Uneven layers



  • Re: Uneven layers

    I'm still trying to solv this annoying problem, any help would be appriciated!

    I've now upgraded my whole Z axis to use 3 independent steppers which are belt driven with an reduction of 1:3, 200steps/mm.
    I've checked with a gauge and the bed doesen't move in X/Y at all, so I'm completley out of ideas now.. also I have remade the whole X/Y setup to use a direct drive BMG with doubble mgn9 carriges on X and 4x mgn12 carriges on Y (2 on each side).

    71969685_427704314613636_1311561168271179776_n.jpg



  • did you change the lm8uu housing ?



  • @Veti Hi,

    No I still have the SCJ16UU housing.
    I'm thinking of maybe replacing thos with LMEK16LUU instead, but that would be a 60€ expense, and I can't say for sure that it would fix my problem.



  • I recently posted a thread about a very similar looking problem where I guessed it was caused by overextrusion. I was able to reduce those symptoms by dialing down the flow rate from 100 to 90%. This presumably only changes the severeness of those artifacts, it doesn't solve the root problem (unless the root problem is indeed overextrusion, so first check that if you haven't already).
    The artifacts on my prints were also partly related to a slightly sticky linear guide on my print bed so you might want to check that also.
    And lastly, since you're apparently using a 0.8 mm nozzle (I quickly glanced through your linked post) you might not really have another choice than to live with a slightly worse optical quality. My guess is that a coarser nozzle emphasizes the unpredictable behaviour of a viscous polymer string that is squished by a nozzle. So that's probably the price to pay for way faster 3D printing 🤷



  • @Eumldeuml Very interesting indeed, it looks very similar to my problems.
    I have actually changed the nozzle to a 0.6mm on this print, but still had the same issues (tried with a 0.4mm as well).

    When I lowered the extrusion rate the lines did get better, as in your tests, but it doesent disapear..
    I'm not sure how exact you can print, I rearly see any pictures of prints taken in the worst possible lightning (as I do).



  • I tried to highlight the lines on the pictures in my thread too (with light from above in a very shallow angle) 😉
    When I looked at the layers under a semi-professional microscope (meaning that it has graduations in the lens) I discovered that the layers weren't always exactly 0.3 mm thick which led me to check the Z-axis for binding spots and other 'wobblynesses'. I couldn't really find some but I still realigned the guides and that improved the problem a little bit. So maybe you could measure the travel of the bed in various spots with a dial indicator (or calipers but that is quite a wonky and unreliable setup) and check if it moves in equal intervals.



  • @Eumldeuml YEah I actually did that yesterday.
    As I have 3 seperate steppers for Z I measured them all and when requested 0.32mm i got between 0.30-0.32mm every time so I don't think that's where the problem is.
    The part allways comes out with the correct height as well.

    One thing I notice from your post was that link from one of the posts, and by that I should have a line width of 0.92mm and not 0.72mm as I have atm.. I will try that when I get home and see if there's any diffrence.



  • @Eumldeuml Nope, diden't do anything 😞



  • Check the X any Y axis as well. Home them, move them somewhere to middle with controls and then try to move by hand. There should be no play while the motors hold position.



  • @OBELIKS Hi,

    X and Y are very stable, also the Y axis has a 1:3 reduction and X axis a 1:2 reduction.



  • @Haggan90
    Its mechanically interesting that your wall variations match each other on the x face and the y face. Do the indents and outdents match each other on the positive and negative x face as well? In other words, if you turn your cube to see the side profile of both X walls, do the indents look like

    \ \
    / /
    \ \ indicating some kind of wobble

    OR

    \ /
    / \
    \ / indicating some kind of compression or extrusion issue

    What kind of lead screws are you using and at what pitch?

    What is the infill % and type you used on this print?

    What power setting do you have on your Z stepper motors?

    Are you using bed mesh leveling and have you updated it recently?



  • @spudaddict Hi!

    It's more like the second option, some kund of compression or extrusion issue but very random.

    /
    /

    I'm using 3 seperate sterppers for Z, each one with a 3:1 reduction gearing and 10mm steel enforced GT2 belts.

    This was printed with 0% infil and 2 perimiters.
    I think they are running at 1A each, rated to 1.3A I think.
    No, only true bed leveling with the 3 Z motors.



  • Could you try to print the cube rotated by 45°?



  • @OBELIKS I will try that when I get home from work tonight 😃



  • @Haggan90
    I see you have tried a lot of options already so kinda stretching on some additional ideas:

    On the reprap config tool, wondered what motor current you set for the Z stepper motor.

    Have read the Duet board needs backside cooling as well as driver cooling. Any chance you are having an overheating issue?

    I'm a mechanical engineer and new to the Duet so total N00b with firmware - but I think the true bed leveling (G32) is for independent z motors (each with their separate driver). If your 3 Z motors are tied together to a single driver (electrically or mechanically) you should be using the bed mesh compensation. Probably not related to the issue you are having, but can improve your prints.



  • @spudaddict said in Uneven layers:

    Have read the Duet board needs backside cooling as well as driver cooling. Any chance you are having an overheating issue?

    You cool the stepper drivers by cooling the back of the board - the stepper driver chips have metal pads on the underside which are soldered to the PCB to allow them to transfer the heat from the chip to the PCB. The mass of little holes (thermal vias) are to help in transferring this heat to the large copper areas under each stepper driver

    Cooling the back of the board is enough. The top of the chip is plastic and therefore does not help in dissipating heat from the internals.



  • @Haggan90 Your image is very interesting: in the upper part, Y layers are going outside, X inside. At the middle just below the X letter, X and Y both inside. Could you please look how it behaves at the back for those specific layers: if to inside, then at the opposite also to inside, or to outside? If to the other direction, them it would mean it is printed in correct lemgth, but simply shifted. Then I think the LM12/LM8 ball carriages may have play (or something other like bed screws) and at a Z movement the bed shifts sometimes. You could test by a spring at the opposite side at the bed, so the carriage is always running at one side on the shaft. Hope you understand what I mean....

    I mean: is it (exaggerated, every color is a layer) case 1 or 2?
    layer1.jpg

    Case 1 could be a cause like above.
    Case 2, it could be something like different warping because of different temperatures of the nozzle.



  • Ok. I read your other thread, so case 2. I think it has to do with the temperatures, or your filament clogs the nozzle sometimes or temperature is too high (what are the black dots in your sample?).



  • One more thing you could try is setting A and B stepper to endstop position for every layer you begin, so errors like spinning/slipping gears will show up (because if you reset at each layer, the error will disappear). Maybe you have spinning gears all the time, but it shows up after long movements like at the layer changes.


  • administrators

    @JoergS5 said in Uneven layers:

    Ok. I read your other thread, so case 2. I think it has to do with the temperatures, or your filament clogs the nozzle sometimes or temperature is too high (what are the black dots in your sample?).

    Also make sure you have run heater tuning on the bed heater and you are running it in PID mode. Running the bed heater in bang-bang mode can cause banding like that.


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