Automatic Printing of 3dVerkstan face shield visors with a Prusa Mk3/Mk3s

The Hook-lift-push method for automatic printing

  • In this mode, the printer prints 1 part, inserts a hook into a hole in the part, peels if off, pushes it off the build plate and starts printing the next one
  • Demo: https://youtu.be/Xhyw_2FNBYU
  • Currently installed on 6 Prusa Mk3/Mk3S printers and working almost non-stop throughout the day and night
  • We discovered that just pushing the print off the bed is ineffective on the prusa, as the PEI print bed is pretty strong and its X/Y axes are too weak.
  • Adding a hole to the STL file and using a hook to first peel the print off the bed proved much more reliable

If you have trouble with any part of the guide, contact me on basecamp, or through email: mironandrzej1@gmail.com

Parts for this modification:

  • wire hook, for lifting the print off
  • printed pusher, for pushing the print clear off the bed
  • custom GCode, for moving the hook and pusher

Tools/Materials:

  • 1.6mm mild steel welding rod. (Any wire roughly that diameter, that is stiff enough to repeatedly peel off a part should also work)
  • 4 M3 washers
  • 2 M3x20/M3x25 screws (if not available, the original screws holding the hotend fan in place can be used)
  • Pliers
  • 1.75mm PETG filament
  • 1mm nozzle for prusa
  • 7mm socket wrench (or pliers) for changing nozzle

Instructions

The shields will be printed with a 1mm nozzle for speed, but before installing it, print off the pusher for your model and the wire bending jig with a 0.4mm nozzle using PETG.

The pusher/fan shroud sits close to the nozzle, and should be printed in PETG instead of PLA.

I have provided files for the Mk3 and Mk3S, as that's what I've got access to.

If you have a different printer and are wanting to adapt this process, you will need to download the stl file for the part cooling fan shroud, and modify it to have a flat piece at the front as I did. Supergluing something flat on your print head would also work.

The wire bending jig is not strictly necessary, the wire could be bent with only pliers (The hook on the end is 5mm and the whole wire is 55mm long)

If you are making more than one, printing a jig will help you make them consistently.

The jig needs an M3 screw threaded into the single hole.

Making the hook

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  1. Hold 5mm of the wire with pliers Make a 90 degree bend in the wire to make the hook

  1. Put the end of the hook in the marked hole of the jig

jig

  1. Bend the wire around the M3 screw
  2. Take out the piece of wire from the jig

hook

  1. With pliers, make sure the 2 pieces of wire are parallel to each other

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  1. Snip off the rest of the wire, so one end isn't longer than the one with the hook

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  1. Bend the hook outwards slightly, about 20 degrees, so it doesn't bump into the left threaded rod when installed.

  2. Wire hook finished

Installing the pusher

1.Unscrew the front print cooling fan and printed fan shroud that the fan connects to

2.Extract the nut (if there is one, like in MK3S) and insert it into your new part

3.Put in your new part and assemble everything back

Prusa has assembly instructions online if you need help https://manual.prusa3d.com/c/English_manuals

Installing the hook

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Before doing this, install the 1mm nozzle, run a print, and fiddle with the "Adjust Live Z" to get a good first layer. The print should stick reliably, but not be too hard to peel up, as that will stall the motors. The reason for doing this is the hook needs to sit at an exact height from the tip of the nozzle.

  1. Unscrew the 2 left screws from the side fan
  2. If you have longer (M3x20/M3x25) screws, use these in this step, otherwise use the screws you took out.
  3. Put 2 washers over each screw.
  4. Screw in both screws with them sticking out slightly, such that the hook can be slid in between both pairs of washers.
  5. On your prusa, go to "Calibration" -> "Mesh bed leveling" (this makes the nozzle sit almost on the print bed, the correct height for the next steps)
  6. Go to "Settings" => "Disable steppers" and move the head over the centre of the print bed by hand.
  7. Install the hook: put it between both pairs of washers. Make sure it can still slide up and down
  8. Put a full size SD card (it's ~2mm thick, half the height of the faceshield print) between the hook and print bed.
  9. Gently push the hook down so it touches the SD card
  10. Make sure the print head still homes as normal. If the top part bumps into the left z-screw nut, the hook is too long, use a different hole in the jig or fix with pliers. If the hook bumps into the z-screw, bend it out the way more.
  11. Tighten the screws. DO NOT tighten these too hard, as they are threaded into plastic, but enough that the hook stays in place and will not move after being used to pull up successive prints. If the hook is not secure enough, try using a dab of superglue.

GCode

To make the hook and pusher work, I wrote some custom GCode, which is included in the Prusa Slicer project attached here.

It also has the exact position of the print on the bed and settings for 1mm nozzle.

They are not perfect, so any changes to them are welcome.

If you want to make changes, it can be edited by opening the project, enabling 'Expert' mode and going to "Printer Settings" -> "Custom GCode" -> "End G-Code"

The repeating of the program is done by opening the .gcode file in a text editor and copying and pasting the lines after line 43 (when the printer finishes set up) 50 times (copy and paste it 10 times, then 5 times with that chunk of 10)

Prusa slicer settings

  • Bed set to 60 degrees for easy peeling off of the print, if the adhesion is too strong, this can be lowered by a couple degrees in addition to adjusting the z-layer height
  • Fan turned off, which stops the nozzle cooling down as much, which means more volumetric flow
  • Layer height set to 0.625mm, so that each 5mm high print prints in 8 layers