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A Little Cooling Story  

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burtronix
(@burtronix)
Estimable Member
A Little Cooling Story

This is more of an instructional than a plea for help. I figured it out enough to make this part & maybe some others can benefit. But I also expect there may be more that could be done or more to be learned from the experts here.

The part on the left was printed facing right, so that the right side was exposed to the cooling fan blowing from the rear of the Mini extruder. As you can see, the overhang-angle on the left side was not forming nicely, but the same mirrored feature on the opposite side was just fine. So I decided to turn the part 90 degrees so that this whole thing faced to the rear & directly at the cooling fan. The part on the right is the result (with a few additional tweaks I made to reduce the severity of the overhang). So success! Right? Maybe not completely.

The backside corners (not shown) were not as thin or over-hung as much, but the layers sagged just a bit compared to how they looked when they were facing the cooling fan. I think they were passable, but I still wanted to improve them. I looked at Prusa Slicer settings to see if there was anything else I could do to increase cooling. Cooling was already set to 100%, but I noticed that because this was a small part, the print speed actually slowed down to allow more cooling between layers.

Up to this point, I had been printing singles & tweaking the design, but now I was ready to print multiples & tweak the process. So I sliced a batch of 4, faced the vulnerable thin overhangs to the rear, & printed away. Not only did the overhangs come out better, but the time per-part was reduced almost 10%! That's the part on the right side.

But here's my question: is there anything I can do to increase cooling on the side facing away from the fan or overall, without resorting to turning the part or sticking extra instances of it on the print bed? This worked for me this time, but I could envision a situation where those aren't desirable options.

Here are the specifics:

  • Original Prusa Mini, stock, 0.4 mm nozzle
  • Firmware v 4.3.4
  • Prusa Slicer 2.4.0
  • Auto-cooling enabled, with min & max set to 100%
  • Printing Prusament PLA Mystic Brown
  • Using standard Prusament profile
  • Layer height: 0.15 Quality
  • Gyroid infill 15%
  • The model pictured is my own design. It's about 30 mm wide for scale.

Whatever you find to do with your hands, do with all your might!

Posted : 15/02/2022 10:10 pm
fuchsr
(@fuchsr)
Famed Member
RE: A Little Cooling Story

Thanks for sharing, and yes, in general it's a good idea to print multiple copies of small objects. 

I don't know what else you can do. For the Mk3S, there are alternative shroud designs that claim to improve airflow around the nozzle. I've tried quite a few and am back to the stock shroud. I guess under certain circumstances those "improved" designs may in fact yield superior results, I just didn't see any of that in a few weeks of testing each, and a couple performed significantly worse.

For the Mini, I haven't really seen many. One example is https://www.prusaprinters.org/prints/52553, but just from the looks of it I wouldn't be holding my breath to expect any improvements. My Minis have Dragon hotends, so I never considered any alternative shrouds because I'd have to adjust the mounts to make them work, I assume. 

Posted : 16/02/2022 4:25 pm
burtronix liked
bobstro
(@bobstro)
Illustrious Member
RE: A Little Cooling Story
Posted by: @burtronix

[...] I looked at Prusa Slicer settings to see if there was anything else I could do to increase cooling. Cooling was already set to 100%, but I noticed that because this was a small part, the print speed actually slowed down to allow more cooling between layers.

I think that "slow below" option is another setting (along with the support top layer parameters) that PrusaSlicer inherited from the original Slic3r that hasn't kept up with the times. In digging around on this same issue -- I've got a really low end printer with NO part cooling -- the thinking at the time was that keeping the fan over the just-printed part would improve cooling... for the then most-common ABS filament types. With PLA and newer materials, my experience has been the same as yours. For printing narrow parts on my crummy printer, I print a 10x10mm "cooling tower" the same height as my print and print with the part and tower at opposite corners. There's enough sparse infill in the tower to let the print cool for a few seconds. I generally disable the "slow below" feature unless there's a specific reason to enable it.

My notes and disclaimers on 3D printing

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

Posted : 16/02/2022 4:58 pm
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