Vertical holes oval

Mostly Printed CNC - MPCNC Advice
#1

Hi1

I’ve just started printing parts for the MPCNC. Finally!
I’m printing “RollerMounts” at the moment.

When printing part has two 3mm vertical holes (I think 3mm)
From some reason, those holes end up oval!

So, I’ve printed 30x30x30mm test cube with two vertical holes in it, 6mm and 4mm

Pics attached

On first picture you can see how is cube oriented when printed.
On other pictures you can actually see how oval holes are

All other parameters of the test cube are fine

I would really appreciate if anyone could help me solve this.

I presume that small size errors of 0.2mm width/length/height won’t affect anything in the assembly proces but I would like to eliminate oval holes to eliminate any room for screws to play.
Or is apsolute print accuracy in every aspect essential?

Thank you!
Regards,
Walter

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#2

Holes in that orientation are always going to be less round. Usually it is just a little sag or cooling thing. No issues.

#3

Thank you for the info!

Will proceed with printing…

#4

In prints like this I just drill/clean up the holes with a 3mm sharp drill, best way is to print the parts with the holes pointing up.

In most slicers there are a feature called ‘horizontal expansion’ or similar because holes always tend to come out a tiny bit smaller. This have been super useful for mechanical parts(i print prototypes and builds robots for a living), so instead of modeling a 3mm hole to 3.1 to account for shrinking, you set ‘horizontal expansion’ to account for the shrinkage.

#5

I’m not sure what you are using as a layer height, but there is a marked difference in holes and overhangs (which is what is happening at the top of the hole) if you use smaller layer height. If you haven’t tried it, try .3 , .2 , .1 and you’ll see.

#6

All prints are done at .2mm layer height
I haven’t tried going for .21, .22, and so on

I have calibrated extruder to truly extrudes 100mm of filament when I tell it to and calibrated Z axis steps so printed cube height would match dimensions of the test cubes .STL

I’ll try .21, .22… layer heights and see what I get out of it.

On parts list it is suggested that prints should have 3 perimeters/shells
What about top and bottom layers?
Also 3 or maybe more?
Would 4 add any strength or would it be just a waste of time and plastic?

Thanks!
Regards,
Walter