[PROBLEM] Bridge infill in mid-air when increasing number of perimeters.
Hello all,
I've been having a hard time getting the bridges to print properly for a while on my modded Ender-3. They're getting printed in mid-air.
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SITUATION: I performed a clean install of PS 2.2.0 rc4 and used the pre-configured profiles that come for my printer.
The only settings I changed on the printing profile are:
Detect thin walls (enabled)
Detect bridging perimeters (enabled)
Perimeters: 4 (changed from the default 2)
The part has 1.6mm thick walls
Here's the STL file of my test part: https://drive.google.com/file/d/1ZwnU2j9Q8ikSUSBB6sowNaQKdII9CRX_/view
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SCREENSHOTS OF THE PROBLEM:
First image shows the slicing result when trying to print with 4 perimeters instead of 2 (second image).
Experimenting a little bit, I see that the larger the set perimeter value, the least perimeters that the bridging will rest on. (E.g. if 2 perimeters: the bridging strands rest on 2 perimeters, if 3 perimeters: it rests on only 1. In case 4 perimeters: the bridging strands don't have any perimeters left so it gets printed mid-air)
Is this normal?
You may say..."Okay, just set it to 2 perimeters" but what if I have another part that required thicker walls (E.g. 8 perimeters) and there happened to be a bridging somewhere else between walls that are as thick as only 4 perimeters ?
Thanks
RE: [PROBLEM] Bridge infill in mid-air when increasing number of perimeters.
I wasn't clear on first reading your post what the issue was, but if you view the model from underneath in preview mode it's clear. Sliced with 2 perimeters, bridging strands start and stop atop the perimeter walls:
If sliced with 4 perimeters, they start and stop with a suspended layer which itself shows as a bridge:
I don't have a good answer for your on this, but it is probably worth opening an issue on the PrusaSlicer github page to ask the question.
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He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: [PROBLEM] Bridge infill in mid-air when increasing number of perimeters.
Set your infill to 5% concentric, slice and see that the bridge is now fully supported.
Even works for 1 perimeter, but of course you have more walls due to the concentric infill.
I also use this trick to support bridges with modifiers.
Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet.
RE: [PROBLEM] Bridge infill in mid-air when increasing number of perimeters.
FWIW: The bridges do work with 4 perimeters. Not sure why they print differently though.
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: [PROBLEM] Bridge infill in mid-air when increasing number of perimeters.
Didn't read the OP post too clearly and now understand, he is trying to print with 4 perimeters and this is when the bridging prints in mid air, which I can confirm when viewing the slicer preview. Still, using concentric infill with 3 perimeters, actually results in 4 perimeters and a fully supported bridged layer.
Very strange behaviour from slicer, but this would result in a solution that works for the OP.
Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet.
RE: [PROBLEM] Bridge infill in mid-air when increasing number of perimeters.
I've run into this 'issue' a few times, and I can see why it exists: If you define the minimum vertical shell perimeter as 2, then the slicer will put no less than 2 shells in. If the part in total is only 2 perimeters thick, that means there will be no room for the bridge to connect because that space is already occupied by the perimeter. If the slicer were to remove at least one shell to make room, you'd violate the "2 shell minimum" definition that you've set. In this specific case, the workaround is to set the minimum vertical shell perimeters to 1, as that would allow room to fit in the bridge.
Another workaround would be to use a finer nozzle so that more shells will fit in the same physical space.
Truth be told, I really wish PrusaSlicer would throw a Warning whenever a bridge segment cannot be properly supported by infill/shell. This has caused me many headaches when the slicer codes bridges that end in space as this clearly does not print properly.