What too much jerk looks like

(click on the image for a bigger version where it's much more obvious)

This is what I was getting out of the printer last night. This particular piece is EXTREMELY hard on the printer - it includes a bunch of microscopic holes through the bottom dozen layers which are only really there to cause the software to draw reinforcement shells around them, which strengthens the piece in that part, but the printer shakes like crazy and in my case, with the "max_xy_jerk" parameter set to 1200mm/min, caused the steppers to jump a step once in a while, which caused the layers to just drift all over as you can see.

I printed a good copy after this using the old software with no jerk allowed at all, but that results in somewhat lessened print quality on curves and makes the printer noisy and rattley. The ideal solution will be to run with jerk set lower (isn't that always the solution?)

BTW "jerk" in this case is the max allowable instantaneous speed acceleration(*) change on either X or Y axis. Some level of jerk is required to be able to print around curves smoothly while retaining accuracy. Without it the vibration from continually starting and stopping on each arc segment reduces print quality due to vibration and resonance in the printer frame.

Here's an example of what I'm talking about. The top part was printed with Sprinter firmware with no lookahead and no jerk. The bottom was printed with Marlin firmware with lookahead/jerk. The wavy lines you see on top is a result of vibration caused by continually starting and stopping as it goes around the curve. It also rattles and makes a lot of noise while printing like that.
(*) Tnx Kevin for the correction