PrusaSlicer Bug? Non-circular Holes  

RE: PrusaSlicer Bug? Non-circular Holes

can you print the model at 45degrees? so that the top of the hole isn't unsupported?
can you use supports?
can you use hexagonal holes? then a flat top will look normal!

Prusa address this by mixing circle and polygon as above

this is one of the holes in the X carriage end pieces, intended for 8mm smooth rods to seat in

RE: PrusaSlicer Bug? Non-circular Holes

Wow that’s interesting! I have never noticed that the OE parts are modified like that. I can’t modify the original files because I print for customers, and a modification of their original file could get me into trouble. 45 degrees could work in some cases, but at the cost of time and support material. I was hoping there is a slicer setting I could tweak

RE: PrusaSlicer Bug? Non-circular Holes

as Scottie used to say “http://www.bored.com/findquotes/cate_828_Physics.htm l">Ye cannae change the laws of physics”

your parts are sliced into layers, the thicker the layers the bigger the steps at the top and bottom of holes... however nozzle diameter plays a big part at the top of the hole

Both images have variable layer height with 0.07mm around the top hole, 0.15mm around the middle hole and 0.3mm layer height around the bottom hole you will notice the sides of the hole are more regular with the smaller layer heights, BUT the flat at the top of the hole, is wider with smaller layer heights...

Note that the left hand image has smaller flat tops, than the right hand image...   this is because I have changed the nozzle size, the left model demonstrates a 0.3mm nozzle, the right hand model demonstrates a 0.6mm nozzle

when there is nothing for the bridging perimeters to squish against, they tend to remain circular and nozzle diameter... 

what nozzle size and layer height are you using?

the gravity is strong around here, and unsupported shallow overhangs, are likely to droop

shame you can't orientate at 45degrees, the flats dissapear  

🙁

regards Joan

RE: PrusaSlicer Bug? Non-circular Holes

And what the OP is also missing is the fact the bottom of that hole is also flat, not round. 

ps: and yes, the slicer could do better when handling the top surfaces of holes.

RE: PrusaSlicer Bug? Non-circular Holes

Thanks Joan for that excellent and detailed explanation! I am using a .6mm nozzle at a .1mm layer height, so I would expect the bridging perimeters to have plenty of material to smoosh into. I am a little confused by the blue area at the top of the hole - is that the actual tool path, or just an area that prusaslicer is warning me is a gnarly overhang? Because in a couple of those pictures it looks like the toolpath is diving into the blue abyss of bridging overhang settings, but it’s hard to tell what the fat blue lines are actually indicating.

RE: PrusaSlicer Bug? Non-circular Holes

I can see that the bottom of the hole isn’t round either, but at the bottom of the hole, material is subtracted from the actual model, which is OK, but at the top, the slicer is adding material where there shouldn’t be any. Right? The several other slicers I use handle holes differently.

RE: PrusaSlicer Bug? Non-circular Holes

It looks like in your slice there is a detail that is confusing Plicer.  There shouldn't be any multi-height extrusions because the Mk3 can't normally do that.  I suspect you've set something in the extrusion widths that is messing with Plicers algorithms. 

RE: PrusaSlicer Bug? Non-circular Holes

Posted by: cody.l2

I can see that the bottom of the hole isn’t round either, but at the bottom of the hole, material is subtracted from the actual model, which is OK, but at the top, the slicer is adding material where there shouldn’t be any. Right? The several other slicers I use handle holes differently.

This is not correct, nothing is subtracted or added. At the bottom of the hole the filament is totally supported by the filament beneath whilst at the top of the hole there is nothing below to offer support so the filament droops slightly under gravity. The same amount of material is extruded in both layers but the end result is different.

You could look at variable layer height (the icon with increasing line thicknesses top right in PrusaSlicer) to use the effect Joan shows to your advantage.

RE: PrusaSlicer Bug? Non-circular Holes

Aye. Gravity bumps can affect 3D prints captain, it will take me 48 hours to sort it. Scotty!!! Ok Captain I can solve it in the next hour.  The Earth is lumpy. We come in peace.