Print quality - low jerk low acceleration



  • ok I need some help with print quality here. I thought by going slow I would get a nice and smooth print finishes. I have set my jerk to 50, acceleration to 900 and print speed at 50mm/s

    printing regular marvin there's this ringing everywhere… very tiny ringing... any suggestion on how to eliminate ringing? thx



  • I'd start by increasing the instantaneous speed change setting (Jerk). 50mm\minute is really low. So start with 600 or so.



  • increase jerk? isn't that going to make the ringing worse….



  • Show us some photos stephenc it would be nice to see what you mean.

    Try postimage.io to host them.



  • @stephenc:

    increase jerk? isn't that going to make the ringing worse….

    Try it and see.

    "Jerk" is bad expression when applied to 3d printers. Its true name is "instantaneous speed change" which is a bit of a mouthful so people tend to use "Jerk".

    With no "jerk" when you do a move, the print head would have to start from standstill, accelerate up to speed, maintain that speed, then decelerate down to a standstill before starting the next move. For very small moves such as those tiny segmented moves that arcs are made from, the print head would not have time to reach the desired speed so it would simply accelerate a bit, then decelerate to a stop, before starting the next move. The result would be very slow and jerky motion. So if we introduce "jerk" (in the 3d printing sense), the head would start the first move but when it comes to the deceleration phase, it would only slow down until it reaches that instantaneous speed change point (jerk) rather than coming to a complete standstill. The next move would start at that same speed rather than from zero speed and as jerk is only applied where there is also a change of direction, it all results in smoother motion. For sure, too high an instantaneous speed value (jerk setting) can screw things up too. With your setting of 50mm\minute it means that the print head has to slow right down to 0.83mm\sec at the end of a segment before starting the next segment so almost coming to a complete stop. Hence my suggestion to start with 600 which is 10mm/sec.



  • +1 for this, I had Jerk set very low on extruder when I was testing something, the result was that as the extruder jerk was limiting the speed of the other axes and small perimeters/ holes corners were printing very strangely. Edge it up, try edging it up whilst printing, do 10 layers of a small tower with each setting pick the best one.



  • Thank you deckingman for that explanation. Will try higher "jerk" values to validate. Maybe this could be put in wiki? Currently there's topic on it but the content is empty.



  • @stephenc:

    Thank you deckingman for that explanation. Will try higher "jerk" values to validate. Maybe this could be put in wiki? Currently there's topic on it but the content is empty.

    Well "Jerk" or instantaneous speed setting is kind of generic and common to all 3d printers that use slicers which are incapable of producing true arcs (that's all slicers AFAIK). So it's common to all firmwares which is why it probably isn't in the wiki, which is specific to Duet related topics. The setting that you end up with is largely dependant on the kinematics of your machine. There is also some interaction between "jerk", speed and acceleration. It's all part of the "dialling" in process.

    For info and IMO "ringing" is also a term that is often misused. In true terms it refers to certain parameters leading to a sympathetic resonance causing the hot end to "vibrate" for want of a better word. In print terms, the result can look the same as high frequency short, jerky moves which are produced as a result of incorrect speed/acceleration and "jerk" settings. Ringing will only occur at a certain speed which induces the resonant frequency, so if you alter the speed either up or down and you still see same artefacts on the print, then isn't "ringing" in the true sense. If the artefacts go away, then it is true "ringing" and you should avoid using that speed. Or bizarrely as it may sound, you can cure it by increasing the mass of the hot end (at which point I don my tin helmet and await the resultant flack that will come my way).

    Just my twopence worth anyway….........



  • A procedure how to tune speed, accell and jerk could be nice. As mentioned above, these params are to be correct on both XY and E… I have to admit that I don't really know what to do to improve my prints with these params.

    I can see little over-extrusion in the corners. What should I do? Increase jerk? On XY and/or E? What about accell? Should I lower it?

    For example, are there some guidelines to start with decent values, depending on the kinematic, and the weight of carriage?


  • administrators

    If you have over extrusion in corners, try increasing pressure advance.



  • I didn't activate pressure advance yet. My speed/accel/jerk are:

    M566 X900 Y900 Z60 E600 ; Set maximum instantaneous speed changes (mm/min)
    M203 X30000 Y30000 Z1200 E3600 ; Set maximum speeds (mm/min)
    M201 X1000 Y1000 Z100 E3000 ; Set accelerations (mm/s^2)

    Are these params correct? Maximum speed is never reached, I use 50mm/s in slicers. It was just for tests (the carriage does move at these speed, but not usable for printing!).


  • administrators

    Those parameters look ok to me.



  • Ok, thanks. So, I'll try to use pressure advance.



  • Tuning guide big topic, I can offer my method. Maximum speeds: try moving the axes/effector faster and faster until something doesn't look and sound right, such as motor stalling/resonance. Set just below that speed, you'll never actually move that fast when printing.

    Acceleration: trickier as it depends on whether you want to push your machine to its limits, ie print as fast as it can go. 3000 for x, y is a reasonable starting value. Z depends on your machine. Screw drives around 100 works, deltas can go to 9000 or more but there is no need you never move fast in z when printing. E depends on your extruder I've run titans at 9000 it sounds like they're stripping the gears. As a rule of thumb the heavier your moving mass then lower acceleration settings will achieve better (but slower prints). 6000 is quite aggressive, 9000 might work on deltas with 120g effectors. Small details will print more slowly and this is determined by the slicer. If you set low acceleration then with small objects you never reach higher speeds no matter how fast you ask it to go either by setting speed in your slicer or by sliding the speed control faster in DWC or paneldue as every move begins at jerk speed, then accelerates but never gets to the top of the acceleration curve before decelerating. Large moves will show jerk, acceleration then whatever speed you have chosen. You can always set acceleration low for high quality and vice versa.

    Jerk: again it's important to have sufficient not to slow the machine down too much but not so much that you overcome your frame and axis rigidity or you'll see ringing and overshoot on corners.

    There's a lot written about pressure advance so I won't cover that.

    If in doubt start printing towers and vary the settings as you print observe the effect each has and how they depend on one another. You'll learn a lot in the process. Bear in mind that coordinated moves ie moving x, y and e at the same time (typical printing moves) require the firmware to move at the lowest settings of the axes coordinated.



  • You can also throw in filament temperature, filament type and of course nozzle diameter. The maximum acceleration can be calculated if you know the mass of the axis and the torque of the motor. But you'll likely end up setting it lower than this for better print quality. You can set maximum speed to anything you like as long as it's on the high side, as the actual move speed will be governed by the slicer settings or the feedrate that you set for non print moves such as homing and probing. The real maximum print speed will be determined by how fast you can melt filament and will almost always be lower than the capabilities of the printer mechanics and motors.

    If you really have a masochistic streak, then you can try using a mixing hot end which opens up a whole new world of other factors. When you hold filament in the melt chamber for maybe hours at a time without it moving forward all sorts of wonderful things happen like PLA starting hydrolyse which results in over extrusion, and PET-G swelling in the heat break area which screws up retraction. Mixing hot ends should really come with health warning…..........



  • Thank you I really think this level of discussion regarding speed, jerk and acceleration should be in the wiki. it certainly helps me understand the basic and enough of a guidance for me to know what to tweak next.

    Stephen



  • I think there is probably a presumption (correct me if I'm wrong) that those buying Duet controllers, as probably the best controller on the market and one of the most expensive, come to it with some 3D printing experience. Of course, that's not always going to be the case, but a link in the wiki to some other basic guide to 3D printing might be a good idea. There's plenty of them around.



  • I can concur with that presumption… the people that hang around here seem to know a ton about this stuff.... which is awesome btw and I'm glad that I dove into Duet



  • I'd say this is probably the most helpful, polite and free of BS 3D printing forum I've come across.



  • @DjDemonD:

    I'd say this is probably the most helpful, polite and free of BS 3D printing forum I've come across.

    +1.


 

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