Z axis issue: wrong movement (layers)



  • Hi,
    First of all I want to thanks you all for the support , finally I figure out with the Bl touch issue.
    But now there is a problem with Z axis.
    Since several days my prints are very bad, it seems there is "Z wobble". In my opinion is not "Z wobble" (see attachment) because the error is all around the object (the error is the same in all faces) as if the nozzle was too stick to the print.

    IMG_20191228_233556__01.jpg

    IMG_20191228_233550__01__01.jpg

    So , I tried a lot of solutions but , unfortunately, nothing worked. I've tried:

    • verify if rods are parallel to the frame ---> yes, they are . The frame is perfectly square (3030 profiles) and I tested the parallelism with a dial indicator.
    • verify the movement of X and Y carriages ---> perfect movement, parallel with the frame.
    • verify stability of the heated bed and temperature ---> bed is rigid , temperature perfect
    • verify extrusion multiplier ---> ok
    • verify if the slicer ( prusa slicer ) determinated the problem ---> no , I've tried also with simplify , no differences.
      This is my z axis:
      IMG_20191228_233506__01.jpg

    Than I've tried to leave the two nuts free to move but nothing change, I've also took off the bearing but nothing change.

    And today I've tried to measure with a dial indicator the "Z movement" during print and I've noticed that Z axis moves incorrectly: most of times it does the correct layer height (0.2) and other it does wrong movement (0.26, 0.18, 0.24... )
    Tomorrow I'll post my config.g file.

    So my questions are:

    1. Should I try something else ?
    2. At the moment the board running a 'RC' firmware (2.04Rc ), should I update it?
    3. It could be a mechanical issue?

    Thanks ,
    Alex



  • @zecchi said in Z axis issue: wrong movement (layers):

    At the moment the board running a 'RC' firmware (2.04Rc ), should I update it?

    yes. rc firmware are not supported if they are not the latest.



  • @zecchi this is my config.g :

    config.g

    ; Configuration file for Duet WiFi (firmware version 2.03)
    ; executed by the firmware on start-up
    ;
    ; generated by RepRapFirmware Configuration Tool v2.1.4 on Sun Dec 29 2019 12:57:27 GMT+0100 (Ora standard dell’Europa centrale)

    ; General preferences
    G90 ; send absolute coordinates...
    M83 ; ...but relative extruder moves
    M550 P"ZecchiPrinter" ; set printer name

    M667 S1 ; select CoreXY mode

    ; Network
    M551 P"123" ; set password
    M552 S1 ; enable network
    M586 P0 S1 ; enable HTTP
    M586 P1 S0 ; disable FTP
    M586 P2 S0 ; disable Telnet

    ; Drives
    M569 P0 S0 ; physical drive 0 goes forwards
    M569 P1 S0 ; physical drive 1 goes forwards
    M569 P2 S1 ; physical drive 2 goes forwards
    M569 P3 S0 ; physical drive 3 goes forwards
    M584 X0 Y1 Z2 E3 ; set drive mapping
    M350 X16 Y16 Z16 E16 I1 ; configure microstepping with interpolation
    M92 X80.00 Y80.00 Z1600.00 E96.56 ; set steps per mm
    M566 X720.00 Y720.00 Z30.00 E300.00 ; set maximum instantaneous speed changes (mm/min)
    M203 X6000.00 Y6000.00 Z1200.00 E4800.00 ; set maximum speeds (mm/min)
    M201 X3000.00 Y3000.00 Z100.00 E4000.00 ; set accelerations (mm/s^2)
    M906 X1000 Y1000 Z1000 E1000 I30 ; set motor currents (mA) and motor idle factor in per cent
    M84 S30 ; Set idle timeout

    ; Axis Limits
    M208 X0 Y0 Z0 S1 ; set axis minima
    M208 X310 Y315 Z315 S0 ; set axis maxima

    ; Endstops
    M574 X2 Y1 S0 ; set active low and disabled endstops
    M574 Z2 S2 ; set endstops controlled by probe

    ; Z-Probe
    M558 P5 H5 F120 T6000 ; set Z probe type to switch and the dive height + speeds
    G31 P500 X0 Y-58.5 Z2.5 ; set Z probe trigger value, offset and trigger height
    M557 X15:300 Y12.5:297.5 S57 ; define mesh grid

    ; Heaters
    M307 H0 B0 S1.00 ; disable bang-bang mode for the bed heater and set PWM limit
    M305 P0 T100000 B4138 R4700 ; set thermistor + ADC parameters for heater 0
    M143 H0 S80 ; set temperature limit for heater 0 to 80C
    M305 P1 T100000 B4138 R4700 ; set thermistor + ADC parameters for heater 1
    M143 H1 S250 ; set temperature limit for heater 1 to 250C

    ; Fans
    M106 P0 C"Hotend" S1 I0 F1000 H-1 ; set fan 0 name, value, PWM signal inversion and frequency. Thermostatic control is turned off

    ; Tools
    M563 P0 S"Hotend_0" D0 H1 F0 ; 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

    ; Custom settings are not defined

    ; Miscellaneous
    M911 S22.5 R23.5 P"M913 X0 Y0 G91 M83 G1 Z3 E-5 F1000" ; set voltage thresholds and actions to run on power loss


  • Moderator

    @zecchi said in Z axis issue: wrong movement (layers):

    M203 X6000.00 Y6000.00 Z1200.00 E4800.00 ; set maximum speeds (mm/min)

    1200 may be a bit too fast for your Z axis. Try reducing it by half. Perhaps it's missing steps or binding. Though this is likely offset by the very low acceleration value.

    Can you test the repeatability of your Z axis? Set to a known position marker and then move the z axis up and down many times and see if it returns to the same starting position.

    @zecchi said in Z axis issue: wrong movement (layers):

    (0.26, 0.18, 0.24... )

    What is the full step resolution of your z axis? You show that it's belted to the lead screw. Is there a gear reduction involved? Is the belt slipping the teeth?

    The motor current for the Z axis is 1000. What is the rated current of the motor? Ideally you should set the current to be 70-85% of the rated max current of the motor.

    You're using anti-backlash nuts. They typically are not necessary on the Z axis since there is constant downward force on the bed from gravity and the bed is always dropping away from the nozzle during a print. They can increase friction however to the point they cause binding.

    Have you lubricated the lead screws?



  • @Phaedrux said in Z axis issue: wrong movement (layers):

    Can you test the repeatability of your Z axis? Set to a known position marker and then move the z axis up and down many times and see if it returns to the same starting position.

    Thanks for your replay.
    I'll try later.



  • @Phaedrux said in Z axis issue: wrong movement (layers):

    Is there a gear reduction involved?

    There is a 1 to 1 ratio



  • @Phaedrux said in Z axis issue: wrong movement (layers):

    Is the belt slipping the teeth?

    Belts are quite tight, I don't think they can slip (I hope… no noises , nothing that make me to think they are slipping )



  • @Phaedrux said in Z axis issue: wrong movement (layers):

    Ideally you should set the current to be 70-85% of the rated max current of the motor.

    Ok, it was too low. I set 1200 mA (80% of 1.5A). Unfortunately the error doesn't disappear.



  • @Phaedrux said in Z axis issue: wrong movement (layers):

    You're using anti-backlash nuts. They typically are not necessary on the Z axis since there is constant downward force on the bed from gravity and the bed is always dropping away from the nozzle during a print. They can increase friction however to the point they cause binding.
    Have you lubricated the lead screws?

    I'll try to remove nuts and use normal ones. Also I'll try to clean and re-lubricate the lead screws



  • News:
    -Repetitivety Is ok, tested with a dial indicator
    -I've change the nut. Some improvements but the error doesn't disappear.

    Other advices?



  • it looks like a z-wobble dubble (tripple) check the Z-Axis motion this must be stable and run smooth (it can be a nightmare to find the right position)



  • @SIam
    I've printed a piece in order to fix the lead screws at the exactly center of the two rods, quite good but I didn't solve the problem.

    Any suggestions?


  • Moderator

    @zecchi said in Z axis issue: wrong movement (layers):

    -I've change the nut. Some improvements but the error doesn't disappear.

    Look for more sources of binding. The smooth rods and bearings would be my next target.



  • Also rods are checked. Z axes is absolutely perfect, tested with a dial indicator (only 0.01mm of error in 300mm ). I've also printed a jig in order to have the rods at the same distance.
    But , layer are, still, inconstant (0.24, 0.18, 0.22 ecc...) And this cause the blob (I'm pretty sure about that ).


  • Moderator

    @Phaedrux said in Z axis issue: wrong movement (layers):

    What is the full step resolution of your z axis?

    @zecchi What is the pitch/lead of your lead screws?

    The problem really seems to be similar to trying to print at a layer height that isn't a multiple of the full step resolution of the Z axis.

    https://blog.prusaprinters.org/calculator/#optimallayer



  • @Phaedrux
    2mm pitch. (I ordered the 8mm pitch but it arrived wrong).



  • @Phaedrux
    I've shorter 8mm pitch lead screws. I'll try with them.


  • Moderator

    @zecchi said in Z axis issue: wrong movement (layers):

    2mm pitch.

    Well there goes that theory.

    With a 2mm lead, and 1.8 degree motors (deduced from your 1600 steps per mm on Z) your full step resolution is 0.01mm. So you have no limits there.

    What are the motor specs?



  • @Phaedrux
    So, if my layer height is 0.2mm isn't a problem, correct?

    Motor: 1.5A , 1.8°. Classic 17HS4401 stepper motor.


  • Moderator

    @zecchi said in Z axis issue: wrong movement (layers):

    @Phaedrux
    So, if my layer height is 0.2mm isn't a problem, correct?

    Correct


  • Moderator

    @zecchi said in Z axis issue: wrong movement (layers):

    Motor: 1.5A , 1.8°. Classic 17HS4401 stepper motor.

    I'm unable to find a data sheet that seems close. There are many sub-models of 17H4401 between many manufacturers. I didn't even see any that were 1.5a.

    Can you find a data sheet that seems to match your motor based on what you know about it?



  • @Phaedrux
    Second line of this datasheet:
    17HS2408-MotionKing.pdf

    Now I realize that the seller made fun of me selling this motor as 1.5A instead 1.3A (I re-cecked and in the description is written 1.5A😠 ).



  • @zecchi
    My fault , the line is actually the number eight. So the current is 1.7A. awesome.

    This is the link :
    € 21,62 20%OFF | Nema17 Stepper Motor 42 motor Nema 17 motor 42BYGH 1.5A 38mm 17HS4401 motor 4-lead for 3D printer CNC
    https://a.aliexpress.com/BBHPrX2gL



  • This is the response to M122 command:

    Screenshot_20200104-212211.jpg

    Screenshot_20200104-212217.jpg

    Screenshot_20200104-212224.jpg

    If you see something strange ,please let me know.


  • Moderator

    Everything looks good to me. I think it is mechanical though. I went through a similar ordeal with my own Z axis a while ago. There was a repeating pattern. It wasn't exactly like your pattern but similar in nature. I ended up tearing the entire Z axis apart and replacing many of the chinese belts, pulleys, idlers, lead screws with better quality alternatives as I suspected some eccentricities in the pulleys and possibly some misalignment or bend in the lead screws. I was able to get it mostly eliminated, but it could still be seen in certain lighting conditions, but more faintly.

    Take it apart. Inspect everything. Roll the lead screws on a flat surface. Check the couplers and pulleys. Test the motors and feel how they move in your fingers. Try different motors.


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