Vertical Banding Problem and Stepper Waveforms



  • Depends on the design, if I twisted belts on my modified smartrapcore I would not be able to move the y carriages close enough to the pulleys to print on all of the bed without frcing the twisted section into far too small length, which I am sure would have an effect on positional accuracy. I think it depends how much build volume you try to squeeze out of a given size corexy.



  • Do you have a picture of the your modified smartrapcore belts path?



  • But as I said twisting the belts here doesn't help me as I don't get the repeating ripple artefact with my big pulleys.



  • Oh all interesting. I just logged in to post that I feel like I found a major contributing factor to the problem. Perhaps Denos has found the other factor.

    In trying to rule out vibration of the linear shafts themselves (see photos above for my gantry arrangement) I again ran a print with a part in the center and in each of the four corners. Interesting result: The amplitude is reduced in the corners, but the period of the ripple didn't change. If my linear shafts were vibrating I'd expect higher frequency ripple closer to the edges of the bed. If it's mechanical vibration at all, it would seem to be something local to the toolhead.

    Last night I found that if I push my finger against the lower part of the heatsink of the Titan extruder during a print, the ripples pretty much go away. I suspect the heatsink is vibrating, which may explain why the ripple frequency is independent of position on the build plate. It may also explain the reduced amplitude by the edges, but that would require too many words to write right now.

    I ordered the Titan Aero upgrade kit and am redesigning things to suit. I kind of wanted to do that anyway, so if it wasn't the entirety of the problem I'll be OK with that. Will report back when that's working.

    But clearly something is causing the heatsink to vibrate to begin with. I have a standard (non-Aero) e3d Titan on a work printer and that shows no ripple whatsoever.

    Denos, youre test with the idlers is most excellent. I have toothed idlers for my GT2 belts, BUT, the quality control is bad: the holes for the bearings are clearly too small for the press fit, and they grind noticeably when rotated. I installed them anyway because I really didn't think it would cause trouble, but perhaps that's the source of the extraneous vibration that's driving the vibration in the heatsink. Eureka?

    The frustrating thing is, I can't find a reliable (i.e. not super cheap Chinese) source of toothed GT2 idlers. Anyone know? Even good smooth ones seems hard to find. Toothed is preferable for me as my gantry style doesn't lend itself to half-twisting the belts.

    EDIT:

    The toothed idlers I used are from RepRap Champion (not as cheap as I recalled), so, not good.

    ~Justine



  • If the toothed Chinese idlers do not appeal, then consider using large diameter bearings like the F608ZZ bearings I use. Running the belts on the toothed side is not a problem, certainly not for print quality.



  • An update:

    After changing the idlers and switching to the Titan Aero, the ripples are exactly the same, though possibly a bit more crisp.

    I'm going back to blaming some kind of variation in the extrusion speed. Could the large (.8mm) nozzle have something to do with it?

    I'm in the process of making a second toolhead with a .5mm nozzle.

    This weekend going to redo all the motor wires using shielded twisted pairs too.



  • What hotend are you using, with the 0.8mm nozzle? You're right, and it can be related, if the filament does not have time to melt. Do you see any temperature variations?



  • @justine-haupt were you able to resolve the vertical banding? Did you find the reason for the vertical banding? I have a similiar issue.



  • @justine-haupt

    I have been having this problem for a while as well. My theory is that the motors create a vibration that is transferred to the frames and to the z axis, this takes place at a micron level and the vibrations cannot be noticed by the eye.

    Most Industrial machines reduce vibrations by increasing the weight of the frames by adding concrete in them or using a strong concrete foundation. Even the older stratasys machines were built like tanks and they used nema stepper motors as well.

    Vibration meters can be used to measure the vibration of the frames while printing and then stiffeners or weights can be used to increase the rigidity of the machine. This should hopefully reduce the effect of vertical banding.

    Not sure if this is even the correct method.

    Thanks,
    Hussain.



  • @bot

    This is quite interesting, Would like to understand more about this.
    The attached link is not working though.
    Could you guide me to any other resource that explains this calculation.

    Thanks
    Hussain.



  • @hussainsail2002 said in Vertical Banding Problem and Stepper Waveforms:

    @bot

    This is quite interesting, Would like to understand more about this.
    The attached link is not working though.
    Could you guide me to any other resource that explains this calculation.

    Thanks
    Hussain.

    Yes, the link seems broken but I found a new link. It was to a PDF version of the "Gates GT3 Design Manual" in case the link gets broken again.

    https://www.gates.com/resources/resources-library/catalogs/power-grip-gt3-drive-design-manual


 

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