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Prints Small, Circles Oblong


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Posted · Prints Small, Circles Oblong

On the surface, this looks straight forward, but allow me to give some history.

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I want to be able to print objects I design, with a +/- 0.5mm dimensional tolerance, and have circles and regularly polygons print with a consistent radius and all lines and angles within the polygon are congruent.


See the photo attached to this post.  About 2 weeks ago circles began printing ever-so-slight out-of-round.


This is a standard S5.  It's about 2 years old, and has around 250hrs of print time on it.  It's always printed small objects smaller than they should be (some times as much as a full mm) but for the most part that's not a problem as long as holes are actually circles or regular polygons since any scale deviance in size can be resolved in the model or with some simple hand tools.


 I asked around and did some reading and most suggested tightening belts or re-calibrating.  I opted for the latter--I'm a bit remiss to do any disassembly on this machine.  I calibrated the Z-axis and got stuck.  The printer would fail to start the XY calibration, complaining about a height difference.  While searching for an answer, I noticed there was a firmware update from 5.8.1 to 5.8.2.  Did that.  

A post on this forum lead me to realize it might be a problem with the lift switch and so I watched that carefully and found it was missing the bracket to flip the switch.  I recalibrated the lift switch and could now print the XY calibration pattern.  


The thing I noticed at this time was that the Y portion is exactly the same size as on the paper calibration print out (in the Y direction), and all the tick marks match up with the numbers on the paper.  The X axis, however, is smaller that the calibration rectangle (in the X direction) and starting at the left-most position (-), gets further away from the numbers as the you look to the right (+).  Still, using this guide it looks like +1 is the way to go, but that doesn't help.


If X and Y adjustments are the same [(0.5, 0.5),(1.0,1.0), or (1.5,1.5)] circles are ovals, and polygons are skewed, but right angles with sides perfectly on the X and Y axis are straight.  If the X adjustment is larger than Y, I get a right angle trapezoid when printing the skirt, but printing a rectangular object prints a perfectly right-angled parallelogram as one would expect.

I've attached a photo of the before changes (before Z calibration) and after changes (current).
Before is Ultimaker White Tough PLA, from extruder 1(AA 0.4); the same setup I've used for a couple years.
Current is Polymaker Teal Polylite PETG (CPE) from extruder 2 (AA 0.4);

  • Z-axis alignment
  • Firmware update
  • Calibrate lift switch
  • Calibrate XY
  • New Filament (first time using non-ultimaker filaments) using settings as recommended by SandervG in this post.



Something I have done has taken me from bad to worse and I'm outside my realm of expertise to resolve it.
I am not concerned about problems with infill or material adhesion at this point.


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    Posted (edited) · Prints Small, Circles Oblong

    This 20x20x20 cm cube comes out pretty well.  X and Z are spot on.  I really couldn't ask for any better precision.  Given the accuracy of those, the measurement for Y surprised me.  If X and Z were off by half of that deviance, I'd call it close enough for FDM.  But this is repeatable.  PLA, Tough PLA, ASA, and this CPE.
    Smaller than 10 cm, and X is smaller than the dimensions in the model.  Larger than 10 cm and X about right, but Y is larger than the model by about 10% of the model's dimension on the Y axis.  Print speed (30mm/s to 60mm/s) does not affect the tolerance by anything my tools can detect.

    Larger circles, hexagons, etc have less noticeable skew, but I attribute that to the woefully inaccurate nature of sight and our brains tendency to normalize what we see.

    Any help with diagnosing this is much appreciated.

    Edited by celadon_one
    Confused my axis, corrected.
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