Cyclic Z-Step Issue

  • Hello all! I've been trying to find some good information about an issue I'm having, and it doesn't seem like anyone has experienced exactly what I'm dealing with, so I figured I would start a new topic on it. After installing my new DuetWifi on my Rostock MAX V2 this past weekend (along with a PanelDue 7i, JohnSL FSRs, and TrickLaser Carbon Rods), I ran some print tests and, while I worked out some bugs, there is one that won't go away. Every so often, my layer will act like it was squished and print slightly larger than it should, then go back (somewhat) to normal. It will do this on almost every Xth layer(s), and did NOT do this before the upgrade. I thought it might be extruder stepping needing calibration, but I just calibrated that down to about 99% accuracy and the issue is still prominent (albeit a little less than it was before the extruder calibration).

    Has anyone experienced this after an upgrade and, if so, what was your solution? Normally I wouldn't be as buggered by it but I have people queued for prints and while I appreciate their patience while I upgrade/troubleshoot, I am sure they won't want to wait forever 😅 I'll be more than happy to upload any information required, and have also included a photo that depicts what I am seeing. I've read in other places that it could be mechanical but I feel that pertains more to Cartesian printers and not Deltas, and I'm less inclined to believe that is the cause since it wasn't doing this before the upgrade.

    Any help would be super appreciated!!! Thank you in advance!!!!

    If you have trouble seeing the photos, let me know and I'll upload them somewhere else.
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  • Moderator

    Start with your config.g to give us an idea how your printer is configured.

    Those lines of bulging extrusion look like z banding, but you're right that's typically more an artifact of single z axis prints rather than Deltas.

    You mention also changing your rods and installing an FSR on your bed, so you have made some mechanical changes as well, so don't discount mechanical issues so fast.

    Are you by chance using bang-bang mode on the heated bed?

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  • @phaedrux Here is my config file
    I am indeed using bang-bang mode. Would that have this effect though? That seems pretty intense of an effect for the prints, unless bang-bang mode is affecting the head's heating/movement?

    ; Configuration file for Duet WiFi (firmware version 1.21)
    ; executed by the firmware on start-up
    ; generated by RepRapFirmware Configuration Tool on Sun Sep 23 2018 14:52:19 GMT-0400 (Eastern Daylight Time)

    ; General preferences
    G21 ; Work in millimeters
    G90 ; Send absolute coordinates...
    M83 ; ...but relative extruder moves
    M555 P1 ; Set firmware compatibility to look like RepRapFirmare

    ;*** The homed height is deliberately set too high in the following - you will adjust it during calibration.
    M665 R139.7 L300 B139.7 H361 ; Set delta radius, diagonal rod length, printable radius and homed height
    M666 X0 Y0 Z0 ; Put your endstop adjustments here, or let auto calibration find them

    ; Network
    M550 PRostock Max V2 ; Set machine name
    M552 S1 ; Enable network
    ;*** Access point is configured manually via M587
    M586 P0 S1 ; Enable HTTP
    M586 P1 S0 ; Disable FTP
    M586 P2 S0 ; Disable Telnet

    ; Drives
    M569 P0 S1 ; Drive 0 goes forwards
    M569 P1 S0 ; Drive 1 goes backwards (compensation for wiring)
    M569 P2 S1 ; Drive 2 goes forwards
    M569 P3 S1 ; Drive 3 goes forwards
    M350 X16 Y16 Z16 E16 I1 ; Configure microstepping with interpolation
    M92 X80 Y80 Z80 E91.725 ; Set steps per mm (originally E663)
    M566 X1200 Y1200 Z1200 E1200 ; Set maximum instantaneous speed changes (mm/min)
    M203 X18000 Y18000 Z18000 E1200 ; Set maximum speeds (mm/min)
    M201 X1000 Y1000 Z1000 E1000 ; Set accelerations (mm/s^2)
    M906 X1000 Y1000 Z1000 E800 I30 ; Set motor currents (mA) and motor idle factor in per cent
    M84 S30 ; Set idle timeout

    ; Axis Limits
    M208 Z0 S1 ; Set minimum Z

    ; Endstops
    M574 X2 Y2 Z2 S1 ; Set active high endstops

    ; Z-Probe
    M558 P4 H5 F120 T15000 ; Set Z probe type to switch and the dive height + speeds
    G31 P100 X0 Y0 Z-0.2 ; Set Z probe trigger value, offset and trigger height
    M557 R139.7 S20 ; Define mesh grid

    ; Heaters
    M305 P0 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 0
    M143 H0 S120 ; Set temperature limit for heater 0 to 120C
    M305 P1 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 1
    M143 H1 S280 ; Set temperature limit for heater 1 to 280C

    ; Fans
    M106 P0 S1 I0 F500 H1 T45 ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned on
    M106 P1 S1 I0 F500 H1 T45 ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
    M106 P2 S1 I0 F500 H1 T45 ; Set fan 2 value, PWM signal inversion and frequency. Thermostatic control is turned on

    ; 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

    ; Automatic saving after power loss is not enabled

    ; Custom settings are not configured

  • Bang Bang mode could definitely be the culprit. Quickest way to test is to print PLA with the bed-heating disabled.


  • Moderator

    Bang-Bang heater mode on the bed heater is a very common reason for such banding. Rapid heating, followed by rapid cooling, can cause enough flex/warping/expansion to over squish a layer. Consider that even a difference of 0.05mm is 25% of a 0.2mm layer.

    As @adavidm said, the easiest way to test is to print PLA either without the heated bed, or turn it off after the first layer and see if the bands persist.

    Regardless, it's a good idea to do a PID tuning of your heaters to get consistent temps.

  • Gents! Bang-Bang was definitely the culprit. I ran a PID calibration and tuning today and then redid my 3D benchy and the issue was gone completely! I thank you for your input as it was a very quick fix and got me back to my original rambo quality + a little extra. Now I just need to fine tune some things with the rest of the printer and I should be at max quality! Here is the before and after adjustment; night and day difference!
    If you have any additional input to other little tuning suggestions based on the print quality, I'd love to hear them! I already know that retraction will have to be adjusted for the stringing, probably a coast for that back left corner build-up (I use a fixed location for each starting layer to minimize surface blemishes), and increase top layer thickness as I have small gaps, but some of the random blemishes have me a little curious. You can see one on the good quality boat near center-middle. That and one half of the arches/circles come out clean while the other half come out somewhat unsightly (left/right halves, not top/bottom halves). Heck, that could be all a product of where I have the fixed starting point! More testing tomorrow 🙂

  • Moderator

    Glad that solved it for you!

    Only advice I can give you for best results is to target 70-85% of max rated current for your motor current, and then to experiment with jerk and acceleration values. Then try to dial in a good pressure advance value.

    Happy tuning.

  • Hey all! So I come back with a question. I'm seeing the same issue, however it's not nearly as frequent. Picture shows the frequency. The bed is rock steady at 60C with PID control. Same process used for whole print too (sliced in Simplify3D). Any input is appreciated! Seems like a temperature thing but unsure.

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  • Moderator

    @mobiusone if you look at the gcode preview can you see if those bands match up with sections where the layer start seam also match up?

  • administrators

    Also check that heater power compensation for VIN voltage variation is enabled. To do this, send M307 H1 and see whether the calibration voltage is approximately the same as your VIN voltage (in which case it is enabled), or zero (disabled).

  • Thanks for the input! I'll take a gander when I get home. Going to be reprinting this item again due to other issues that arose so I'll have time to check all these items as well.

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