R4G Extruder for Prusa, a DIY Bondtech Upgrade / Geared Extruder

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This is the R4G extruder for Prusa printers, where G stands for Greg or Geared. It's a DIY "Bondtech upgrade" that requires a very limited set of additional parts. It is derived from the Prusa R4 extruder of the MK3S (https://github.com/prusa3d/Original-Prusa-i3/tree/MK3S) and uses its opto-mechanical filament sensor. However, you can also use it without any filament sensor. The design is somewhat beta, so venture here only if you are adventurous. In addition to what you get with a MK3S, you will need: * 1x Bondtech shaft assembly * 1x Bondtech motor drive gear * 2x 5x8x2.5 mm bearings * 2x DIN 562 M3 square nuts (+ some extras to cover those you won't be able to extract from the original printed parts) * 1x M3x18 screw * 1x PTFE tube You can get the Bondtech parts from a BMG extruder or purchase them individually as spare parts. If you want to just test the setup, you don't need to invest in a pancake stepper motor. For long-term use, it's a clear advantage to have one. The motor shaft length must be maximum 20 mm. If you want to use a motor with a shaft length that is more than 20 mm, increase the height of the spacer when you print it (22 mm shaft -> 2.6 mm spacer). You may need to increase the length of the 3 screws that hold the motor too. Avoid purchasing a 0.9° stepper; they offer no advantage in this setup and will likely degrade the quality of your prints. It's recommended to use a 1.8° or 0.9° stepper with microstepping enabled. From here, you should be able to make your way with the R4 instruction assembly (https://manual.prusa3d.com/Guide/5.+E-axis+assembly/1055?lang=en). You will also need to change the PTFE tube so it is flush with the gears when you install it (approx. length 62.5 mm). It's highly recommended to use a collet clip on the coupling, alternatively, you can put some adhesive tape on the PFTE tube where it exits the hotend radiator so it will be clamped when you assemble the 2 parts of the body. Without that, your PTFE tube will move and will get quickly damaged by retractions/de-retractions. Since you now have a geared extruder, you need to change some settings on the printer: Changing eSteps/mm is a must; changing maximum feed rate is highly recommended (because you have a 3:1 geared extruder, motor will rotate 3x faster to achieve the same feedrate). Changing max feedrate for extruder: - M203 E40 (set the max feed rate to 40mm/s, 1/3rd of the stock value, higher value may work too but you need to experiment) - M92 E830 - M500 (to save the settings in the EEPROM) On the MK2: - M92 E415 - M500 If you like to print fast on a MK3(S), the default 830 steps/mm may be a limit. You can go the following route to avoid that: - Set your defaults as indicated above - In your slicer startup gcode add: M350 E16 M92 E415 M203 E80 This will set extruder motor to 16 microsteps (vs. default 32) and adjust eSteps/mm and maximum feedrate accordingly. Microstepping is not saved in the EEPROM, that's why this needs to be in your startup gcode. CREDITS: - Prusa R4 extruder: https://github.com/prusa3d/Original-Prusa-i3/tree/MK3S - CAD model for Bondtech gears: https://github.com/BondtechAB/Bondtech_Prusa_i3 R4G extruder is licensed under GNU GPL v3.0