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I've got one particular print which is causing me problems. I've printed other things without changing the filament or printer, so the problem is at least partially the print itself, which has a lot of supports and unconnected sections. What sorts of things can I do to fix this? I'm printing on an Ender 3 Pro and using Ultimaker Cura for slicing.

I print in PLA at 200 °C. The print bed is set to 40 °C. I use a print cooling fan at 100%. The layer height I set to 0.2 mm, the line width 0.4 mm from the 0.4 mm nozzle. I'm not positive what my print speed was set to, but I think I tried it at the default (50 mm/s infill) and then a second time slower (20-30 mm/s, probably). Regardless, the wall speed was set to half whatever the infill speed is. My retraction is 6.5 mm/off at 25 mm/s.

half-completed spider print

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  • $\begingroup$ @agarza I've added the details I remember, the rest will have to wait until I have more time to pull up the files. They're mostly defaults though, although I did try messing with the speed (slowing it down). Can I see these values if I load the gcode in Cura, or do I need to do something special? $\endgroup$
    – Arcanist Lupus
    Commented Mar 1, 2023 at 15:02
  • $\begingroup$ Some of the G-code will have that information, but some will be set within Cura. $\endgroup$
    – agarza
    Commented Mar 1, 2023 at 15:32
  • $\begingroup$ I suspect the retraction, but it is very hard to guess based on the given information. The raft look okay, then all supports and separate parts printing starts, could be retraction related. $\endgroup$
    – 0scar ♦
    Commented Mar 7, 2023 at 19:46
  • $\begingroup$ @0scar ... I honestly didn't expect this question to be hard to answer. Given that I'm pretty sure that the problem is at least partially related to the geometry of the piece, I assumed that it was something frequently encountered by beginner printers, with a known set of related settings. $\endgroup$
    – Arcanist Lupus
    Commented Mar 7, 2023 at 20:10
  • $\begingroup$ Does your printer begin to "air print" (printing midair without filament coming out)? $\endgroup$
    – stopkillinggames.com
    Commented Mar 8, 2023 at 16:41

2 Answers 2

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I have noticed issues like this to happen for me due to what I mention below. I would check each of these and attempt to further narrow down the problem. It is the nature of 3D printing with how different each print shape, machine, and filament being used are, so it is difficult to provide exact settings advice to fix an issue.

  1. Retraction speed & distance - with the incorrect combination you can cause your printer over time to extrude less at certain layers. The problem compounds over time and becomes apparent on prints that have a lot more retraction steps than others. It is important that any time you change to a new brand or type of filament, you run certain temperature and speed test prints. There are certain models that can be downloaded online on Thingiverse or Printables websites that test for print quality based on differences of retraction speeds, temperature, overhang angle, cooling settings, etc. Teaching Tech (YouTube link), for example, offers a very comprehensive array of tests and procedures for calibrating your printer. I suggest visiting his website.

  2. Bowden tube lubrication - Something like a Capricorn™ tube offers less resistance as the filament is sliding through the tube as compared to the Bowden tube that comes with your printer. Increased friction in the Bowden tube will cause inconsistent extrusion of the filament due to impeding the acceleration and speed as the filament is moving back and forth in the tube. Furthermore, it will exhibit different resistance based on how the filament is resting within the Bowden tube while it is flexing as the print head is moving. Lubricating your filament with a little bit of olive oil every few prints will help in this regard in addition to purchasing a higher quality Bowden tube.

  3. Extruder drive gear tension - the point where your filament is biting into the cogs of the extruder needs to be very tight. The spring on the extruder pulley clamp needs to constantly exert enough pressure for the cogs to really dig into the filament. This is important because if the bite is not good enough, it will cause inconsistent extrusion when rapid accelerations happen such as when retractions occur. It is good practice that every few prints to manually push on the pulleys together as over time the spring will degrade and become weaker.

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    $\begingroup$ Number 3 is tricky, as one can have an extruder gear tension that is high enough to deform the filament and cause excessive friction in the Bowden tube. $\endgroup$
    – fred_dot_u
    Commented Mar 8, 2023 at 21:53
  • $\begingroup$ Accepting this answer due to the calibration link, but wha7ever gets the bounty because their answer was the one I directly used $\endgroup$
    – Arcanist Lupus
    Commented Mar 12, 2023 at 0:00
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6.5 mm retraction seems to be way too high. Try lowering it to 3 mm or even 2 mm. (I have my Ender set to 2 mm).

Disclaimer: My knowledge of this topic is not extensive. Nonetheless, below is what I currently know. Make sure to read the comments below for more info.

One of the most important parameters when deciding on the retraction value is the length of the Bowden tube. The longer the tube, the higher the retraction value should be set. It has to do filament compression as the extruder is pushing filament into a nozzle. The longer the distance between the extruder and nozzle, the more filament there is that can be compressed, therefore, the higher the retraction value you need to set to avoid too much filament coming out of the nozzle.

With all that said, based on my personal experience and the experience of my friends who own this printer, for a stock Ender 3 the value of 5-6 mm retraction is too high. Some of my friends' printers make good prints with retraction set to 3 mm. My printer likes the value of 2 mm better, for whatever reason (I modified the extruder and hot end on my printer, maybe that has to do with it).

3D printers kind of "have personalities" and require tinkering around for you to find out the correct values for your prints. Modifications, filament type, filament brand, and many other things/parameters can and do cause requiring changes to your printing values.

So tinker around and see if lowering retraction values gives you better prints.

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  • $\begingroup$ 6.5 was the classic setting for Ender3-length bowden tubes on firmware without pressure advance. It's also making up for the tube stretch/filament spring compression that pressure advance/linear advance would ideally be compensating for entirely. So if this is running more modern firmware with LA, 6.5 would indeed be way too much. $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Commented Mar 8, 2023 at 17:50
  • $\begingroup$ When calibrating retraction, make sure to use well-dried filament, too. If the filament is wet, you end up getting stringing even when it's the right distance (because the plastic keeps foaming in the nozzle as the water bubbles off), and have to increase the retraction length way too much, to the point that resumption is unreliable and can jam, to get the sringing to go away. $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Commented Mar 8, 2023 at 17:52
  • $\begingroup$ Cura has an option for "Z-hop when retracted" - is that likely to affect my issue (other than reducing the chance that the nozzle whacks the print) $\endgroup$
    – Arcanist Lupus
    Commented Mar 9, 2023 at 6:08
  • $\begingroup$ 30 mm/s print speed, 2mm retraction, 20 mm/s retraction speed, z-hop, mostly solved the problem, although I still had problems in two layers. Print was a disaster anyways, because the supports are too sturdy to easily remove. But I don't know that that's a solvable problem. Also, lots of stringing with these settings. $\endgroup$
    – Arcanist Lupus
    Commented Mar 11, 2023 at 23:38
  • $\begingroup$ @ArcanistLupus If you have too much stringing then try increasing retraction value. $\endgroup$
    – stopkillinggames.com
    Commented Mar 12, 2023 at 22:58

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