Cura 13.06.4 - Extremely jerky motion for conical walls

[ceramichammer 0]

I just upgraded from 13.01 and loving the new interface and all the sweet options. I printing a simple adapter for a vacuum cleaner with 3 walls and no infill. While printing the vertical part of the cylinder, everything was fine. However, once it got to a 45 degree outward taper, things got really weird. The head was jerking 10-15 times per loop. It looks like the stutter step (knit line) that is made every time it changes z-height but obvious much more frequently than once a layer. I've never seen this jerky motion before. There is nothing obviously wrong in the visual representation of the tool path.

 

[illuminarti 18]

Can you post the gcode file, and let me know roughly which layer the problems start?

 

[znib 2]

I noticed the same thing recently, when I was printing an object with round walls (kind of a cylinder and a torus lying flat on the print bed).

I can post the .gcode this evening when I'm back home.

 

[znib 2]

This is the part I printed. The jerking (going slower and faster again) happened when it did the walls of the circular part. It didn't happend on all layers, on some it made the circular walls with constant speed. I think it was about in the middle where it happened.

I would post the gcode, but I have no idea how I can upload gcode to this forum?

 

 

[lars86 42]

I'm still seeing a lot of this poor motion quality on circular moves. (Cura 14.07)

 

I have exported my stl file with tolerances ranging from a 38MB file, to a 2MB file, and Cura's posted Gcode is the same size ~20MB

 

Any ideas?

 

[Crunchysann 0]

2020 and this is still happening. Changing resolution to 100um from 50um in order to reduce polygon count, and even printing from an SD card to rule out buffer issues did not change this behavior. This results in very rough looking outer wall finish on "any" curved surface. Any idea how to resolve this? In the attached image, you can see that the topmost wall surface is almost perfect,  whereas the rest of th e model seems to not even follow an approximated circular path. All printed in 1 go at 60mm/s (without cooling compensation since multiple parts are printed in batch to allow enough cooling between layers.)

[GregValiant 1,409]

Are you using Accel and Jerk control?  The highest Acceleration that my Ender can take doing circles is 500.  Above that things get jerky.  With Accel and Jerk control turned off it's worse, but with accel at 500 or just below, and Jerk at 8 to 10 it's very smooth.  Yes, it's slower, but the finish is good.

Lowering the resolution helped too, but I had to make the Accell & Jerk adjustment to keep from stutter-stepping.  This thing was made in Shenzhen, not Geneva.

[Crunchysann 0]

No, acceleration and Jerk control in Cura are disabled. My printer runs Marlin firmware (it's a Formbot Trex-3 IDEX with an 8 bit board) and has basic acceleration and jerk control built-in. However, without changing any firmware settings I get much better surface finish in Simplify 3D with identical print settings (as identical as I could make them). I prefer Cura's awesome features though, but it's just this last issue I can't seem to figure out to make a full migration from S3D. Surface finish is good on flat walls but not curved walls.

 

FYI: Just downloaded 4.8 beta in hopes the "Artifact removal in curves." fix would address this issue...but as you can see in the video below, it made no difference. Also, the video doesn't show it, but I can feel the bed make very minor but jerky motion when printing the circular outlines. It seems like the smaller the circular outline, the worst this gets.

 

Gonna try reducing polygon count from my CAD software and see it makes a difference.

 

[GregValiant 1,409]

"Junction deviation accounts for acceleration at every corner. If you use a higher acceleration, then JD will allow you to take corners faster. If you enable JD and use high acceleration for infill, medium for inner walls and low for outer walls, then JD will automatically adjust cornering speed based accordingly for each scenario"

 

"In Marlin 2.0 Junction Deviation is enabled by default"

 

After some more light reading, it appears that "Junction Deviation" (I never came across the term before) has been set in Marlin so all Jerk calculations are done within the firmware.  But it sounds like you should (may?) be able to access some acceleration settings.  Junction Deviation can only be turned off with a re-compile of Marlin.

 

M205 sets advanced settings and from the Marlin site your machine should respond to M205 J<Deviation>.  I have no idea what a proper "deviation factor" would be.  My printer runs Marlin 1.8.1 and responds to accel and jerk settings, but not to a "J" parameter.  Maybe if you peruse a Simplify3D gcode file you would come across an M205 line that would give you a better handle on why it's smoother.  The printer response to an M503 should show you the current "J" parameter setting.  If you were to send an M201 X500 Y500 the printer might change it's acceleration settings.  At any rate, it's something to look at.

 

I found this video on calibrating Accel and JD  https://www.youtube.com/watch?v=Mnvj6xCzikM

Edited November 11, 2020 by GregValiant