UM3+UM3E Holes printing under-size

[Oj00 5]

Hi,

We've recently been having a lot of issues with holes (both round and hexagon) printing under-size. I know this can be common with FDM printers but is there not some way Cura can compensate for it?

Thanks,

[rebekah_harper 60]

If you apply the horizontal expansion but enter a negative value it will compensate but it will apply it to the whole model. Having said that if the holes aren’t the right size then nor would the model be the right size.

[pa9k 4]

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.

[gr5 2,271]

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).