ultimaker 3 not printing correct size

[Arjan210299 0]

6 months ago i printed a calibration cube that is 20x 20x20 and it was exactly 20x20x20. when i print it now it is 20,3 in the x 20,1 in the y and 20 in the Z i printed the cube multiple times with the exact same results so that should rule out backlash from the belts. just for good measure i re tightened  the short belts but with no change. does anybody know why 

[Smithy 1,145]

It mostly depends on the material, speed, print temperature and so on....

 

So print as cool as possible and not faster than 35mm/sec. It also helps to equalize all the speeds to the same value. Search the forum here for dimensional accuracy and you will find some posts with the relevant settings.

[Arjan210299 0]

so i should change the standard settings for the ultimaker pla ?  and it is accurate but not the same as the file. if iprint the part multiple times it is always the same in dimensions it is just not the correct dimension

[Smithy 1,145]

Yes, try these settings:

 

Line Width: 0.4 (all line widths 0.4)

Wall Thickness: 1.2

Wall Line Count: 3

Top/Bottom Thickness: 1.2

Print Speed: 30

  Infill Speed: 30

  Wall Speed: 30

  Outer Wall Speed: 30

  Inner Wall Speed: 30

  Top/Bottom Speed: 30

Print Jerk: 30

  Infill Jerk: 30

  Wall Jerk: 30

  Outer Wall Jerk: 30

  Inner Wall Jerk: 30

  Top/Bottom Jerk: 30

Horizontal Expansion: -0.03 

 

These settings can also help:

Outer Before Inner Walls = checked

Combing Mode = off

Slicing Tolerance = Exclude