MK4S Bridge printing  

MK4S Bridge printing

Hi Everyone.

It seems I'm on a journey and… it's gonna be a long one to unpack.

I have a Prusa MK4s which seems to do awful bridges. I went to the Prusa blog / articles on bridging, where it basically says (I'm paraphrasing here) to drop the speed and drop Bridge flow incrementally in PrusaSlicer until we get the result we are most happy with. ( https://help.prusa3d.com/article/poor-bridging_1802)

So… there I was starting off a journey, that I'm still not at the end of, but ran out of ideas…

I download this model ( https://www.printables.com/model/109216-bridge-test-fast-low-cost-ender-3) off Printables and start "tweaking" settings. Also, below there's some general Printer stuff:

• Filament: PLA (Rosa3D Basic White and some gray leftovers)
• Nozzle: 0.4mm High Flow ObXidian ( https://www.prusa3d.com/product/e3d-prusa-nozzle-high-flow-obxidian-0-4-mm/)
• Steel Sheet: PEI Original Prusa
• Printer Mods: none.

Bridge test model (skinny)

1. A = 0.1 layer height
2. B = 0.2 layer height
3. C = B + Thick Bridges
4. D = C + Lowered Bridge Speed (10mm/s) + Brim
5. E = D + 0.95 Bridge Flow
6. F = D + 0.85 Bridge Flow

At this point I see on YouTube this video with settings in OrcaSlicer: You asked for PERFECT bridges in OrcaSlicer, so we built THIS

So, I downloaded OrcaSlicer Nightly/Dev And started printing the model from Printables ( https://www.printables.com/model/1482067-bridge-density-experiments):

Settings:

• Bridge Flow - BF: 1.0
• Bridge Density - BD: 105% > 114%
• Default Bridge Speed - BS: 50mm/s
  • 
• BF: 1.1
• BD: 106% > 110%
• BS: 50mm/s
  • 
• BF: 1.2
• BD: 103% > 107%
• BS: 50mm/s
  • 
• BF: 1.3
• BD: 100% > 104%
• BS: 50mm/s
  • 
• BF: 1.4
• BD: 97% > 101%
• BS: 50mm/s
  • 
• BF: 1.5
• BD: 94% > 98%
• BS: 50mm/s
  • 

After thinking that I forgot to reduce the speed, I reprinted them (and more) at 10mm/s

• BF: 1.0 • BD: 105% > 120% • BS: 10mm/s
  • 
• BF: 1.1 • BD: 106% > 120% • BS: 10mm/s
  • 
• BF: 1.2 • BD: 103% > 120% • BS: 10mm/s
  •     
• BF: 1.3 • BD: 100% > 120% • BS: 10mm/s
  • 
• BF: 1.4 • BD: 97% > 115% • BS: 10mm/s
  • 
• BF: 1.5 • BD: 94% > 113% • BS: 10mm/s
  • 
• BF: 1.6 • BD: 94% > 109% • BS: 10mm/s
  • 
• BF: 1.7 • BD: 94% > 109% • BS: 10mm/s
  • 
• BF: 1.8 • BD: 94% > 100% • BS: 10mm/s
  • 
• I could post the backs of the prints, just to see why some were not considered good, but this post is already too large.

Results were so good that I found a few to be quite good (Perfect!!!!), such as: BF1.1/BD119; BF1.2/BD115; BF1.3/BD112;BF1.4/BD109 or BD112; BF1.5/BD105; BF1.6/BD105; BF1.7/BD101 or BD102; BF1.8/BD97

I was hoping to get a combination of some BridgeFlow value and BridgeDensity 100%, but BF1.8 went below 100% so I thought I missed the mark.

• WHY Bridge Density 100%? Because it's the default value in PrusaSlicer and it's not available for tweaking.

However, I switched back to PrusaSlicer and printed two bridge test pieces with BF1.7 and 1.8 at 10mm/s speed. The result was good.

I switched back to the initial test model, albeit just the long bridges part and tried a print. Spaghetti galore as the bridges starting to droop.Tried a second print but cancelled it when spaghetti was "back on the menu". I can't understand why does it droop in the "skinny" bridges, but not on the BF/BD model…

It got me thinking that the test pieces for BF and BD had sidewalls. So I got the model without sidewalls and printed again from PrusaSlicer with BF ranging from 1 to 1.8:

Results were not terrible.

As a last ditch effort, I put the BF/BD model, the "skinny" bridge model and a widened version (to see if there were any changes) on the same plate, added a brim and printed with BF1.8 and Bridge Speed of 10mm/s: BF/BD model was ok. The others had strings, but no spaghetti…. WHY????? As there were the same damned settings???

Please help, I'm losing my mind here… (and Yes, the filament was dried). I do realize that the test prints and the video instructions go against the instructions from the Prusa blog page, but seeing in practice the opposite effect (bridge strings sticking together) makes me ask for HEEEEEELP!!! 🙂

In case the goal is still unclear, I need to print a bridge without supports and be good enough to not have strings underneath it.

Thank you in advance to whoever accepts the challenge to read the above and reply back 🙂