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Gaps in circles


3dnerd
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Posted · Gaps in circles

Hi,

I use Cura 4.11.0 and an Ultimaker 2 with Olson Block and created a holder for a pcb.
My problem is (as one can see in the image below) there are gaps around the holes.
Everywhere else the top surface is quite good but where the holes are the circles do not touch for some reason.

Other rounded parts as the rounded corner in the front are closed. It seems to be an issue only where complete circles are.

 

GapInCircles.thumb.png.9e4b1c01f2785c5905449891bc9e91c3.png

 

Does anybody face the same problem?

How can I fix this?

Thanks for any help!

 

 

 

GapInCircles2.png

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    Posted · Gaps in circles

    I get that sometimes - that's underextrusion.  When I start to get that on my UM2 I know I need to replace the teflon part soon.  Yes the rest of the print looks fine but that's still underextrusion.  Pretty sure.  You can test it with the temporary fix below to see if it gets better.

     

    You can get it if you print too cold or too fast.  The temporary fix is to cut the speed to 60%, increase flow to 105% and increase temperature by 5C (but don't increase temp for ABS as ABS clogs too easily as you get hotter - PLA can print up to 240C ( recommend you don't go that hot - especially because the PTFE in your print head ages faster).  I do these changes live in the TUNE menu as soon as it starts printing.  If I have to do it everytime it is more annoying and motivates me to change the PTFE sooner (hopefully).

     

    How hold is your printer?  When did you last change the PTFE?  You should change it every 500 to 1000 hours of printing (depending how hot).

     

    I think Ultimaker calls it the "isolator" maybe?  You can get them from Ultimaker at a really decent price or from 3rd party sellers like 3dsolex.com.  I sell them for people in USA.

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    Posted · Gaps in circles

    Hi gr5,

    thanks for your support, I really appreciate that.!
    I don't know exactly how old my UM2 is, I guess somewhat 4 years.
    The PTFE I changed maybe 3 years ago when I installed the Olson Block.

    I try your suggestions now...

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    Posted · Gaps in circles

    Hi gr5,

    I tried your suggestions now and it seems the print is better now.
     

    Just to improve my knowledge, what has the PTFE coupler to do with underextrusion please?
    What is the relationship between both?

    Thanks...
     

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    Posted · Gaps in circles

    PTFE is teflon and teflon doesn't do well above about 200C.  The teflon in the Ultimaker is a version that works pretty well up to 220C but still it degrades after about 1000 hours of printing at 200C and degrades faster at 220C and even faster at 240C.

     

    What happens is the teflon gets soft.  It only degrades at the very bottom where it touches the heater block.

     

    When it gets soft, and combined with pressure above - from the spring (or if you have a UM2+ from the aluminum cylinder) and also pressure from the bowden if you tighten the bowden too much - what happens is it compresses and squeezes the filament.  A LOT!   The PTFE tries to collapse (at the base/bottom of the PTFE part where it has degraded).

     

    If you remove the filament, remove the nozzle, let the block cool below 50C and then slide filament back through the print head you can feel the resistance of the filament through the print head.  The feeder on the original UM2 can only push with about 5 pounds of force and UM2+ with about 10 pounds of force (5kg).  The resistance from the PTFE alone can add about 2 pounds of resistance when it is time to change it.  That can be half your budget!  Plus when you push hard you get additional resistance at the top of the bowden and can add another pound of resistance.  This can take up now 3/4 of your budget!  Not much leftover for printing nice parts fast.

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    Posted · Gaps in circles

    Hi Gr5,

    thanks for your detailed reply!
    With the PTFE coupler I understand now, so I will replace it.

    But this part I do not understand:
     

    Quote

    Plus when you push hard you get additional resistance at the top of the bowden and can add another pound of resistance.  This can take up now 3/4 of your budget!  Not much leftover for printing nice parts fast.


    Could you explain more simple pelase?
    Is there anything further to do (with the top of the bowden) to improve my prints?

    Thanks again...

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    Posted · Gaps in circles

    The inside of the teflon gets really burnt and worn-out: it severely deforms over time. So the material gets stuck in it when doing retractions.

     

    You can see the deformations when doing a cold pull.

     

    The orange cone at the bottom is what a good teflon coupler looks like on the inside (the other cones were pulled-out too soon, before the material was solid). It mirrors the inside of the coupler and of the nozzle.

    DSCN5238.thumb.JPG.511ef26080bf76c822b2a2dba0241153.JPG

     

    The white cone at the bottom shows a thick ring, just inside the teflon coupler (where the teflon coupler was before pulling the filament out). That thick ring is where the teflon coupler is damaged inside. So during a retraction while printing, the hot melt is pulled upwards into the teflon, cools down, solidifies, and then gets stuck and can't move forward easily. It is due to the pressure of the hot melt against the side-wall, when pushing forward again after a retraction, that the teflon coupler is slowly damaged due to the heat and pressure. So, less heat and less retractions, mean less damage. If I understood everything well, that is...

    DSCN5237.thumb.JPG.8f29c03aad2ce9dd0d9490ed2ece9d98.JPG

     

     

     

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    Posted · Gaps in circles
    21 hours ago, 3dnerd said:

    Plus when you push hard you get additional resistance at the top of the bowden and can add another pound of resistance.  This can take up now 3/4 of your budget!  Not much leftover for printing nice parts fast.

    The feeder is pushing hard on the filament upwards into the bowden.  Typically with 2-5 pounds of force.  The hot end is at high pressure and so pushing back with a similar force.  These 2 forces combined are both pushing upwards.

     

    Sometimes this upward force can push the bowden right out of the printer.  But normally not.

     

    Still the filament is pushing up mostly near the top of the arc of the bowden.  Quite hard.  Typically 4-10 pounds of force.  Enough to lift the printer up into the air if the forces weren't also pushing down on the printer.

     

    So the filament is rubbing against the bowden.  This causes friction.  The bowden itself can get old and rough on the inside.  It's good to replace the bowden.  Maybe very 1000 to 3000 hours of printing (once every year for a printer used 8 hours every day).  Even if the bowden is perfectly new this extra friction is part of your budget.  When you use up all the budget the feeder stepper skips back a step or the filament simply slips through the feeder and you get underextrusion.

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