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Dimensional accuracy model/print?

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I am new to 3D printing, so maybe that's not an issue and normal, but I think I have to ask the experts.


I designed a simple rectangle 17x65mm and printed it with the "Fast" profile on my UM3 with UM PLA. In Cura the dimensions are still correct. But printed the rectangle actually has 66mm and 17.5mm. Scaling in Cura was 100%


I think it could be something with the "elephant foot" thing, the rectangle is only 1mm thick, but not sure if the dimensions are generally quite accurate or not when printing in 3D? So is it normal that the actual print differs a little bit or more from the source file?



BR Christian 

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Where do you measure your model? It can be that the edge of a corner or the bottom might be slightly fatter than the 'rest of the walls/model'. So if the corners seem to bulge instead of being a sharp corner, this may seem like the entire dimension accuracy is relatively low, while in fact we could try to get that corner in better shape. For example, by slowing down the print. 

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You are right, but I tried to measure to avoid those bulges. My failure was, that I printed nearly every test object with the "Fast" profile and there the accuracy is not as good as in "Normal" or "Fine".


With the normal profile (0.15) the accuracy is quite good and I just have +/- 0.2 max. difference to the actual dimensions which is good for the 3D printing technology I think. Just in inner holes there is more difference, but I read that this is also "normal" and I have found some options to play with to optimize also the inner holes.

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Here are some design tips, that help you to achieve good precision with 3D printing.

Of course the values depend on your printer / material etc... that's something you can only find out by trying and playing.


- due to the nature of the data format STL, diameters and radii (no matter if inside or outside) get smaller during the data conversion. So you should design them a little bigger than desired, a couple of tenth millimeters, depending on the conversion resolution


- the bigger outside corners @SandervG mentioned get smoother, if you design them with a small radius (~1 mm)


- if you part has only one measurement that should be as exact as possible, try to orient that in Z. Thats for my experience the most accurate axis, though it can only print multiples of the layer height + the initial layer height


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