Strange behaviour



  • I just noticed that whenever printing hollow cylinders, specifically the inside wall of the cylinder the print head will slow down to almost a complete stop at the end of the run.
    It lasts almost 2 seconds.
    On first look I thought it was pausing at a complete stop, but it is actually moving at an incredibly slow speed.
    I put my fingers lightly on the filament and I can feel it retract ever so slowly at the distance (i'm guessing) that I have set for retraction in my slicer, during this slow down.

    When printing the outside of the wall, it behaves as normal.
    I have also noticed this sometimes on the corners of a square, on the inside wall.
    Printing speed doesn't seem to matter. It will do it at any speed I have set.

    Anyone ever experience this? I did a search but didn't find anything exactly matching my problem.


  • administrators

    Can you share the Gcode? If you are using pressure advance, does turning it off make any difference?



  • Surely. But forgive my ignorance.
    Do you mean the slicer generated gcode for the print?

    I haven't tried it with pressure advance off. But I surely will and report back!



  • Just in case you did mean the gcode for the print:

    https://dl.dropboxusercontent.com/u/15733846/20mm%20Cube_Cylinder%20Test.gcode



  • Hi Scott, you just recently enabled pressure advance. Share your jerk speed and accell settings.



  • [[language]]
    ; Drives
    M569 P0 S0 ; X goes forwards
    M569 P1 S1 ; Y Reversed
    M569 P2 S0 ; Z goes forwards
    M569 P3 S0 ; Extruder goes forwards
    M350 X16 Y16 Z16 E16 I1 ; Configure microstepping with interpolation
    M92 X99.5 Y99.5 Z399.7 E79.9 ; Set steps per mm
    M566 X900 Y900 Z12 E120 ; Set maximum instantaneous speed changes (mm/min)
    M203 X18000 Y18000 Z500 E1200 ; Set maximum speeds (mm/min)
    M201 X500 Y500 Z250 E250 ; Set accelerations (mm/s^2)
    M906 X1200 Y1200 Z1200 E1200 I30 ; Set motor currents (mA) and motor idle factor in per cent
    M84 S30 ; Set idle timeout
    M572 D0 S0.1	;Pressure Advance
    
    

    As coincidental as it was it never occurred to me that Pressure Advance was the culprit.
    I guess I was so giddy about being able to hit 100mm/s I got dumb.

    I am at work now, (I think you guys are 6 hours ahead) and will get off in 4 hours. I will disable PA, test it out and report.

    Thanks so much!!!



  • I've got pressure advance turned off at the moment because there is an issue using it with multiple extruders but when I did have enabled, I found I had to increase extruder jerk from 600 to 1200 so as yours is set to 120, I'd guess that would be the culprit.



  • I will change it tonight.

    What is a good speed to set it at? Is having a high speed setting, such as what I have on the X and Y detrimental even though I have no illusions of ever going that fast?



  • your settings are very low…. 3000 mm/m jerk and max speed = 50mm/s.... your slicer defaults to 55mm/s speed for retractions. so i recommend upping max speed and jerk for extruder to 3600 and even faster if you want to do faster retractions.

    You have a solid and light build, i do not see why you cant up your jerk and accell settings for x and y as well... just push it until the quality of print starts to degrade for your target speed



  • Honestly with such low extruder settings you probably dont know what your best x and y settings are yet because of how low those were.



  • @Scottbg1:

    I will change it tonight.

    What is a good speed to set it at? Is having a high speed setting, such as what I have on the X and Y detrimental even though I have no illusions of ever going that fast?

    Your X and Y speeds will mostly be limited to by the speeds you set in your slicer and also by your accelerations. So the maximum speed in config.g is largely irrelevant IMO. I just use it as sort of safety feature in case I ask the printer to do something stupid. One way to decide is to work out what maximum non-print speed is likely to be and set it to that. For example, I like to use a highish non-print move speed of 350mm/sec which is 21,000 mm/min. Another way of doing it is to calculate the maximum speed you could possibly achieve for the acceleration you have and the longest move you can do (bed size). So for example assuming the longest move is 200mm and you have your acceleration set to 500mm/sec^2 then the maximum speed you'll get up to is sqrt (2accelerationlength/2) = about 316mm/sec or 18,960 mm/min. So setting the maximum speed to anything above that will have no effect. BTW I'd say your acceleration settings are on the low side but it depends on what your motors torque characteristics are, the mass that you want to move, and how rigid the frame is. My X axis mass is a whopping 1.67kgs and calculating the acceleration possible with the torque available for the motor, the number comes out at around 1200 mm/sec^2.



  • Thanks for that. It's apparent I have so much more to learn.

    I am sitting here thinking that most of the troubles I have experienced were most likely due to me trying to drive it harder than it could go.
    And yes, I haven't been able to get my retraction settings to work right yet. I have had very bad oozing and over extrusion at the beginning and end of a run. I have set my coast and wipe settings to some crazy numbers that I didn't feel good about.
    I was beginning to think that the PLA+ was more akin to PETG than anything. It was crazy.

    I guess I have some more tweaking to do tonight!
    With that, I want to disable Pressure Advance, and play around with my slicer once I up the jerk settings, and see how well I can get it to behave with retraction settings only. Then I will enable pressure advance and see exactly what the benefit it offers.



  • @Scottbg1:

    …..........
    With that, I want to disable Pressure Advance, and play around with my slicer once I up the jerk settings, and see how well I can get it to behave with retraction settings only. Then I will enable pressure advance and see exactly what the benefit it offers.

    Definitely the best approach. Cut down the number of variables as much as possible otherwise you'll just get lost.



  • @deckingman:

    @Scottbg1:

    I will change it tonight.

    What is a good speed to set it at? Is having a high speed setting, such as what I have on the X and Y detrimental even though I have no illusions of ever going that fast?

    Your X and Y speeds will mostly be limited to by the speeds you set in your slicer and also by your accelerations. So the maximum speed in config.g is largely irrelevant IMO. I just use it as sort of safety feature in case I ask the printer to do something stupid. One way to decide is to work out what maximum non-print speed is likely to be and set it to that. For example, I like to use a highish non-print move speed of 350mm/sec which is 21,000 mm/min. Another way of doing it is to calculate the maximum speed you could possibly achieve for the acceleration you have and the longest move you can do (bed size). So for example assuming the longest move is 200mm and you have your acceleration set to 500mm/sec^2 then the maximum speed you'll get up to is sqrt (2accelerationlength/2) = about 316mm/sec or 18,960 mm/min. So setting the maximum speed to anything above that will have no effect. BTW I'd say your acceleration settings are on the low side but it depends on what your motors torque characteristics are, the mass that you want to move, and how rigid the frame is. My X axis mass is a whopping 1.67kgs and calculating the acceleration possible with the torque available for the motor, the number comes out at around 1200 mm/sec^2.

    Thanks for that, I always wondered what the math was, I have only ever used the reprap calculator. Yeah he has a pretty light but what looks rigid setup with carbon fiber linear rods which is why I recommended he try out some better accell settings but only once he fixes his extruder settings so it can keep up.



  • @Scottbg1:

    Thanks for that. It's apparent I have so much more to learn.

    I am sitting here thinking that most of the troubles I have experienced were most likely due to me trying to drive it harder than it could go.
    And yes, I haven't been able to get my retraction settings to work right yet. I have had very bad oozing and over extrusion at the beginning and end of a run. I have set my coast and wipe settings to some crazy numbers that I didn't feel good about.
    I was beginning to think that the PLA+ was more akin to PETG than anything. It was crazy.

    I guess I have some more tweaking to do tonight!
    With that, I want to disable Pressure Advance, and play around with my slicer once I up the jerk settings, and see how well I can get it to behave with retraction settings only. Then I will enable pressure advance and see exactly what the benefit it offers.

    I forget which thread, but I believe it was DC42 who recommended that pressure advance get tuned with retraction off then slowly increasing retraction after tuning PA, but yes make sure you get good results without it because you have had some extrusion issues that should be sorted first.



  • Ok….

    I upped my jerk and acceleration speeds to this:

    [[language]]
    M566 X1000 Y1000 Z12 E1000 ; Set maximum instantaneous speed changes (mm/min)
    M203 X12000 Y12000 Z375 E9000 ; Set maximum speeds (mm/min)
    M201 X1000 Y1000 Z150 E1000 ; Set accelerations (mm/s^2)
    
    

    I also disable pressure advance.
    I set the retraction settings to this:

    I also disabled ooze control completely.
    This is what I got at 100mm/s

    https://dl.dropboxusercontent.com/u/15733846/Retraction%20on.mp4

    I then disabled retraction completely and enabled Pressure Advance.
    I kept upping the value until it started laying lines nice and neat with no breaking.
    I ended up with:

    [[language]]
    M572 D0 S1	;Pressure Advance
    
    

    This is the result:

    https://dl.dropboxusercontent.com/u/15733846/Retraction%20off.mp4

    What do you guys think?



  • I forget that it's after midnight for you guys when it's still evening for me.

    I have changed a few more things as my night has progressed.
    I turned retraction back on, yet at a much lower rate to start out.
    I tried 3mm retraction with the Pressure Advance rate I had set.
    I don't like it.
    I ended the night with bring the retraction length back up, increasing the retract speed a little more and dropping the Pressure Advance back way down.

    I printed out a very small part for my webcam.
    I brought the speed down to 40mm/s because it has very small snap/fit pegs on it and I wanted them as uniform as possible.
    That slow a rate and that small of a part, the lines were separated and inconsistent with the PA set so high.
    And the part was pretty weak. The pegs snapped off when I was lightly cleaning stringing off with my fingers.
    I printed it PLA+ which is surprisingly strong compared to regular PLA.
    I printed it again but this time I upped the retraction settings because it was stringing badly, and I lowered the Pressure Advance.
    This time it was much, much better. It was minimal stringing and much stronger.

    I'm tempted to print it again with Pressure Advance disabled, as I really don't think I am gaining anything from it. At least on small stuff.
    If I understand it right, PA increases the extruder speed exponentially when beginning a run to compensate for the PTFE tube giving under pressure and causing under-extrusion at the beginning of the run. And then the opposite as it is coming to the end.
    My simple mind figures that would only be beneficial on larger parts with a lot of flat real estate to print.



  • You can actually observe the effects of pressure advance if you start a print without it… let it go and every quarter inch send pressure advance to different levels using the gcode console... it shows its best results on large parts but does affect small parts.

    Test with settings like 1.0 1.2 1.32 etc

    the best way i have found to dial in PA is at 60mm/s printing a 40mm cube with 1 parimeter and 0 top or bottom layers and 0 infill.

    You can really see the affect doing so.

    As far as your settings go, DC42 is going to have to chime in here because my understanding of jerk settings is for short speed changes which is what retraction and pressure advance do.

    Personally i have jerk and max speed set to the same for my extruder because if jerk is taken into account for these short movements then there is no way you are achieving 55mm/s

    But DC42 will have to clarify if my assumption is correct on this.



  • I couldn't sleep so I delved further into experimenting with settings.

    I've since changed my config settings to this…

    [[language]]
    M566 X1500 Y1500 Z12 E1500 ; Set maximum instantaneous speed changes (mm/min)
    M203 X12000 Y12000 Z375 E9000 ; Set maximum speeds (mm/min)
    M201 X1500 Y1500 Z150 E1500 ; Set accelerations (mm/s^2)
    
    

    Pressure Advance back to 0.2.

    I went higher on the jerk and acceleration settings and but I thought the printer would detonate.
    And the print quality went down. So I lowered them to what I have shown above.



  • Is your extruder a geared extruder?


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