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I'm having problems when printing small parts over big areas.

I'm currently printing quite big casing (~180 mm x 100 mm), which has hexagonal holes on the corners. On the first layer the printer prints, in order:

  • Supports inside the holes,
  • Borders around the holes
  • Border of the whole casing and finally
  • Infill (since it is first layer, infill is solid)

When printing borders around holes, printer's head travels between all holes (so that's around 90 % of the whole bed width), what results in filament oozing and the hole borders being underextruded (sometimes to the point, that filament doesn't stick to the bed).

My setup is CReality3D Ender 3 with Ultimaker Cura 3. Most important settings:

  • Print speed 40 mm/s
  • Nozzle temperature 215 °C
  • Bed temperature 60 °C
  • Retraction on travel turned on
  • Retraction additional prime amount set to 0.05 mm3.
  • Outer walls printed after inner ones

What would help (I guess) is slowing down the print after long travels or priming more filament, but proportionally to the travel distance. There are no such settings in Ultimaker Cura though.

How can I deal with such problem?

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  • $\begingroup$ If you have oozing on long moves, you have it on short moves too - but you don't notice. Please report what happens if you double the advance and retract settings and reprint the same gcode. $\endgroup$ – Davo Apr 23 '19 at 11:10
  • $\begingroup$ It is suggested to tune your printer for oozing, several calibration prints can be found on Thingiverse for instance. $\endgroup$ – 0scar Apr 23 '19 at 14:14
  • $\begingroup$ For the next print I lowered the temperature to 205oC and it seems like it helped a little with eliminating oozing - separated small areas looks better as well. I have two more bigger prints ahead, so I'll monitor the situation. $\endgroup$ – Spook Apr 24 '19 at 8:21
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it seems like retraction issue

i would say you should experiment with

  • retraction length - so it would retract more
  • extra extrusion after retraction - so the printer could put some material before it will start your next hole :)

unfortunately there is no good guide how much it should retract and how much it should additionally extrude as it depends on "all your printing circumstances" but here is my arbitrary list in order of importance

  • filament (density - type and producer)
  • temperature (viscosity - hotter filament flows easier)
  • nozzle diam (as filament escapes easier through big hole ;)
  • heat barrier (cooling efficiency - filament should be cool as long as possible up to (or down to) the nozzle)
  • extruder gearing quality (good coupling makes precise retraction and extra-extrusion)
  • cooling (fan and duct should cool your printing right after it sticks to the surface)

and one more thing worth to mention

usually the first layer is not cooled which makes whole system hotter (so filament flows easier)

you could experiment with it too especially for big printouts

so

  • overextrude first layer AND
  • turn on cooling first layer

it seems like there is a bunch of things you can do to master it :)

good luck - it's definitely manageable

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Set retraction_min_travel to 0. The default value is 1.5 and skips retraction when moving less than 1.5 mm. This leads to serious oozing whenever your print has small travel, which seems likely between the hole walls and the supports inside the holes.

Also, the "custom start gcode" in Cura's Ender 3 configuration seriously over-primes the extruder, possibly making retraction ineffective until the pressure drops. Lowering the E15 and E30 amounts to E9 and E18 improved things a lot for me, especially with flex filament, but also with normal PLA. Printing a skirt or brim would probably be an alternative if you don't feel up to editing that part of the config.

Increasing the retraction amount could also help. You should not need extra prime after travel. It can only help if you've lost material to oozing during travel, and if you have oozing, that's a problem in itself that you need to solve, not paper over by extruding additional material.

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