Still Not Printing Level, Could Rod Length or Delta Radius be wrong?



  • Consistently, my printer will print too close at the towers on the outer rim of the bed and it prints too far from the midpoints between each tower.

    This is repeatable no matter what I tweak. I've re-tensioned the belts tighter, removed NEMA dampers, and remeasured and re-squared everything, rotated the effector to see if tilt changes, swapped out various parts, etc.

    When I measure with receipt paper, I get FSR probe trigger heights of 0.10 to 0.15 pretty consistently, but to even begin to get the printer to level out, I have to add 0.2 to 0.3mm to the towers and take 0.10 away from the midpoints - so I don't think it's an FSR height issue.

    The strange thing is that when I calibrate the printer with 7 factors, it changes the Rod Length to about 310mm and it adds about ~3.5mm (144mm) to the delta radius.

    These changes seem to alter the print pattern in a way that seems like it could be one or the other creating my problem, so I'm not sure if I need to adjust rod length or delta radius manually.

    Does the Delta Radius only print concave or convex towards the towers or will it print concave or convex all the way around the bed if it is wrong?

    Should I slightly alter the rod length and let it auto calibrate the delta radius and see if that starts balancing out the issue?

    The rods are labelled 300.15 and I have swapped an extra set out with them that are also 300.15 and it prints the same.



  • Try calibrating with 6 or 8 factors instead of 7 if you are sure your rod lengths are accurate.



  • Also try a manual calibration using escher 3d least squares http://www.escher3d.com/pages/wizards/wizarddelta.php which is the same algorithm used in RRF to do auto calibration. This way you can validate your probing method. If you get a better calibration consider changing the probe. Unfortunately most probes inductive, capacitative, ir, servo etc.. Work less well than you might expect and yet we rely on the results they give us and scratch our heads as it doesn't add up. A manual calibration (assuming a close starting set of parameters) only usually needs one iteration.


  • administrators

    The steps/mm, rod length and delta radius settings are all related. If the steps/mm setting you are using isn't accurate for your printer, that will throw everything else off. So the first thing to do is to check your steps/mm. Check that all 3 belts have about the same tension, then print cuboids or cylinders and measure the actual height vs. intended height. It's best to print 2 different heights and take the difference, to avoid first layer effects. For example print them 20mm and 120mm high and see how close to 100mm the height difference is. Ideally, print a single part with features 20mm and 120mm high to avoid the possibility of starting from a different Z=0 position. Then adjust the steps/mm ni the ratio (desired height)/(actual height). I've seen it claimed that GT2 belts have to be under a lot of tension to have an accurate 2mm tooth pitch, so you may find your prints slightly short and you need to increase the steps/mm a little.

    When you have done that, try auto calibration with S7 again to see what change in rod length that produces. If you increased the steps/mm, you should find that the increase in rod length is smaller than before.

    Broadly speaking, to avoid the uniform pattern of 3 ridges and 3 valleys that I think you are getting, the product of configured steps/mm and configured rod length has to match the actual value for your printer. To get the overall shape flat instead of convex or concave, the ratio of delta radius to diagonal rod length has to be correct.

    HTH David



  • Well, I snapped a GT2 belt… so I definitely have too much tension on them.

    I'm getting ridges and valleys with the ridges between towers and the valleys under the towers.

    I made a little calibration tower with 10mm square spires of various heights, so I'll start checking that tomorrow.



  • My 20 to 120mm tower measured 99.805 instead of 100. So if my steps per mm are off, it's 80.156 steps instead of 80 steps per mm.

    I replaced my belts with some polyurethane white GT2 that has steel threads running inside the core, so those seem much stiffer.

    I think I'll try clamping my calipers to my printer tower and letting the carriage touch them them and then zero them out and move the carriage up 100mm to open the calipers more and see if the calipers measure 100mm. That might allow me to tension the belts roughly equally before going back to FSR calibration.



  • Those White steel cored belts are not good for a delta the cores work harden and snap.

    Ask me how I know.

    I have a load of it and it will be consigned to the scrap bin

    When the cores break the belt really stretches seen one where the inter tooth gap at that point was around 6 mm



  • Thanks for the input - it's hard to find direct sources from people who've tried it. I'll pick up some of the regular GT2 from SeeMeCNC and then and swap it out when it comes in.



  • Reading this thread I realize that I seem to have exactly the same problem, glad that you opened it!

    There is one factor I read about that could play a role, the height correction for the fsr's on the probing points.

    @dc42:

    What is the order of steps you would propose for fsr adjustments?

    a) print test cube to align steps/mm
    b) check reproducibility of fsr's
    c) find out fsr height adjustments for probing points and add them to bed.g script's probing commands
    d) auto calibration S7
    e) check rod length… what to do if it differs from the 'real' rod length?



  • Re. Steel/pu belt it works with big pulleys but 16 and 20 tooth pulleys do snap the steel cores. Deltas are especially problematic as a small area of belt spends a lot of time around the pulleys.



  • @MiR:

    Reading this thread I realize that I seem to have exactly the same problem, glad that you opened it!

    There is one factor I read about that could play a role, the height correction for the fsr's on the probing points.

    @dc42:

    What is the order of steps you would propose for fsr adjustments?

    a) print test cube to align steps/mm
    b) check reproducibility of fsr's
    c) find out fsr height adjustments for probing points and add them to bed.g script's probing commands
    d) auto calibration S7
    e) check rod length… what to do if it differs from the 'real' rod length?

    If you want to generate this shape in OpenSCAD - you can make a custom calibration circle

    [c]// Calibration "Cylinder" for Delta printer // copy this code into an OpenSCAD file and export as an STL file

    $fn = 36; // you can raise this to 100 or so if you want a smoother curve on your circles

    cylinder_radius = 110;
    cylinder_height = 0.3;
    thickness = 10;

    difference() {
    cylinder(r=cylinder_radius, h=cylinder_height, center=true);
    cylinder(r=cylinder_radius-thickness, h=cylinder_height, center=true);
    }

    cylinder(r=thickness/2, h=cylinder_height, center=true);[/c]

    You could measure your thickness at each part of the circle to see how it compares to something like a 0.3 layer height and raise or lower your FSR probe point in the corresponding area. If the height is too low, add that amount as a negative H value (say H-0.05 to make it 0.05 thicker) or make the H amount more positive to lower the height down slightly.

    I'm getting my middle center point of my bed as a cylinder with roughly 0.18 to 0.22 thickness and it varies depending on which side of the circle it's measured on.

    If I use something like the bed probe file below, it begins to correct the ridges and valleys, but not quite - does your printer seem to do something similar?

    [c]; bed.g file for RepRapFirmware, generated by Escher3D calculator
    ; 7 points, 6 factors, probing radius: 150, probe offset (0, 0)
    G30 P0 X0.00 Y150.00 Z-99999 H-0.2; Z Tower
    G30 P1 X129.90 Y75.00 Z-99999 H-0.05; ZY mid
    G30 P2 X129.90 Y-75.00 Z-99999 H-0.2; Y Tower
    G30 P3 X0.00 Y-150.00 Z-99999 H-0.2; YX mid
    G30 P4 X-129.90 Y-75.00 Z-99999 H-0.05; X Tower
    G30 P5 X-129.90 Y75.00 Z-99999 H-0.2; XZ mid
    G30 P6 X0 Y0 Z-99999 H-0.10 S6
    [/c]


  • administrators

    @MiR:

    Reading this thread I realize that I seem to have exactly the same problem, glad that you opened it!

    There is one factor I read about that could play a role, the height correction for the fsr's on the probing points.

    @dc42:

    What is the order of steps you would propose for fsr adjustments?

    a) print test cube to align steps/mm
    b) check reproducibility of fsr's
    c) find out fsr height adjustments for probing points and add them to bed.g script's probing commands
    d) auto calibration S7
    e) check rod length… what to do if it differs from the 'real' rod length?

    Instead of auto calibration with S7, I suggest S6 initially. Only try S7 if you still get the symmetric valleys/ridges pattern that Saffi reports.

    Whatever diagonal rod length you end up in the firmware config, check a couple of things:

    1. The XY size of prints, bearing in mind that they typically end up a little over sized anyway due to filament swell;

    2. Print grid pattern (or just a noughts and crosses/tic tac toe pattern) that covers the whole bed, and check that the lines are straight.



  • Also, here's a few calibrations on my printer with several points and the same probe height - the software is insistent on making my rod lengths 310 - 312mm. I did double check again with calipers and center to center on the ball joints, it's very close to 300mm and the official measurement is 300.15.

    I'll try to run it again and see if I can get 145mm probe points to hit outside the triangle.

    ; S6 auto-calibration
    M665 L312.888 R145.796 H368.282 B140.0 X-0.103 Y0.106 Z0.000
    M666 X-0.044 Y-0.367 Z0.411 A-0.16 B-0.04

    ; S7 auto-calibration
    M665 L312.863 R145.788 H368.261 B140.0 X-0.070 Y-0.000 Z0.000
    M666 X-0.319 Y-0.387 Z0.706 A-0.07 B0.20

    ; S8 auto-calibration
    M665 L300.150 R141.955 H368.210 B140.0 X-0.107 Y-0.026 Z0.000
    M666 X-0.293 Y-0.397 Z0.690 A-0.07 B0.20

    ; S9 auto-calibration
    M665 L312.888 R145.777 H368.274 B140.0 X-0.090 Y0.116 Z0.000
    M666 X-0.067 Y-0.329 Z0.395 A-0.16 B-0.04



  • Thanks…

    When I do run Mesh Grid Comensation after calibration, will it take the H offsets of the bed probing into account (I guess not) or will points that need more force show up as bed uneveness?


  • administrators

    Saffi, it's occurred to me that your valleys and ridges pattern could just be an effect of the FSRs giving different trigger heights near the towers compared to midway between towers. Ignoring scaling errors, when you print a large circle, do you get a more consistent first layer height when you use L=300.15 and calibrate with S6, or after calibrating with S7?



  • I'm going to check on this, in the mean time though, I redid my probe points with tissue paper (minding that I am not that great with gauging the height feel anyway).

    I am posting all my points below for reference:

    100mm Radius Probe Points
    I just hit the probe macro several times for each one

    // Probe Point
    // G30 P0 X0.00 Y100.00 Z-99999 H-0.149

    Stopped at height -0.137 mm
    Stopped at height -0.112 mm
    Stopped at height -0.175 mm
    Stopped at height -0.162 mm
    Stopped at height -0.100 mm
    Stopped at height -0.125 mm
    Stopped at height -0.162 mm
    Stopped at height -0.137 mm
    Stopped at height -0.125 mm
    Stopped at height -0.150 mm
    Stopped at height -0.150 mm
    Stopped at height -0.137 mm

    // End Z Tower Probe Point

    // Probe Point
    // G30 P1 X86.60 Y50.00 Z-99999 H-0.161

    Stopped at height -0.184 mm
    Stopped at height -0.147 mm
    Stopped at height -0.172 mm
    Stopped at height -0.134 mm
    Stopped at height -0.172 mm
    Stopped at height -0.172 mm
    Stopped at height -0.159 mm
    Stopped at height -0.147 mm
    Stopped at height -0.159 mm
    Stopped at height -0.159 mm
    Stopped at height -0.172 mm
    Stopped at height -0.172 mm
    Stopped at height -0.147 mm
    Stopped at height -0.159 mm

    // End of ZY Mid Probe Point

    // Probe Point
    // G30 P2 X86.60 Y-50.00 Z-99999 H-0.151

    Stopped at height -0.137 mm
    Stopped at height -0.149 mm
    Stopped at height -0.137 mm
    Stopped at height -0.162 mm
    Stopped at height -0.174 mm
    Stopped at height -0.149 mm
    Stopped at height -0.162 mm
    Stopped at height -0.162 mm
    Stopped at height -0.137 mm
    Stopped at height -0.137 mm
    Stopped at height -0.124 mm
    Stopped at height -0.137 mm
    Stopped at height -0.137 mm
    Stopped at height -0.137 mm

    // End Y Tower Probe Point

    // Probe Point
    //G30 P3 X0.00 Y-100.00 Z-99999 H-0.180

    Stopped at height -0.184 mm
    Stopped at height -0.172 mm
    Stopped at height -0.172 mm
    Stopped at height -0.197 mm
    Stopped at height -0.209 mm
    Stopped at height -0.184 mm
    Stopped at height -0.172 mm
    Stopped at height -0.172 mm
    Stopped at height -0.172 mm
    Stopped at height -0.197 mm
    Stopped at height -0.159 mm

    // End XY Mid Probe Point

    // Probe Point
    // G30 P4 X-86.60 Y-50.00 Z-99999 H-0.108

    Stopped at height -0.124 mm
    Stopped at height -0.136 mm
    Stopped at height -0.112 mm
    Stopped at height -0.037 mm
    Stopped at height -0.062 mm
    Stopped at height -0.112 mm
    Stopped at height -0.087 mm
    Stopped at height -0.124 mm
    Stopped at height -0.112 mm
    Stopped at height -0.149 mm
    Stopped at height -0.162 mm
    Stopped at height -0.136 mm
    Stopped at height -0.062 mm

    // End X Tower Probe Point

    // Probe Point
    // G30 P5 X-86.60 Y50.00 Z-99999 H-0.137

    Stopped at height -0.122 mm
    Stopped at height -0.122 mm
    Stopped at height -0.122 mm
    Stopped at height -0.159 mm
    Stopped at height -0.134 mm
    Stopped at height -0.147 mm
    Stopped at height -0.172 mm
    Stopped at height -0.184 mm
    Stopped at height -0.222 mm
    Stopped at height -0.122 mm
    Stopped at height -0.084 mm
    Stopped at height -0.109 mm
    Stopped at height -0.122 mm
    Stopped at height -0.097 mm

    // End XZ Mid Probe Point

    // Probe Point
    // G30 P6 X0 Y0 Z-99999 H-0.143 S6

    Stopped at height -0.145 mm
    Stopped at height -0.132 mm
    Stopped at height -0.120 mm
    Stopped at height -0.157 mm
    Stopped at height -0.170 mm
    Stopped at height -0.195 mm
    Stopped at height -0.132 mm
    Stopped at height -0.170 mm
    Stopped at height -0.182 mm
    Stopped at height -0.170 mm
    Stopped at height -0.107 mm
    Stopped at height -0.107 mm
    Stopped at height -0.082 mm

    // End Middle Probe Point



  • Below is the bed.g file I am using. Still printing ridges and valleys that must vary at least 0.2mm to 0.3mm in layer height based on how the 0.2mm layer is barely sticking and too close to even extrude.

    The barely stick is right at each midpoint as usual and the too close starts as you near the tower with the plastic pressure building up and being extra thick as it exits the tower.

    Also, the S6 yielded the following information:

    ; Delta parameters
    M665 L300.150 R142.640 H367.999 B140.0 X-0.251 Y0.141 Z0.000
    M666 X-0.373 Y-0.157 Z0.530 A0.00 B0.00

    [c]

    ; probe the bed at 100 and 98 mm radius with double probe each spot

    G30 P0 X0.00 Y100.00 Z-99999 H-0.149
    G30 P1 X0.00 Y98.00 Z-99999 H-0.149

    G30 P2 X86.60 Y50.00 Z-99999 H-0.161
    G30 P3 X84.87 Y49.00 Z-99999 H-0.161

    G30 P4 X86.60 Y-50.00 Z-99999 H-0.151
    G30 P5 X84.87 Y-49.00 Z-99999 H-0.151

    G30 P6 X0.00 Y-100.00 Z-99999 H-0.180
    G30 P7 X0.00 Y-98.00 Z-99999 H-0.180

    G30 P8 X-86.60 Y-50.00 Z-99999 H-0.108
    G30 P9 X-84.87 Y-49.00 Z-99999 H-0.108

    G30 P10 X-86.60 Y50.00 Z-99999 H-0.137
    G30 P11 X-84.87 Y49.00 Z-99999 H-0.137

    ; go all the way around and probe the bed at 100mm radius

    G30 P12 X0.00 Y100.00 Z-99999 H-0.149
    G30 P13 X86.60 Y50.00 Z-99999 H-0.161
    G30 P14 X86.60 Y-50.00 Z-99999 H-0.151
    G30 P15 X0.00 Y-100.00 Z-99999 H-0.180
    G30 P16 X-86.60 Y-50.00 Z-99999 H-0.108
    G30 P17 X-86.60 Y50.00 Z-99999 H-0.137

    ; go all the way around and probe the bed at 98mm radius

    G30 P18 X0.00 Y98.00 Z-99999 H-0.149
    G30 P19 X84.87 Y49.00 Z-99999 H-0.161
    G30 P20 X84.87 Y-49.00 Z-99999 H-0.151
    G30 P21 X0.00 Y-98.00 Z-99999 H-0.180
    G30 P22 X-84.87 Y-49.00 Z-99999 H-0.108
    G30 P23 X-84.87 Y49.00 Z-99999 H-0.137

    ; add 3 extra points near the very center

    G30 P24 X0.00 Y10.00 Z-99999 H-0.143
    G30 P25 X8.66 Y-5.00 Z-99999 H-0.143
    G30 P26 X-8.66 Y-5.00 Z-99999 H-0.143

    ; probe the center

    G30 P27 X0 Y0 Z-99999 H-0.143 S6[/c]



  • Alright, printing at the same bed.g file posted except I changed it to S7.

    Calibration Below:

    ; This is a system-generated file - do not edit
    ; Delta parameters
    M665 L312.301 R145.735 H367.910 B140.0 X-0.127 Y0.218 Z0.000
    M666 X-0.361 Y-0.131 Z0.492 A0.00 B0.00

    The print of the outer circle improves in that the variance now between layer heights around the circle only looks to be about 0.05mm or so, which is within the FSR margin of error perhaps.

    So I guess the question is why are the arm measurement wrong?

    The ball cup joints have a diameter of roughly 6.50mm, so the only way the arms could be ~312mm is if somehow the pivot point for the joints is not at the center?



  • So if I measure with a universal FSR height of -0.1mm and do 12 points at 140mm and 12 points at 70mm and a center point, I get the following calibration at S7:

    ; This is a system-generated file - do not edit
    ; Delta parameters
    M665 L310.877 R145.827 H367.975 B140.0 X-0.337 Y0.108 Z0.000
    M666 X-0.311 Y-0.162 Z0.472 A0.00 B0.00

    Then a 0.3mm cylinder height with grid infill with 130% first layer width looks like the following below (the ridges and valleys are non-existant):

    https://imgur.com/a/oqyeS



  • Adding a link to the post below from the SeeMeCNC forums, it looks very helpful as the issue appears to be similar (in modifying the rod lengths, the dimensions might change on printed items, which I have not checked on yet):

    http://forum.seemecnc.com/viewtopic.php?t=11441


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