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Print head hits/grinds the surface of long, tall prints


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Posted · Print head hits/grinds the surface of long, tall prints

As my PLA prints grow in height, the nozzle increasingly seems to drag across the print surface, making enough physical contact that I can see the print plate actually vibrating.

 

I know this happens with my UM2s, but I think it also happens with my UM3s. Last night, I observed this phenomenon on the print job photoed below. I was using a UM2 and PLA, with a .8 nozzle, printing a .2 layer height. It prints the wall OK. It seemed to print the structure of the infill OK. However, whenever it did one of those rapid repositioning moves, the vibration and sound of contact were very notiecable. I was observing this around hour 5 of this particular job.

 

What's happening here? Is the print somehow expanding in size as the job continues? Are there any settings which I should be tweaking to get the nozzle to give the print surface a bit more leeway? Do infill patternshave any bearing on this?

 

image.thumb.png.3df6f7b16e705947897eab05c7f39398.png

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    Posted · Print head hits/grinds the surface of long, tall prints

    Maybe a problem with the Z screw? Have you checked that there's nothing that could disrupt it's movement and that it is properly greased?

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    Posted · Print head hits/grinds the surface of long, tall prints

    Is the part lifting off of the build plate?  Is you build plate glass really flat?  One of my UM3 glass build plates has a .007"  (0.18mm) bow in the width (X axis) direction while it's perfectly flat in the front to back (Y axis).  I turned it over so that the high point is in the center, rather than at the edges.  If your nozzle is dragging on the part at the sides / edges, but not in the center, you might try turning the glass plate over?

     

    Just a thought . . .

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    Posted · Print head hits/grinds the surface of long, tall prints

    I have the same problem with my Creality and I change the top glass for a Mirror plate because a Mirror plate is verry straight, the thickness is +/-3.4mm. Sorry for my English.

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    Posted · Print head hits/grinds the surface of long, tall prints

    The infill tends to be printed too fast and comes out irregular.  Also the vertical harmonic resonance of the bed is around 10 or 20Hz and this can get amplified on moves over the infill pattern.

     

    This is fixed if you slow down the infill moves to 35mm/sec or change the infill density or move the print towards the back where the bed doesn't vibrate as much.

     

    If you want to print fast I recommend thicker layers and wider nozzles over higher print speeds.  Maybe try the variable infill feature - I love this feature.

     

    And the reason it tends to get worse on taller prints is I think this harmonic resonance builds upon itself because if the bed is bouncing the infill pattern is varying in Z by a sine wave and each layer amplifies the problem more and more.

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    Posted · Print head hits/grinds the surface of long, tall prints

    Thanks for the various comments. I'll do some servicing on the Z screw out of interest. I suspect this is mostly an infill issue, so I will experiment with gr5's advice.

     

    What's with your point about the variable infill feature?

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    Posted · Print head hits/grinds the surface of long, tall prints

    I had this same problem with my old RoboR1 printer, it turned out that my material flow was slightly too high, maybe try making the material flow slightly less than what is now.

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    Posted · Print head hits/grinds the surface of long, tall prints

    If you change the % infill it will change the spacing.  I think the problem is a harmonic resonance of the bed.  The input vibration is from the number of times the nozzle hits the infill per second.  That causes the initial up-and-down shaking (but very gentle initially) and if that frequency is close to the harmonic frequency of the bed then the shaking is amplified.

     

    Just a theory.  But if correct then changing the frequency will fix the problem.  So possibly changing the infill % by a large amount (double or half) might help.  Definitely pushing it to the back of the glass should help.

     

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    Posted · Print head hits/grinds the surface of long, tall prints
    On 6/8/2018 at 9:00 PM, gr5 said:

    variable infill feature

     

    Hi - 

     

    Where is this feature, I have been searching in Cura but no luck.  I am having problems with the nozzle hitting the infill about 5 hours into prints.  Was hoping this might help.

     

    Regards,

    Friedl.

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    Posted (edited) · Print head hits/grinds the surface of long, tall prints

    This can happen if you have a 'static' infill pattern that slowly builds up excess as layers keep piling on. IME, grid is the worst, because it is a perfect repeat. Cubic is a bit better, because at least the lines offset a bit as z-height increases. But gyroid is really the best at minimising this due to the constantly changing pattern, and highly recommend.

     

    You can also set combing to a short distance (maybe 10-30 mm), and set a z-hop during retraction. This way, the print will drop during any large travel moves that are longer than the combing move. Only risks with this are that if you set combing too low you will get excessive retractions, and z-hop has always given me a bit more stringing.

     

    [EDIT] Just realised how old this post is *facepalm*

    Edited by prof_west
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    Posted · Print head hits/grinds the surface of long, tall prints

    @prof_west - 

     

    Thank you for your thorough explanation.  I have since been using Gyroid actuality, it seems to be structurally very strong. 

     

    I also removed the checkbox "Infill before outer walls".  These two settings helped a lot and the problems seems not to occur for the most part.  I will add the Combing and Z-Hop settings you suggested..  

     

    Something else occurs.  Refer to the photo attached.  You can clearly see the change in surface texture where this start (and sometimes stops).  I have paid close attention to during print to try and see what happens.  This is due to the nozzle dispensing little "droplets" of filament on the shell wall when travelling to another position.  When it then passes over these "droplets/beads" you can clearly hear and see the build plate vibrating.

     

    Hopefully Z-Hop fill take car of this.  I might also be my imagination, but it seem to occur more frequently with a particular brand of filament. OR it might be simply sue to the fact that I am using a lot more of this filament as we have plenty in stock - lol

     

    Thanks again!!

    Kind Regards, Friedl.

     

    IMG_0303.jpeg

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    Posted · Print head hits/grinds the surface of long, tall prints

    It really just looks like you are over-extruding a bit. Perhaps try live-adjusting your flow rate down a bit?

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    Posted · Print head hits/grinds the surface of long, tall prints

    Hi @prof_west

     

    hhmm... I would have to sit and watch the print for 12 hours to see when this happens and then adjust? 😄

     

    I will try adjusting flow to 95% and see what happens. I will also try to get a picture when it starts forming the ‘bead-like’ droplets. 
     

    thanks for helping, much appreciated! Been having bed adhesion issues printing with CPE all day, good to have a solution for the PLA print :) 

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