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Dimensional weirdness of my Prusa Mini+  

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MD3D
 MD3D
(@md3d)
New Member
Dimensional weirdness of my Prusa Mini+

Hi everyone,

i do not know how to proceed further. I spent now two weeks in trying to get dimensional correctness from my Prusa Mini+, which is three weeks old. If i just use standard settings, everything printed is slightly too small (~0,5mm off). So outer and inner distances are all off. My fist thought was that the filament was the issue and after that i suspected my Mini was configured wrong.

I asked my beloved teacher youtube and followed three (Video1 Video2 Video3) videos i could find for calibrating and setting up my Mini correctly but nothing worked. I now own approximately 15 calibration cubes which are all not within 0,1mm in dimensions AND have a decent appearance. I will now list all the parameters that i changed and the effekt maybe you can help me where i made the mistake. I started with an all stock Prusa Mini+ with the newest firmware and Generic PLA filamentprofile:

  1. Filament diameter: i checked with my calliper ten spots on my filament and created an average diameter which i set to PrusaSlicer
  2. First layer thickness: adjusted it to print the Mini's first layer test to be exactly 0,2mm and confirmed this with a single layer print covering almost the entire printbed
  3. Extrusion width: if i print the cube in vase-mode and just one outer wall (all other lines were set to 0,45mm in PrusaSlicer to be sure) i get 0,4mm wall-thickness. so my extrusionfactor would be 0,45/0,4=1,125. This was set to PrusaSlicer
  4. XYZ-Dimension: printing the xyz-cube 20x20x20mm i get almost perfect dimensions in x and y. but on z i have 0,33mm to much and this is cause by massively overextruding and this is also my only constant i get after all this.

Of course i checkt all the other things during my iterations. Checked all the bolts. Checked other Filament. Checked with other slicer. Checked E-Steps and adjusted those on all four motors. Checked different .stl-files.

nothing changes. i get pretty but slightly too small prints or i get the correct measurements but super ugly corners and top-layer. I did not even check the effects of bigger prints since i get all those things already in the small ones.

Anybody with an advice what i did wrong or what i did not check? would really appreciate it! If i forgot to include any information in this post let me know.

THX

 

 

 

Posted : 18/03/2022 7:03 pm
Diem
 Diem
(@diem)
Famed Member

If this is proportional to the dimension then you may just be seeing thermal contraction:  is your printer laying down hot plastic accurately - which then contracts as it cools?

Address this with calibration of your original design. 

There are other minor distortions, most often of curves, caused by triangulation and rational approximation when translating ideal dimensions to practical printer movements.  Trial and error  will usually find an optimal value in a couple of iterations.

And the usual advice applies when making dimensionally critical blanks, build slightly oversize and machine to fit.

Cheerio,

Posted : 19/03/2022 12:40 pm
MD3D
 MD3D
(@md3d)
New Member
Topic starter answered:
RE: Dimensional weirdness of my Prusa Mini+

Hi Diem,

Thx for your reply. I tested your reccomondation and did GEZ the same weired measurements. But now today i had the magic Moment.

 

My calipers were set to increment-mode. According to the handbook this Mode has to be calibrated to be exact and correct, which i never did. Also i never intended to use this mode and i just recognized it today because i accidently hit the button to switch meassurement-mode.

 

Turns out my very first extrusion-width Was exactly 0,45mm and i did Not habe to change an thing! I now thank myself for documenting ever Single step i did during my process. Because now i could easily return to the setting i used back then.

-->of you measure wrong over and over, it may just be your measurement-rool which is wrong.

I can Not belive that i did Not See the icon on my calipers display 😖 

Posted : 25/03/2022 8:00 pm
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