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Answered Normal to lose height on prints?

Discussion in 'Troubleshooting' started by Avrution, Dec 5, 2017.

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  1. Avrution

    Avrution Member

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    I'm not sure if this is just related to the Z axis thread, but I've noticed I am losing about .5mm of height on all prints.

    I have very good adhesion to the bed, but the first layer always "squashes" out a little and maybe that is why the height is off?

    I'm just doing 10mm cubes for testing right now and the sides of the cubes are 9.8-9.9mm while the top to bottom is 9.4-9.5mm. Maybe that is within the margin of error?

    As an aside, I did tests using Simplify3D, Mattercontrol and Cura. Mattercontrol actually ended with a 9.7mm height and the cleanest print, while Simplify3D had a 9.4mm height and the choppiest print. Not a great indicator of what the program does and I'm sure it is just settings.
     
    #1 Avrution, Dec 5, 2017
    Last edited: Dec 5, 2017
  2. Geof

    Geof Volunteer Moderator
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    pictures of your print and of the "squish" please
     
  3. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    And include the Startup GCode script you are using for Simplify3D while you are posting.
     
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  4. Avrution

    Avrution Member

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    I couldn't really get the picture to focus enough. The "squish" is very minor, maybe from the heated bed?

    G28 ; home all axes
    G29 ; probe the bed
    G1 Z5 F5000 ; lift nozzle
    M109 S[extruder0_temperature] ; set the extruder temp and wait
    G1 X0 Y0 ; move to begin wipe
    G1 X20 Z0 F4800 ; wipe
     

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  5. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    All three prints suffer from what is commonly referred to as elephants foot. It is a consequence of how most people insure bed adhesion. You ask the slicer to slice up the model, for example, in 0.20 mm layers but you set your Z Offset so that you squish the first layer by 0.05 mm so layer one is actually 0.15 mm not the 0.20 mm you asked for, so your 10 mm height is actually 9.95 mm instead. If you squish more you get an even more compacted first layer and as a result a short overall height.

    If you slicer allows you to set a specific multiplier for layer one only, use it to extrude enough material to get good bed adhesion. Use Z Offset to get layer one equal to what you asked the slicer to make all your layers. That will help mitigate some of the height discrepancy.

    A second aspect that no one will tell you about is that extruded plastic will shrink when it is cooled. Some plastics shrink a lot (ABS is around 1%+) some not so much (PLA is about 0.5%). But they all do it. Lego, the largest plastics user in the world actually manufactures their own plastic formulas and build in errors in the dimensions of their molds because they know exactly where and how much their ABS will shrink and deform when cooled. It is just how it is with plastic. We have machines and chemical filament formulas that we just have no idea how they will react to the heating and cooling process. We can make generalized assumptions, but we will never know precisely what we will end up with when printed..
     
  6. Avrution

    Avrution Member

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    Elephants foot would exactly describe it. Is it generally better to just ignore it so you get a better adhesion layer or just adjust it?

    I do see in Simplify3D that I can change the first layer height by percentage, not sure about the other two.

    The one with the best print does have Z0.3 in the first line, so does that mean it is already lifting that first layer?
     
  7. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    I don't mess with layer one height percentage, because that throws off the height you ask for. I play with Layer one width, that setting forces more plastic to extrude for that layer, in effect making the width wider or filling in more height. The key is still Z offset, you want it so that if you slice at 0.3 mm it is actually 0.3 mm above the bed.
     
  8. Avrution

    Avrution Member

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    So would this be where the M565 command comes into play?

    The example in the FAQ lists M565 Z-1.0, so would I use Z-0.3?
     
  9. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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  10. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Yes
    No, use the proper Z value. There is a small amount of play between when the nozzle hits the bed and the endstop switch is actually triggered, that is what the Z Offset is for.
     
  11. Avrution

    Avrution Member

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    I'll give this a try and see if I can get this dialed in. I haven't had any adhesion issues, but I did see about the painters tape and glue stick so maybe those will help with the layer.
     
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