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Printing problem

Discussion in 'Troubleshooting' started by Lance Weston, Feb 3, 2024.

  1. Lance Weston

    Lance Weston Active Member

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    I have two identically configured printers set up. I am using Cura 5.6.0. I am getting little indents of maybe .2mm long on my prints. The indents are random. They are small enough that they are barely visible to the naked eye.

    I have used a rod to clear the print path from drive gear straight through the print head I have run a .4mm need through the print head. I use oilers on both machines. This phenomena is dependent on the part I am printing, with some parts not showing it at all.

    My nozzles are hardened steel and I am printing PLA+. This occurs with every brand I try.

    Any thoughts?

    More info:

    I use 0.9 degree steppers for x and y. I use 8825 drivers. I was setting the drivers to 32 steps. That led to 320 steps per unit on x and y and 285 on extruder. I posited ( original Robo settings) that the processor could not keep up. I set the stepper drivers to /8 for x and y returning them to 80 steps/unit and the extruder driver to /16 and 142.5 steps/unit.

    To my surprise the dings were almost totally gone and print quality improved. Printer noise increased.

    Some Calculations:

    If the x or y is traveling 1mm using 320 steps. it would seem that the extruder should output a 1mm long trace using about the same number of steps. The drive gear is about 6mm in dia and the filament is 1.75 mm dia. (6+1.75)x 3.14 = 24.335 mm/rev. if the print nozzle is .4 mm and the layer is .2mm then (1.75 x1.75) /(.4x.4) =19.1mm x 24.335 mm/rev X 2 for .2mm layer gives 912 mm/rev

    .44steps/mm x32 only yields about 14 steps/mm.

    This seems to be terrible.

    More Calculations:

    The cross sectional area of 1.75mm filament is 2.405 mm^2
    .4mm nozzle x 0.12 mm layer is 0.048 mm^2

    So the trace is 50mm long for every mm of 1.75 filament extruded.

    145 steps/mm extruder divided by 50 mm is 2.9 steps/mm. This could explain the fine vertical lines I have seen on prints. I am looking at the individual steps.

    I am going to put in a 0.9 degree stepper, am using the Partsbuilt system board with 8825 drivers set to 32. That will increase from 2.9 steps/mm to 11.6 steps/mm of a 0.12mm layer.

    Will report when finished.


    Surprises

    The random dings seem to be caused by printing at too high a temp. Printing PLA @ 235 covered some problems but generated random dings.

    Larger repeatable dings seem to be caused by too large jerk settings and I am trying to find optimal settings. I will report when I figure out optimal settings.
     
    #1 Lance Weston, Feb 3, 2024
    Last edited: Feb 19, 2024

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