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UMO+ Wrong Dimensions in x-Direction

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Just some weeks ago I bought myself a Ultimaker Original + kit and assembled it. It works great with various things where exact dimensions aren't needed. But as I want to use it mainly for printing special parts for engineering, I checked if it prints the right measurements.

I started off with a simple 10x10x10mm cube. After it finished I first checked the height. It was perfect, exactly 10mm. After that I inspected the sides and for the y-direction the measurement wasn't that good, but still acceptable (around 9,93mm). Than I inspected the other side and it was only 9,65mm wide. I suspected some kind of error in the x-direction and therefore I wanted to try another thing.

For the next test I printed this piece for calibration: http://www.thingiverse.com/thing:195604

As before I checked the height first. It was perfect with exact 5cm. Than I inspected the y and x-directions. They should be both 10cm long. Keeping the previous results in mind I expected some major issue in the x-direction. But this time both sides have roughly the same value, 9,963cm in x-direction and 9,955cm in y-direction.

I am totally satisfied with the results for the second test. I know that the material (in this case PLA) shrinks when it cools down and I can live with these small variations, especially as they are nearly the same on both axis.

The problem is the wrong dimension for the x-direction of the first print. As a lot of the parts I want to print are relatively small I want some more accurancy here and as the result for the y-direction is much better I expect some kind of issue with the x-axis. Do you experienced the same problem or have a possible solution for this?

If you are interested in the printing settings:

Temperature: 200°

Heated bed: 70°

Layer height: 0,2mm

Printing speed: 50 mm/s

Nozzle (standard): 0,4mm

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I do not measure everything but some of the engineering stuff requires it. I have never measured a variance of > 30 microns, so better than your figures above. I have seen both 10 microns and indeed 0 variance but of course the resolution and indeed the accuracy of the measuring device come into play. I will assume you have an accurate micrometre with a resolution of at least 10 microns and have received training in how to measure accurately.

I have not done real intense testing on this but I have observed...

The filament can play a part on the accuracy; I do not mean PLA vs ABS vs Nylon etc; I mean a different colour of the same filament from the same manufacturer can have an impact.

Speed can have an impact. I never print at 50mm/s I print at 30mm/s or 20mm/s. You should do some testing and see if you can improve your figures - of course if the accuracy is of concern to you.

I guarantee a tolerance of 50 microns but would be happy to go down to 30 microns if required, although that does depend on the accuracy of the part required on whatever is oriented on the z axis. I would not want to go any lower without doing some serious testing. I have never gone below 50 micron layers except once when I started, I think it was 20 microns and I had trouble with it sticking to the bed. I would hope that now I could overcome that.

I run the extruder at as cooler temp. as possible (no idea if this makes a difference) and fans at 100%.

When the print is finished I walk away for several hours and let the printer enclosure cool down to ambient temp. before removing the part (only if accuracy is important and again no idea if it makes a difference). I am not a materials expert but it seems to me that would reduce any shock to the material).

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Thanks for your reply. Today I tried another 10x10x10mm cube with your advice. I adjusted the print speed to 20mm/s and the temperature to 195°. After the print finished I waited some time till everything cooled down to room temperature.

As before the height was perfect. The width in y-direction was also great this time with 10,05mm. But just like before the width in x-direction is corrupt with only 9,7mm.

As the y-direction shows great results I don't think it is because the material is shrinking too much. Is it maybe a problem with the stepper motor of the x-axis?

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Do you have loose belts? This might have an influence. If you have no stochastic error but a systematic error, you could try to change the stepper value until it fits?

Printing exact geometries is also one of my current issues. The calibration with the test object is ok, but unfortunately it will not completely solve the issue. Since shrinkage is dependent on the geomtry of the piece to print, try and error unfortunately can't be avoided. If you have a solution, please let me know.;)

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Today I finally found and fixed the problem. After trying out various things I noticed that the all of my pulley are wobbling like crazy. Therefore I have done an upgrade to GT2 pulleys and belts which was the best thing I have done so far. A 10x10x10mm cube now measures 9.98x9.97x10.02mm.

So for everyone out there who also gets wrong dimensions for your x and y axis: Watch your pulleys when you print something or when you just move the printhead. If they wobble then this is most likely your problem.

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