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Unanswered Robo Calibration for tight part fitment!

Discussion in 'Troubleshooting' started by zenekNY, Mar 5, 2016.

  1. zenekNY

    zenekNY Member

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    Hello everyone! I need help with my Robo, :mad: I started working on putting together a little laser engraver which uses DVD drive mechanisms to move object and laser around. Very cool project!http://www.thingiverse.com/thing:902826 . After printing all parts out it turns out that none of the parts fit together. But that's only in my case, it works great for everyone else. I've read up on it a little bit and it has something to do with the shell thickness and XY ratio or whatever. I spent hours filing the parts to get them to fit and I thought that instead of dealing with the problem it's time to solve it! Did anyone of you encounter such problem? It looks like everything relating to Z the axis is alright, but the wall thickness is larger that I want it to be. Distances between holes and etc. are alright, only the walls are too thick. They're nice and smooth after z rod upgrade and extruder calibration.
     
  2. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Several things contribute to making parts that are dimensionally accurate. Extrusion width is controlled by extrusion multiplier, some slicers will allow adjustments to X/Y dimensions to adjust for holes fitting properly (Slic3r has this feature, I think S3d does also). First thing is that your printer be calibrated properly, then with a properly calibrated printer as a base, all these other adjustments are easier.
     
  3. zenekNY

    zenekNY Member

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    Until now I thought that my printer was calibrated. I mean, I successfully printed the 20x20x10 cube with spot on measurements +\- 0.05mm, calibrated the extruder, got the right temperature for the filament and I got rid of the z ribbing.

    Speaking of the slic3r, where is this feature located? I'm using cura for the last few months, I don't know if there is any way to change that setting in cura. Neither is using other slicer than cura's in cura software, is it?


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  4. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Did you print the test models out of the same filament you are printing now?
    All filament can be slightly different when printed and over the course of printing a larger model the errors can be additive.
     
  6. zenekNY

    zenekNY Member

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    They were all PLA, same manufacturer but different colors


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  7. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Well, always test every spool if the requirements you have are tight.
    How far out of tolerance were the larger parts? See if you can measure them and tell.
    For most models out there it doesn't take a large variance to make the difference.
    If you do your own models you can adjust them for the specs you know your printer delivers.
     
  8. zenekNY

    zenekNY Member

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    Approximately 0.35mm too tight on most of the parts.


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  9. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Not bad for a part of any real size. What percentage error does that work out to?
    You original was 0.25% which is certainly reasonable for this type of printer.
    If these other parts are exceeding that then there may be something to chase.

    Normally the accuracy can be measured in hundredths of an inch, but this can often be additive (for example ± 0.005 inch per layer or shell could continuously add up for each layer or shell).

    In reality what I see is that the errors tend to be inconsistent (+0.005 on one, -0.005 on another) so that the average error is still rather decent. Not shocking given the style of printer and design. This is not an ultra-high precision machine, but can do remarkably well for the cost.

    You need to allow for some 'slop' in your models. For loose fit we leave more room and for a tight fit we add more shells for sanding.

    Alternatively slow everything down (print speed wise). That will help increase your accuracy.
     
  10. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Geof likes this.
  11. zenekNY

    zenekNY Member

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    don't get me wrong, I love my Robo and I'm very happy with how it prints, it just seems that for whatever reason the walls are thicker than what they're supposed to be. I'm looking for rather a software solution that would help me loose that 0.175mm on each wall, given a light error on both parts and the tolerance that was counted for by the designer is lost. The sides of the prints are very smooth and consistent. Probably if I owned the software I'd be able to increase the tolerances but I don't have any CAD software that would allow me to edit the project.
     
  12. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    If you are printing other folks models you are at the mercy of it being tried and tested printable :)

    Likely you can tighten up the tolerances with some adjustments to the printer software side.
    Not sure what you are printing with, that might help direct you to where to look for more ideas.
     
  13. zenekNY

    zenekNY Member

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    for the last few months I was using Cura, I'm not really familiar with any other software. I used matter control for a day or two but it didn't work for me.
     
  14. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    We have some Cura users on here, one of them can chime in with ideas.
    You might just try another slicer (say Repetier host w/Slic3r) to see if the error is the same.
     
  15. woferry

    woferry Member

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    I use Cura (15.04.4), could never get MatterControl 1.4 to even launch without crashing and wasn't that happy with Slic3r 1.2.9 when I tried it (lots more controls, but couldn't get the quality as good a Cura was with much less tweaking).

    WIth my R1+Plus I found the outer dimensions were dead-on, X Y and Z (I printed a 100x100x100 calibration axis from Thingiverse and every axis was within 0.1mm on my calipers). However inside dimensions are an issue, so things like making a peg to fit in a hole was tricky. My experimentation has shown that with the 0.4mm nozzle at least, I basically have to subtract 0.4mm from the diameter of a peg (or add 0.4mm to the hole diameter) to get it to fit. This goes for any shape peg I tried, circular, square and triangular. Same for screw holes as well (I used the "polyhole" concept in OpenSCAD, but still had to do an extra 0.4mm adjustment to get the holes to be the proper size). With the combination of polyhole and a 0.4mm adjustment I was able to print every hole size from 5/64" to 3/8" and fit my entire drill bit set perfectly into each hole. My test print was able to be oriented with the holes vertical, horizontal and at a 45° angle and the fit was right in every case.

    I'm assuming the 0.4mm adjustment on the 0.4mm filament width isn't a coincidence, and if I printed with a different nozzle size I'd have to adjust the peg/hole size adjustment the same amount, though I haven't tried changing nozzles yet. It seems that Cura just doesn't make the adjustment for inside dimensions vs. outside dimensions on its own, where it sounds like other slicers can. But the amount it was off by appeared to be the width of the nozzle at least in all of my testing. Or perhaps more specifically half the nozzle width on each side, so assuming the opening is a full surround it's a full nozzle width expansion from wall-to-wall.
     
  16. zenekNY

    zenekNY Member

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    I think that 0.4mm is just a coincidence, but I don't undermine your opinion, maybe there's some connection between these. Perhaps the software generates an extra perimeter or something that is the width of the nozzle. I wish I was able to edit the files to change the tolerances, but files were generated used some advanced CAD software. I will try running repetier host with slic3r. If I remember right, last time I tried it, I couldn't get the slic3r to slice the file, maybe I didn't set it up right in Repetier Host.


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  17. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Ultimately it is going to the the slicer (@woferry is correct).
     
  18. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    The generalization @woferry makes is just that. It will also depend on the extrusion multiplier as if you push out more plastic at the same layer height, that plastic has to go somewhere. Where it goes is outward. So without having a compensation factor such as Slic3r and Simplify3D have you will need to adjust the dimensions or else just drill out the holes to the correct size. Most slicers will try to automatically calculate the extrusion width but sometimes it just gets it wrong.
     
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  19. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The math.. it burns.


    MathBurns.jpg
     
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  20. Geof

    Geof Volunteer Moderator
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    I print test run then adjust in my slicer(I use simplify) the variance from my model to the sicer. Ex a wedge cube for a machine at work comes out .2+ on one model then I undersize .2 instead of adjusting my day to day settings. Lazy way out I suppose but it works for me :). As far as repeatable.... Well it works for most of the run :).

    We are running a mini production plant, print one qa check, print again if out of spec :)
     

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