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I've only been 3D printing for a few weeks and most of my prints seem to come out fine, but when I try to print models which require a small clearance between sections of the model, e.g. various tolerance/clearance tests and some others, I can't get them to separate when they should because the bottom layer is a solid plate with no gaps.

For most models, this seems a good feature as they stick well and the final surface is completely flat, but for some, I want parts to be separable, so there should be some clearance on the first layer..

From some research, I suspect it may be either that the nozzle is too close to the bed or that the bed (or nozzle?) temperature is too high.

I have an Ender-3 and use PLA with a 200 °C nozzle temp and 60 °C bed temp. When leveling, I've been using a post-it note to set the nozzle clearance. I've tried dropping the bed temp to 45 °C and even 30 °C, but this didn't change the first layer printing of the Maker's Muse tolerance test, which still came out with a completely solid first layer and hence was basically a brick! I also tried using a raft, but the result was that the raft couldn't be removed from the model so this changed nothing.

What should I try to improve this?

Some details:

I'm using CURA 4.4.1 with as far as I can tell mostly default settings. I've tried the profiles Standard Quailty 0.2 mm and Super Quality 0.12 mm but this doesn't change things. FYI, as you might guess, I haven't changed the default nozzle so it's 0.4 mm.

The main reason for the question is that I don't know where to start with adjusting the settings, so had hoped someone would ask for the value of specific settings rather, than a full lisy, since most of the seem to do with the structural integrity of the body and shell of the model rather than the base, but here goes... 

Shell:
    Wall Thickness: 1.2 mm
    Wall Line Count: 3
    Top/Bottom Thickness: 0.8 mm
        Top Thickness: 0.8 mm
        Top Layers: 4
        Bottom Thickness: 0.8 mm
        Bottom Layers: 4
    Horizontal Expansion: 0 mm

Infill:
    Infill Density: 20 %
    Infill Pattern: Cubic

Material:
    Printing Temperature: 200 °C
    Build Plate Temperature: 60 °C
    Flow: 100 %
        Wall Flow: 100 %
        Outer Wall Flow: 100 %
        Inner Wall Flow: 100 %
        Top/Bottom Flow: 100 %
        Infill Flow: 100 %
        Skirt/Brim Flow: 100 %
        Prime Tower Flow: 100 %
        Initial Layer Flow: 100%
    Enable Retraction: [Yes]

Speed:
    Print Speed: 50 mm/s
    Travel Speed: 150 mm/s
    Initial Layer Speed: 20 mm/s
    Initial Layer Print Speed: 20 mm/s
    Initial Layer Travel Speed: 100 mm/s

Travel:
    Avoid Printed Parts When Traveling: [Yes]
    Avoid Supports When Traveling: [On]
    Travel Avoid Distance: 0.625 mm
    Z Hop When Retracted: [No]

Cooling:
    Enable Print Cooling: [Yes]
    Fan Speed: 100%

Support:
    Generate Support: [No]

Build Plate Adhesion:
    Build Plate Adhesion Type: Skirt

Dual Extrusion:
(No settings - single nozzle)

Experimental:
    Tree Support: [No]

Printer Settings:
    X(Width): 235 mm
    Y(Depth): 235 mm
    Z(Height): 250 mm
    Build Plate shape: Rectangular
    Origin at Center: [No]
    Heated Bed: [Yes]
    Heated Build Volume: [No]
    G-Code flavor: Marlin

Printhead Settings:
    X min: -25 mm
    Y min: -32 mm
    X max: 32 mm
    Y max: 34 mm
    Gantry Height: 25 mm
    Number of Extruders: 1

Start G-code:

    M201 X500.00 Y500.00 Z100.00 E5000.00 ;Setup machine max acceleration
    M203 X500.00 Y500.00 Z10.00 E50.00 ;Setup machine max feedrate
    M204 P500.00 R1000.00 T500.00 ;Setup Print/Retract/Travel acceleration
    M205 X8.00 Y8.00 Z0.40 E5.00 ;Setup Jerk
    M220 S100 ;Reset Feedrate
    M221 S100 ;Reset Flowrate

End G-code:

    G1 E-2 F2700 ;Retract a bit
    G1 E-2 Z0.2 F2400 ;Retract and raise Z
    G1 X5 Y5 F3000 ;Wipe out
    G1 Z10 ;Raise Z more
    G90 ;Absolute positionning

Material is Generic PLA:
    Default Printing Temperature: 200 °C
    Default Build Plate Temperature: 60 °C
    Retraction Distance: 6.5 mm
    Retraction Speed: 25 mm/s
    Standby Temperature: 175 °C
    Fan Speed: 100 %

Standard Quality Settings:
    Quality:
        Layer Height: 0.2 mm
        Initial Layer Height: 0.2 mm
    Shell:
        Wall Thickness: Calculated
        Top/Bottom Thickness: Calculated
    Support:
        Support interface Thickness: Calculated

Super Quality Settings:
    Quality:
        Layer Height: 0.12 mm
        Initial Layer Height: 0.2 mm
    Shell:
        Wall Thickness: Calculated
        Top/Bottom Thickness: Calculated
    Support:
        Support interface Thickness: Calculated

As you may already know, there are lots of other settings which, by default, are not visible. If you need the value of one of these, I'll turn it on and see what it is.

I've also got a few of the failed pieces out of my junk box and added a couple of photos/ As you can see, the underside is beautifully flat and solid.

Makers' Muse tests undersidetop

I also tried this test, but the only reason I got one of the pegs out was it broke off the base layer!

FDM test V4underside

Update2:

Results of trying to increase spacing when levelling. Spaghetti

Update3:

Not an answer to the original issue, but I found a workaround in that there is an option in CURA to turn off the "drop model to build plate" option, so the whole model can be made on supports. This then doesn't have a 'solid' first layer and I get a test piece which shows I can print down to a separation of 0.2mm and have the parts remain free; 0.15 doesn't free up.

Old, new and support

Original attempt, new version and the support.

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  • $\begingroup$ PostIts are listed as 30-thousands of an inch, so 76.2 µm, about 3/4 of the 100 µm that we aim for. $\endgroup$ – Trish Feb 26 '20 at 19:34
  • $\begingroup$ What weight of paper is recommended? Most people just seem to say "a piece of paper". I have either 80 g/m² or 120 g/m², both A4. $\endgroup$ – StarNamer Feb 26 '20 at 22:22
  • $\begingroup$ Your settings show adhesion is set to skirt, but the first print looks like it was done with a brim or something... $\endgroup$ – R.. GitHub STOP HELPING ICE Feb 26 '20 at 23:44
  • $\begingroup$ @R..GitHubSTOP I HELPINGICE I mentioned in the question that I tried using a raft. The samples in the picture include that case. $\endgroup$ – StarNamer Feb 27 '20 at 8:35
  • $\begingroup$ If that's a raft, it looks like you broke/cut away the parts of the raft not under the print rather than separating the raft from the print. Was it bonded so that it couldn't be separated? $\endgroup$ – R.. GitHub STOP HELPING ICE Feb 27 '20 at 15:09
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The overall flow rate seems ok -- I see a nice gap in the 0.2 mm peg case.

The most likely problem is the first layer is too thin, or to much material is being over extruded.

I don't know Cura as a slicer. It may have an option to over-extrude the first layer. Unless I found such a parameter, I would look at how z=0 is set.

Just add an experiment, try using 3 Post-It notes. How, if at all, does the result change? Do you still have adequate bed adhesion?

If you can make the first layer thicker, it might be relatively closer to the actual thickness. Can you program a 0.35 mm first layer?

If you can't make the first layer thicker, maybe try setting all the layers to be thick. It might not handle the overhang as well, but today's question is about the first layer expansion

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  • $\begingroup$ Last night I tried using a piece of 80 g/m² A4 paper and setting the height so the "tension" felt when moving the paper with the nozzle at Z=0 was slightly less than I've been doing previously and, after watching the first couple of layers, left the printer working on a couple of boxes overnight, as I've down over a dozen times before. This morning I came down to my first example of "spaghetti". Measuring the partial model that printed, it looks like part of the model detached from the bed around layers 8 or 9 out of 70. Obviously, I've gone too high and need to reduce! $\endgroup$ – StarNamer Feb 27 '20 at 8:43
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    $\begingroup$ uhm, spaghetti at layer 10 means something else is afoot probably... $\endgroup$ – Trish Feb 27 '20 at 11:28
  • $\begingroup$ Spaghetti is a good meal but a terrible print. An 80 g/m^2 paper should not have been too thick. Perhaps you have a bed adhesion problem that was masked by a high first-layer squish? $\endgroup$ – cmm Feb 27 '20 at 12:41
  • $\begingroup$ As I said, this is the first time I've either got spaghetti or model separation after the initial layer. I've usually stopped the print if either the skirt or the initial layer doesn't stick. So when I used a thicker piece of paper and allowed less "tension" against the nozzle at Z=0, I watched it produce the first and 2nd layers then assumed it would be OK. $\endgroup$ – StarNamer Feb 27 '20 at 21:42
  • $\begingroup$ At least I've identified a possible reason for the spaghetti ... The hot end cooling fan had stopped. Voltage on the board seems OK, so I assume it's the fan and have ordered a replacement. I've also had to replace the Bowden tube as the PLA had melted inside the tube, presumably because the heat sink got hot, and, when I tried to retract it, it got stuck partway up the tube. $\endgroup$ – StarNamer Feb 28 '20 at 11:50

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