Consistent Z lines - Solved



  • Hi everyone and thanks in advance for your help. I’m having some issues with Z lines that I can’t get rid of. Please see attached photos. I can see someone else on this forum has had similar problems, but I don't think this one is related.

    The printer works well in every other way, the X,Y,Z sizes of the test cube are spot on, it’s printed in ABS which exacerbates the Z lines; it looks better on PLA however they are still noticeable. I’ve tried many combinations of temperatures, speeds, acceleration and jerk, in fact I now have so many I could probably build a house with these cubes.

    Printer settings are as follows:
    Corexy (D-Bot) with 2 Z motors on either side of the X axis.
    0.09 layer height
    0.4mm nozzle
    0.48 extrusion width
    240 deg C (Verbatim filament). Have tried 220 deg to 255 deg with no appreciable change in Z lines.
    55 mm/S print speed
    Bowden setup with 3.6 mm retraction.
    Slicer is S3D and have tried Cura as a comparrison

    CONFIG FILE

    ; Configuration file for Duet WiFi (firmware version 1.18.1)
    ; executed by the firmware on start-up

    ; General preferences
    M111 S0 ; Debugging off
    M555 P2 ; Set firmware compatibility to look like Marlin
    M84 S30 ; Set idle timeout
    M667 S1 ; Select CoreXY mode

    ; Endstops
    M574 X1 Y2 Z0 S0 ; Define active low and unused microswitches
    M558 P4 I1 X0 Y0 Z1 H5 F240 T6000 ; Set Z probe type to switch, the axes for which it is used and the probe + travel speeds
    G31 P100 X35 Y0 Z0 ; Set Z probe trigger value, offset and trigger height
    M557 X15:285 Y15:185 S20 ; Define mesh grid

    ; Drives
    M569 P0 S0 ; Drive 0 goes backwards
    M569 P1 S0 ; Drive 1 goes backwards
    M569 P2 S1 ; Drive 2 goes forwards
    M569 P3 S0 ; Drive 3 goes backwards
    M569 P4 S0 ; Drive 4 goes backwards
    M350 X32 Y32 Z32 E32:32 I1 ; Configure microstepping with interpolation

    M92 X161 Y161 Z800 E280:280 ; Set steps per mm
    M201 X3000 Y3000 Z12 E400 ; Accelerations (mm/s^2)
    M203 X15000 Y15000 Z300 E1500 ; Maximum speeds (mm/min)
    M566 X1200 Y1200 Z24 E300 ; Maximum jerk speeds mm/minute
    M208 X300 Y200 Z310 ; set axis maxima (adjust to suit your machine)
    M208 X0 Y0 Z0 S1 ; set axis minima (adjust to make X=0 and Y=0 the edges of the bed)
    M906 X1000 Y1000 Z1000 E900:900 I30 ; Set motor currents (mA) and motor idle factor in per cent
    G21 ; Work in millimetres
    G90 ; Send absolute coordinates…
    M83 ; ...but relative extruder moves

    ; Heaters
    M143 S260 ; Set maximum heater temperature to 260C
    M301 H0 S1.00 P10 I0.1 D200 T0.4 W180 B30 ; Use PID on bed heater (may require further tuning)
    M305 P0 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 0
    M305 P1 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 1
    M305 P2 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 2

    ; Tools
    M563 P0 D0 H1 ; Define tool 0
    G10 P0 X0 Y0 Z0 ; Set tool 0 axis offsets
    G10 P0 R0 S0 ; Set initial tool 0 active and standby temperatures to 0C
    M563 P1 D1 H2 ; Define tool 1
    G10 P1 X18 Y0 Z0 ; Set tool 1 axis offsets
    G10 P1 R0 S0 ; Set initial tool 1 active and standby temperatures to 0C

    ; Network
    M550 PD-Bot ; Set machine name
    M551 PT! ; Set password
    M552 P0.0.0.0 S1 ; Enable network and acquire dynamic address via DHCP

    ; Fans
    M106 P0 S0.3 I0 F500 H-1 ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
    M106 P1 S1 I0 F500 H-1 ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned off
    M106 P2 S1 I0 F500 H-1 ; Set fan 2 value, PWM signal inversion and frequency. Thermostatic control is turned off

    ; Custom settings are not configured

    ; Miscellaneous
    ;T0 ; Select first tool



  • Hi
    I also was experiencing Z lines. I thought I had everything tight however upon further inspection I found that my Y axis had some play. I fixed the play and everything went back to normal. Another area to look at is your extruder. Make sure it is not moving. I had a E3D V6 and I had discovered that it was not entirely secure. There was some play in the grove mount.



  • Thanks for the reply. It was one of the first things I checked and I can't see any play anywhere, to be sure I changed the hotend mount and it made no difference. I've also checked the nozzle and heater block.

    I assumed it was not mechanical because the lines are so consistent on all 4 sides and through each layer.



  • What is your z axis mechanism?



  • 2 lead screws either side of the X axis with anti-backlash nuts. I've coupled the lead screws with a belt but it's made no difference. I have a 6mm aluminum plate with a silicone heater underneath and a PEI sheet on top.


  • administrators

    Experiment with layer height to see how the banding changes. Does the layer height evenly divided by steps/mm (sometimes an issue if using Imperial leadscrews)



  • I asked, as would suggest the same as Tony. You want your layer height to be a full step multiple of a full rotation of the motor. So if the screw turns 1 full rotation to give you 8mm of linear travel, and you have 200 steps/rev (1.8deg) motors then your layer heights should be in 0.04mm multiples, so 0.04, 0.08, 0.12, 0.16 etc… This is partly the reason why 2mm lead is preferable with 1.8 deg motors as the multiple is 0.01 which means any common layer height works great. Factor in any gearing down you have used between the motor and the screws. Or if you have 400 steps/rev (0.9) motors.



  • As DJ said except that from your config.g, I see you have 800 steps per mm which would indicate 4mm lead screws or 2mm with 0.9 degree steppers. In any case, you say that you are using 0.09mm layer height which is a really odd number to choose and means that you would be relying on micro stepping for positional accuracy which is not a good idea IMO.

    In the other similar thread to this, the poster said that he has the problem when sliced using S3D but not when sliced using some other slicer ( Matter control or some such I think). As you too are using S3D, maybe that could be a contributory factor too.



  • Thanks everyone for the comments to date, to clarify a few points. I am running 1.8 degree steppers with 200 steps per revolution, x32 (256 interpolation) microstepping. Before the comments above I was certain I was running M8 leadscrews (8mm per revolution) but now I'm not sure. I measured 1 revolution of travel with my callipers and it was around 8mm, I'm guessing if it was imperial it would be close to that too, the antibacklash nuts are these http://www.makerstore.com.au/product/anti-backlash-nut-block/ and the leadscrew travels through without snagging. I tried printing again with 0.12mm layer height and the results are pretty much the same; see below.

    I have the same result printing from either Cura or S3D.

    How can I tell if the leadscrews are imperial?


  • administrators

    Are you using PID or bang-bang control for the bed heater? Try PID if you are not already using it. I've seen Z banding cured by switching the bed heater to PID before.

    Edit: I've just seen in your config.g file that you are using PID.



  • Ref steps per mm. At "normal" microstepping of 16X, 800 divided by 16 is 50 full steps per mm. I revolution is 200 steps with a 1.8 degree motor so that's a quarter of a revolution, therefore a full revolution would give 4mm, hence my reasoning that your lead must be 4mm. However, I've just noticed that you are using 32x micro stepping so my assumption was wrong. The maths is 800 divided by 32 = 25 full steps per mm = one eight of a revolution = so the lead is indeed 8mm. Apologies.

    So we have 25 full steps =1mm. One step is therefore 0.04mm so you ought to choose layer heights that are multiple of 0.04. i.e 0,04, 0.08, 0.12, 0.16 etc. I've noticed that you say you tried with 0.12 layer height and the results were the same so we can now discount the fact that you may be relying on micro stepping for positional accuracy.

    As I said before, the other OP resolved his issue by using a different slicer to S3D. Maybe try Slic3R? It's free so worth a shot. On the other hand, it could just be an extrusion issue - try printi9ng with the extrusion multiplier set to it at say 95% or 90%. If it makes it worse, try increasing it. For some reason, on my machine, I invariably get best results running at around 90%, even though the extruders are all calibrated.
    HTH



  • Thanks for that. The print in the photo above was done at 90% extrusion multiplier, I've tried 100% and 110% and the cube looks the same.

    The only other issue I can think of, but it's a long shot, is that there is some pull on the hotend from the ptfe tubing. I've ordered a titan extruder and will try that out and see how it goes.



  • I've managed to smooth out the Z lines … mostly. I moved the Z lead screws further back which seemed to do the trick.
    I'm now trying to eliminate the ringing, the strange thing is that no matter what I set Jerk and acceleration to, the ringing is unchanged.

    I would like to clear the ringing so I can fix the remaining Z issues


    Jerk at 500 Acceleration 1000


    Jerk at 1500 Acceleration 3000


    Jerk at 4000 Acceleration 10000



  • What sort of extruder are you using (apologies if you have already said above)? I ask as it seems to be less noticeable at faster head speeds which the 4000 (very high) jerk and 10000 acceleration will give you. Might it be extruder pulsing?

    What type of linear motion device do you have, I do not see this with rails, but rollers and smooth rods might be less good.



  • Also see this thread http://forums.reprap.org/read.php?1,757017 "war against ripples".



  • Do yourself a favor and download the solid 40mm cube from thingiverse then set bottom and top layers to 0 and set parimeters to 1

    Itterate this print over and over again at 60mm/s this will allow you to get better visual feedback over what is happening. My Z lines are non existent because of doing this and it is helping me dial my pressure advance retraction settings in a way that just was not possible to see with a solid cube.

    Also it makes it so it is not such a huge undertaking because it prints so fast.

    The other tip i recommend is that your slicer is set to 5% overlap not 10 or 20. Set your extrusion multiplier to 1.00 and set your extrusion width to match your nozzle tip width. Then change your heat down or up until you get layer widths that match your nozzle width.

    Doing that with your slicer if all your jerk, accell speed settings are right and your mechanics are tightly tuned you will not be able to see layer lines without close inspection (with pla you will need to turn the object sideways and view the layer lines in the light reflection) there will not be any ridges just smoothness the lines are only a reflection of light being diffused when everything is calibrated correctly



  • p.s. use a caliper on the cube walls to verify all is as it should be.



  • Solved!

    I had changed the original H-Bar ends from a 4 wheel version to a 3 wheel version when building the D-Bot. The 3 wheel version moved well and there was no play at all. What I suspect happened was the H-Bar was twisting or flexing slightly as the belts applied force at either end.

    Going back to the 4 wheel version solved the problem.

    Thanks everyone for your help.



  • @bananas:

    Solved!

    I had changed the original H-Bar ends from a 4 wheel version to a 3 wheel version when building the D-Bot. The 3 wheel version moved well and there was no play at all. What I suspect happened was the H-Bar was twisting or flexing slightly as the belts applied force at either end.

    Going back to the 4 wheel version solved the problem.

    Thanks everyone for your help.

    Can I ask which 3 wheel z carriage mod you were using?


 

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