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Ultimaker 2 prints non-circular circles

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Posted (edited) · Ultimaker 2 prints non-circular circles



I’m having an issue with an Ultimaker 2, which isn’t making circles properly.


The issue is very apparent on the smokestack of a benchy. It’s also visible as two lines showing up in the hull. The benchy has been printed with the front of the hull pointing towards X+.


The center of the smokestack appears (more) circular somehow. However, I've checked with calipers, it's not round.




Bonus octopus showing the same (Not pictured, but it's also showing the same lines/bulging like on the benchy hull) :




So far I've:
- Checked every belt for tension
- Checked the alignment of the axes, using the printed tool from the support pages (not printed on this UM2, ofcourse)


Those things being fine, I can’t figure what else could be off to make an issue like this show up.

Edited by suspiciouspingpong
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    Posted · Ultimaker 2 prints non-circular circles

    That benchy looks pretty good.  Your most serious problem is underextrusion.  I circled where your walls have gaps.  If the gap is 1/5th as wide as the lines then that would be about 80% extrusion (versus the preferred 100%).  That's pretty bad - I'd fix that first.  Is this a new printer?  I have a nice list of the 30 or so causes of underextrusion on the UM2 but I'd start with the first one:

    Are there more than 500 hours on this printer?  (you can check on the menu).  If so then replace the teflon part.


    Another common cause is printing too fast or too cold. 


    But you didn't ask about underextrusion.  Circular issues you show could be play - you said you checked belt tension (which usually isn't a problem on UM2 because there is a spring hidden in those sliding blocks that the belt passes through to maintain tension).  Another thing to check is friction - if this printer is old it's time to add a drop of light oil to all 6 rods in the gantry.  Push the head around first to feel the friction and then feel if there is a change when you oil 3 rods of just one axis.  Push head diagonally to spread the oil better.


    What is your line width for this print?  That looks like more than .4mm but I guess this is zoomed in more than I am usually used to maybe?


    Not the very topmost layer on benchy will have much worse issues than the rest of the print as the smokestack doesn't have time to cool down.  You get overextrusion on the corner of the stack where it does layer change.


    This benchy isn't too bad but you can definitely fix those gaps and probably your "circle issue" whatever it may be.



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