PLA printings always ~0.22% larger I was trying to print parts for a small CD-ROM drive based plotter based on this thing https://www.thingiverse.com/thing:3521286

But as tolerances are very small and need to match the existing parts, I realized that my printed parts are actually a little bigger, I made a test with a part like this:

   _                          _
 /   \                      /   \
 \  .------------------------. ___
    | [O]________________[O] |  ^
    | |                    | |  |
    | |                    | |  |
    | |                    | |  |
    | |  |&lt;--- 62mm ----&gt;| | |  |
    | |                    | | 70mm
    | |                    | |  |
    | |                    | |  |
    | |                    | |  |
    | |                    | |  |
   _| [O]________________[O] | _v_
 /  '------------------------'  \
 \ _ /                      \ _ /

Side View:

      [X]                [X]
 ___[XXXXXXXXXXXXXXXXXXXXXXXX]____



A squared and mouse-eared frame with two protruding 4mm cubes on each corner with inner distances of 62mm and outer of 70mm between each adjacent cubes.

I discovered that, after measuring many times and averaging distances, my model printed 0.227..% larger.

I've heard of shrinkage factor for ABS or Nylon, and people compensate scaling their models while slicing.

But what about PLA?

Im using:


Anet A8
Stock marlin firmware (not the Anet one)
Flashforge natural PLA 1.75mm
0.4mm Nozzle
0.2mm layer height
0.4mm line width
210ºC extrusion temp
60ºC Bed temp
40mm/s print speed
Fusion 360, Cura 2.7 or 4.3 and Octoprint.


The printed model is pretty flat, has no curvatures or artifacts either.

Would this be an error of constants on my printer a known artifact from PLA?
You are not taking into account die swell.

When printing with a 3D printer hot plastic is forced through a nozzle, which leads to the expansion of the material. The result is, that with 0.4 mm nozzle and 0.4 mm intended line width, the material will actually deposit some fraction of a millimeter wider. In your test case, that is 0.22%. If you'd print a double-sized test piece, I expect 0.11%, and in case of a half-sized 0.44% - in other words, it is a static offset.

Because of this, it is usually better to demand wider lines than the nozzle is, forcing the die swell effect to become negligible in the wider line. I managed this with about 110% of the nozzle width on my machines.

Further Reading: Why is it conventional to set line width &gt; nozzle diameter?