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Wrong scale

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Hi there

In order to test the x-y-accuracy of my new Ultimaker (no modifications so far) I printed a cube with 1cm length at 0.1mm z-resolution (using Cura) in PLA. The results I got were x=9.4mm, y=9.9mm and z=10.2mm. I'm fine with the y-scale, also with the z-scale as I printed a 0.3mm first layer. However, the x-scale seems to be out of range.

I then checked the distances for certain head movements. When driving 150mm in x-direction I got 151.5mm; the same for the y-direction. I adjusted the x- and y-step values and saved them in the EPROM. Checking the driving showed it was ok then. But the cube-print stayed the same, I still got 9.4mm instead of 10mm.

When checking the Ultimaker forum I found a post about shrinking, arguing the shrink in x-direction might be significantly higher due to the fan blowing in that direction. I tested this theory by setting the fan to 25% PWM; it didn't change anything.

I would like to ask the experts among you I they had any idea what might be wrong.

I'm aware I could change the x-scale in Cura for compensation but I'm not looking for a work-around but for a serious solution.

I'm looking forward to your inputs...



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The plastic is shrinking. I doubt the fan makes much difference X versus Y as it blows more on top of the print than a particular side. Plus the shrinking should be exactly equal in X and Y shouldn't it?

Look at your 6 X pulleys. Move the head back and forth. Are the pulleys round? Or do they wobble? Some people have found pulleys with the hole not centered. Other's had the hole so large that when they tightened the set screw the pulley moved to the side. Maybe if you do something that is the same length as the circumference of a pulley (approx 60mm?) it will be more accurate? Just some thoughts.

Usually people who really care about a dimension design something in CAD, print it, then adjust by the error and print again. It seems crazy but that's also how most people do it with word documents (print everything twice). And it works as the printer may be off a bit due to shrinkage but it's pretty consistent if you print with the same settings and with the same PLA and with the same air temp etc.


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Thanks a lot for your help. I checked they pulleys; they show a very slight wobble which seems to origin from the natural play they have on the axis. But when checking I found the x-motor not fixed very vell to the back plane and the front x-belt being not as tight as the back belt and as it should be. After having fixed these two issues, I get quite accurate prints (9.8mm when 10mm in the model, 100.0mm when 100mm in the model, 30.5mm when 30.6mm in the model, etc...) even when printing with 150mm/s!


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PLA will always shrink a tiny bit !!

I just modelled very accuartly a replacement part for some tubberwear and it came out about... 03mm too small

you can either just print with a tiny bit more meat where you need it or just accept the nature of PLA.

Best wishes.

Ian :-)


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