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Most of my part is printing very well, but I have problems in the bottom layer and in layers that are the first layers, but not necessarily layer 0.

Looking at the print quality troubleshooting, I can't find a problem that fits my needs. Using the terms over there, I would describe it as "gaps in bottom layer".

Photo from part A (RPi case top piece):

rough and sunken

Photos from part B (RPi case bottom):

There is a really ugly screwhole (sorry for the blurry picture):

Ugly screwhole

But in the same part, there's an almost perfect much better screwhole:

Perfect screwhole

For the location on the print bed, it's here (both parts):

Problematic region

I have seen the question First bottom layer has gaps, where the OP has already tried a lot.

My thoughts so far:

  • I don't want to generally lower the Z height, since it prints fine over a large area with a really flat and smooth surface.
  • I'm not sure I should change the temperature settings. I use the i3 MK3 printer and I use Prusa PLA filament with Slic3r Prusa PLA filament settings.
  • I don't understand many of the extrusion width / extrusion multiplier options of that question.
  • I thought I might have had a fingerprint on the print plate. I typically avoid that by wearing gloves and cleaning the print bed with alcohol every fifth print or so. However, I didn't clean before any of the two parts. (I cleaned now)

Given the description and the pictures, can you name the problem and suggest the most likely solution?

Printer and filament details:

  • Prusa i3 MK3
  • Prusa PLA filament 1.75 mm, pearl blue
  • 0.20 mm SPEED setting
  • 20% infill
  • 5mm Brim
  • 215°C first layer, 210°C other layers
  • 60°C bed temperature
  • Prusa PLA default filament settings

I use a Prusa spring steel print bed. No special adhesion, tape or anything. Closest I could find in the shop is smooth PEI, but mine looks more golden.

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  • $\begingroup$ do you have adhesion issues too? $\endgroup$
    – kolosy
    Apr 16, 2019 at 19:54
  • $\begingroup$ You print pretty hot, and the gaps between the deposited filament lines give the impression that the nozzle is not close enough to the bed for the first layer. What type of adhesion on the bed are you using? Please update the question. $\endgroup$
    – 0scar ♦
    Apr 16, 2019 at 20:00
  • $\begingroup$ Agree with @0scar on the heat. Also, even on the "good screw hole" it appears there are irregularities. In the image, at 10 O'Clock of the screw hole, it is rather squished, while directly across at 4 O'Clock (and above it on the longer passes), the extrusion is quite a bit longer and thinner, with some gaps showing. It just doesn't look equal as I'd expect. Maybe I'm out in the weeds and the image doesn't do it justice, so just kinda throwing this out there. $\endgroup$
    – Pᴀᴜʟsᴛᴇʀ2
    Apr 16, 2019 at 20:07
  • $\begingroup$ @Pᴀᴜʟsᴛᴇʀ2: that's true. It's flatter and smoother when the lines are shorter, such as in the squished area. It's thinner on long lines. This would mean that I could try to lower the speed of type "solid infill" (pink in Slic3r) like I did for PETG. Maybe I should apply that for all presets. $\endgroup$
    – Thomas Weller
    Apr 16, 2019 at 22:12
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    $\begingroup$ @0scar: I printed 2 more pieces and yes, maybe I have adhesion issues. I didn't notice it, but the objects go off the steel spring plate a bit too easily. It seems one really needs good senses and a good memory for how the objects stick to the plate. I also changed the filament type. It's the first time I printed with this filament type and color, so maybe I underestimated the importance of things like stickyness. $\endgroup$
    – Thomas Weller
    Apr 16, 2019 at 22:35

2 Answers 2

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I know you said you don't want to change the Z height, but it does look like you're printing a bit too far from the plate. I would recommend adjusting your Z-offset if you can, or adjusting the limit switch (or whatever your Z-homing mechanism is)

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    $\begingroup$ The variation in print makes an unlevel bed suspect, i.e. wrong Z height in only one area. $\endgroup$
    – Perry Webb
    Apr 16, 2019 at 21:23
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    $\begingroup$ @PerryWebbp Indeed, level is the key here, it looks like the bed is not properly levelled or that tape is incorrectly placed. $\endgroup$
    – 0scar ♦
    Apr 16, 2019 at 21:55
  • $\begingroup$ Add the levelling bed to your answer to be valid :), now is the half of the answer. $\endgroup$
    – Fernando Baltazar
    Sep 17, 2019 at 4:21
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Definitely the corner of your bed where print was worse is slightly unleveled (a little too low), because if you look the hole, it has artifacts too, probably because the nozzle was depositing the melted filament from a higher distance than on the "good" part.

You can see later in that hole, that the layers finally catch up with the rest, so:

  • You need to correct the bed leveling on that corner (too low)

Also, the better part doesn't look right either. You can see the ring around the good hole doesn't close because the filament din't stick at the beginning of the circular movement. Plus, your first layer should be smoother than that, not wormy-like.

To experiment how to get a better first layer you need to tweak in very small amounts:

  • The first layer height (I may need to be lower for you)
  • The temperature (I don't think you need more temp for your first layer, probably the fans start blowing after the second layer anyways)
  • The % of extruded material (you may increase it in very small amounts only for the first layer [and only after a lower layer height didn't worked])
  • The speed of the first layer (it may need to be lower. imagine your nozzle is trying to print with chewing gum and what would happen if speeds are too high, PLA has a rubbery consistency when melted)

Also:

  • Be sure the surface is clean

Dust and oils from manipulation on certain spots can cause the filament not to stick, even when you think is clean. I use alcohol when printing on a bare surface, change the masking tape, or use just a paper towel (when I'm using PEI sheet)

If that doesn't give you a a better first layer, but it is at least even, you will need to adjust your z-axis offset or level the entire bed up a little.

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