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Oj00

UM3+UM3E Holes printing under-size

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I have done a lot of research into this and it seems to be caused by many factors and there isn't really an answer how to fix this.

What I have done to minimize this is print a test piece of varying diameters (10mm-100mm for me). Then i measure the actual and compare it to the virtual size. This gives me a good idea of what size a hole will come out as and I adjust the model before printing.

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All technologies including FDM and injection molding have weirdnesses like this (e.g. in injection molding if you want 90 degrees corners your cad part better not have 90 degree corners).

I add typically .4mm DIAMETER (not radius) to all vertical holes.

The cause of all this is that the filament sticks to itself while cooling and shrinking in a fraction of a second as it comes out of the nozzle and it's like sticky mucus (like snot). It's pulling like a liquid rubber band and pulling inward on these vertical holes.

Horizontal holes don't need to be adjusted in diameter (but you might want to put pointy tops to the holes).

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