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Dimensions of the Parts are not exact

Wed Jul 16, 2014 12:22 am

I use the software to slice and print objects wich are suppose to fit together. I can do that with for example slic3r but with simplify3d the holes are to small and the outlines are to big. I'm talking about 0.5mm in a 19mm hole (it's 18.5 actally). That is not a big difference but it causes that the parts not fit together.
I could rework the CAD but in my opinion the error has to be eliminatet on the origin.
Perhaps someone has a similar problem, eventually it is possible to tweak the extrusion with. I have this parameter on auto and it calculates 0.6 for a 0.5 nozzle.


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Re: Dimensions of the Parts are not exact

Mon Aug 04, 2014 10:58 pm

It's very frustrating. My experience with this issue brought me to this forum looking for answers.

I just printed a rectangular test part, going back to S3D's default settings for Makergear M2 / ABS after much tinkering, and found the outer dimensions are relatively spot-on (hundredths of a mm bigger) while the inside dimensions are too small (up to .6mm too small). This is the same results as during messing with the settings. PLA had better dimensional accuracy than ABS but I'm not sure how that can be. I am trying to print mating parts but they can't fit correctly if the printer makes features too small. I switched from slic3r to S3D because of fitment issues with PLA but did not expect having to mess around this much with Creator.

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Re: Dimensions of the Parts are not exact

Tue Aug 05, 2014 9:26 am

just as little note here, pla will usually always have better dimensional accuracy because it has less thermal contraction. not saying the whole issue is that but all plastic shrinks as it cools. abs and nylon are 1-2% for instance. this needs to be taken into account. the problem with 3d printing and not having a heated chamber is this shrinking is uneven because its cooled layer by layer. this can make your parts shrink in unexpected ways or directions. the direction and way it shrinks can also have alot to do with the shape of the part. extrusion settings and infill also plays a big roll. settings in slic3r dont transfer directly to s3d so if the part is extruded differently from one to the other you can have the part shrink differently as it cools. again im not saying this is 100% the problem but it may be half of it. even in injection molding you need to take into account the shrinkage of the different plastics your using.

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Re: Dimensions of the Parts are not exact

Tue Aug 05, 2014 12:52 pm

I have had this, also from thingiverse, prints that are meant to fit other things like iPhone cases always printed to small. This is because of material shrinkage, made worse by printing to fast. My solution for 'critical' fitting parts was to simply halve the print speed, this allows the plastic to cool before the next layer. After I did this I found the majority of prints were dimensionally accurate.

It seems that there can be a build up of heat, layer by layer that shrinks more when cooled. For pla an extruded fan os always a winner.

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