TIP Inconsistent Printed Height Variations

Discussion in 'Calibration, Help, and Troubleshooting' started by jet, Aug 16, 2016.

  1. jet

    jet Well-Known Member

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    I'm printing some gauge blocks to set the height of a focusing lens in a Lasersaur. I'm used to the shrinkage and expansion problems with ABS and PLA, so I will print a test cube of N mm then measure what is actually printed and change my model. I'll print at 20mm cube, measure the X, Y, and Z, and discover it's a 20.5 x 20.4 x 20.6 mm cube and adjust my model for that particular media and printer.

    However, I've run in to a really strange problem with Simplify3d, the BigBox, and Edge.

    My 20mm cube measures out at 20.25 x 20.16 x 20.84. X and Y aren't an issue with my gauge, but the Z is off by almost a mm. That seems odd, but when I try printing the smaller 17.3mm test cube, Z is off almost a full mm. My 17.3 cube is 17.36 x 17.41 x 18.3. I've tried printing it at .2 and .19 layer heights from a .40 nozzle and I see the same errors. When I print the actual gauge (STL attached) I get the same error on the gauge, but the 40mm alignment piece is only 40.8mm tall, so the 1mm error isn't repeated.

    Any ideas on where to start debugging this? I've imported the STL in other apps and the heights look correct, so I don't think Rhino isn't f'ing up the STL export.
     

    Attached Files:

  2. Dr Jeep

    Dr Jeep Well-Known Member

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    I'm not on a machine with S3D installed but I'll try slicing this tomorrow and check what i get.
     
  3. jet

    jet Well-Known Member

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    Imported the STL again, this time using the defaults for spoolWorks Edge Fine/Fast and got the same results. 17.35 x 17.40 x 18.3.

    I'm going to try and file a bug with S3D but their forum/support has a lot of filtering.
     
  4. jet

    jet Well-Known Member

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    I had Shapeways do a test print and it came back the correct height. I'm leaning towards a S3D bug where 17.3 divided by layer height results in an incorrect number of layers.
     
  5. mike01hu

    mike01hu Well-Known Member

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    You can check the number of layers in the "Prepare to print - Preview Mode" and select "Preview By Layer" where the layer number will be shown in the left hand end of the status line at the bottom of the screen. The math is simple. :)
     
  6. jet

    jet Well-Known Member

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    Well, it's arithmetic not math :) but I see your point. 88 layers, so 87 * .2mm = 17.4mm, add first layer .9 * .2 and I get 17.58mm, still taller than I want but not 18.3mm. The 18.3mm print over 88 (ignore the first layer) suggests that I'm actually printing layers that are .208mm tall. Maybe I should check my z steppers and verify they're using the right number of steps per mm?
     
    mike01hu likes this.
  7. mike01hu

    mike01hu Well-Known Member

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    That sounds logical too.
     
  8. tohara

    tohara Well-Known Member

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    I tried slicing a 17.3mm cube with 0.2 layer height and 90% first layer and i get as you said total of 88 layers, but the 88th layer is not a print layer, it is just for running back to park.

    Summing this up gives me 17.38mm total height, which tally with the Z-height of the 87th layer in the gcode file.
     
  9. jet

    jet Well-Known Member

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    What are you slicing with? I should probably try slic3r and see how it does.
     
  10. tohara

    tohara Well-Known Member

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    I used S3D
     
  11. tohara

    tohara Well-Known Member

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    Are you using Z-lift in S3D? If so, have you tried a print without? Just to see if this is caused by Z axis skipping steps.
     
  12. jet

    jet Well-Known Member

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    I'm using the default of .25. When I take that out and diff the results it looks like
    each extraction has a relative Z movement, I'll try a print without it and see if there's an accumulation error.


    G1 E-1.5000 F4200
    G1 Z0.430 F360
    G1 X128.761 Y89.351 F6000
    G1 Z0.180 F360
    G1 E1.5000 F4200
     
  13. jet

    jet Well-Known Member

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    Same as before: 17.44 x 17.22 x 18.3.

    Zero response on the S3D forum.
     
  14. tohara

    tohara Well-Known Member

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    Strange, what is the last z-height in your gcode file? When i checked the one i generated it was as i said 17.38. Then it should not be possible to get a part that is 18.3 if the nozzle actually is 17.38 above the bed and you don't have some serious over extrusion.
     
  15. jet

    jet Well-Known Member

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    It's

    M117 Layer 91, Z=17.271

    So here's a test -- the STL file is a very simple cube, only 12 facets. and the vertexes aren't 17.3 as in my cad model, they're "17.309999465942383"

    I made a copy of the STL file, opened it in emacs and did a global replace of the very long float with "17.3", still prints out 18.3 tall.
     
  16. jet

    jet Well-Known Member

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    Octoprint also thinks it should be 17.3 high, I'm wondering if I messed up something by accident when upgrading to RC6.


    Model info

    Model size: 38.74mm × 38.74mm × 17.20mm
    Estimated total print time: 24 minutes
    Estimated layer height: 0.20mm
    Layer count: 87 printed, 176 visited

    Layer info
    Layer number: 87
    Layer height (mm): 17.38
    GCODE commands in layer: 110
    Filament used by layer (Tool 0): 0.00mm
    Filament used by layer (Tool 1): 35.39mm
    Print time for layer: a few seconds
     
  17. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    Hi Jet,

    In the last day or so I've installed Alex's Mesh Bed Levelling Hybrid Pro Titan (rearrange words to suit).

    I've had some strange issues getting repeatability on the levelling but sorted it in the end. I created a grid to cover the bed and although the front to back variation was not perfect, after a few layers it looked decent.


    I went on to print my models but my print is pretty poor. They looked quite a state. I can't get the supports off either, they are well and truly solid. I thought it was an over extrusion issue but I recalibrated the Titan/Filament again today and it looked pretty good. The first layers looked great so I left the print for an hour or so and it still looked good. The estimated time from S3D is 4 hours so I left it again for a couple more hours and came back to find the current layer very messy and the nozzle rumbling across the print. I've seen this before where the print height was greater than the nozzle so I stopped the print and began head scratching......

    I'll photograph the prints tomorrow in daylight but it looks like the z-heights are about 80% of what they should be!

    I also printed a 20mm cube at 0.1mm layer height. It came out at 20.3 x 20.4 x 16.2mm !!!!!

    When the file finished, the display showed z=19.99 on both the xyz readout and the 'Layer 200, z=19.99". The gcode file states z19.99mm for the last layer and so does S3D. I know the display value is only really a text message.

    I checked my steps per mm and they're 400. I measured the z- travel of the bed and when it indicates 100mm it measures 100mm (to within what I can realistically measure).

    The only thing I can think is that something mad is happening with the z-position in the bed levelling correction or something's gone screwy with my firmware installation.

    Maybe Alex can suggest something here, does the levelling correction use steps or mm? I'm just wondering if there is some issue with the corrections for different leadscrew pitches?

    I'm giving up for today but will try a re-print of the cube tomorrow and see if anything has changed.

    Cheers

    Jason
     
  18. mike01hu

    mike01hu Well-Known Member

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    No surprise there! :(
     
  19. jet

    jet Well-Known Member

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    Interesting, set the Primary Layer to .15mm: 17.2 x 17.2 x 17.9
     
  20. jet

    jet Well-Known Member

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    Just checked my Z-height with a sashigane (mm scale) and I'm reading consistent distances between 5 and 200mm on the Z movement in the center of the bed. Will try releveling, maybe something got knocked out of position and my data points are bogus.
     

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