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Prints always 0.4 mm to small

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Posted · Prints always 0.4 mm to small

Hi! I was just wondering why almost everything I print are approximately 0.4 mm to small in x and y direction (not in z direction)? This applies both for holes/circles and squared objects.

Example: I want to print a rectangular object 40x60 mm, with a hole in the middle, 20 mm diameter.

The results will be approximately 39,6x59,6 mm, with a diameter of 19,6 mm.

Also, the nozzle size is 0,4 mm, which is the size that are missing in all directions (except z direction). It feels like the printer is skipping one line/path.

Or could this be because of shrinkage? Is it possible that PLA plastic is always shrinking approximately 0.4 mm, no matter how large the object/feature is?

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Posted · Prints always 0.4 mm to small

Inner vertical holes will indeed be about .5mm smaller. Also outer corners. This is because the hot PLA cools a bit in a fraction of a second and so shrinks slightly and as it is being placed acts like "snot" (stuff from your nose). Like a liquid rubber band. Because it is so stretchy it is pulling inward - but still in liquid phase - and so outer corners and inner holes are all too small. Especially on sharp curvatures like small holes or sharp corners (like those on the tip of a star).

However the sides of your rectangular object are not affected by this. I'm not sure why that would be smaller. .4mm versus 60mm is 0.6% which seems a bit high. Typically PLA shrinks more like .3% from the glass temp down to room temp. So I'm not certain what is causing that but I'm not particularly surprised.

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