceleration in marlin is based on the carriages rather than the head platform. The head platform may be moving in a straight line with a constant velocity, but the velocity of the carriages is always changing. Once those velocity changes exceed DEFAULT_XYJERK and DEFAULT_ZJERK, then that causes the acceleration mechanism to kick in, which leads to a discontinuity in the velocity of the head platform. This leads to a thicker extrusion due to the hysteresis of the Bowden tube.
Easy enough to test, and the assumption that Marlin delta speed is really “carriage” speed and not “effector” speed is correct. I’ve never experienced the artifact you have, but maybe I had my acceleration & speed set high enough to avoid it. As an FYI, Smoothieware’s delta solution is based on effector speed as opposed to carriage speed as I recall.
