3D Printing Face shields -> Print quickly and reliably

Hi guys !
First, I hope you are fine and your family too.

I did not post anything since a long time.
I dropped a few 3d printed parts to volunteers assembling face shields for people fighting the coronavirus.
I am pretty amazed how fast the 3d printing community reacted and how big it is becoming.

How to print "quickly and reliably" ?

I put quickly in bracket, because of the speed and the throughput.
Yes for the throughput, speed matters but at what risk: reliability of the print and reliability of the machine.

Safe Slicer settings:

• Larger Extrusion Width (Nozzle: 0.4mm -> 0.5mm, 0.6mm -> 0.72mm, 0.8mm -> 1mm): the geometry of the tip of your nozzle and the geometry of the part to print is the limiting factor.
• Larger Layer Height but not overdo it ( Nozzle: 0.4mm -> 0.28 to 0.32mm, 0.6mm -> 0.4mm): some tuning is needed, the part can become too weak (see cooling/temperature parameters)
• Tune number of perimeters/insets: given the geometry and the extrusion width you can manage to reduce the number of passes made and reduce/avoid the slow shaking movement of the top/bottom or the gap filling (overlap setting is your friend)
• Use Concentric infill for Top/Bottom layers: linear infill or zigzag infill will just take more time
• Cooling parameters: No fan on PETG print for instance, try to reduce it, it makes stronger parts and you can print faster. Set the print time per layer down to 5 or less seconds.
• Keep the same print speed all around, if there is a bit of ringing it does not really matter.
• Keep a safe margin on the extrusion throughput, go to max 75% to 80% of the theoretical limit (https://www.printitindustries.com/pages/print-speed-calculator)
• Print with higher temperature but don't overdo it (retraction can become ineffective after a threshold)

Example printing a single part on PETG at 230C on an Ender 3:
Standard Print Speed 40mm/sec, Retraction speed 25mm/s with 6mm
Layer Height 0.2mm with 0.4mm extrusion width, base line 2h22m

• Same speed with larger extrusion width + cooling settings + concentric top/bottom infill:
  0.4mm to 0.5mm with 0.2mm layer height: 1h52m
• Same speed with larger layer height (0.5mm extrusion width instead of 0.4mm):
  • 0.24mm layer height 1h33m
  • 0.28mm 1h22m part good
  • 0.32mm 1h12m part correct
• Increasing speed from 40mm/sec to 50mm/sec
  • 0.32mm 1h05m (part too weak, start to have under extrusion after short retractions sequences)
  • 0.28mm 1h12m part correct

What about reliability ? 2 minor failures only caused by me ^^
Same quality of the prints over and over, print start and you go.

Happy 3D Printing !