My brother and his wife (being the awesome people they are) decided to get me a Raspberry Pi 4 - 2GB for my birthday as well as giving me his old monoselect duplicator i3 plus. My brother 3D prints as a hobbyist and makes useful prints as well as nick-knacks, but doesn’t go into the weeds on printer issues like I have on occasion. This duplicator plus was an open box unit for he ended up getting it for great price. He had been struggling with this particular printer for a while trying to get the filament to feed properly and consistently, but ended up inevitably shelving it in favor of an Ender 3 he purchased. The TLDR on this one is not surprising; the printer needed a bit of work, and wont be able to have a few features of a more modern printer.

My initial impression of this printer was..   damn its heavy, or at least its much heavier than my Prusa Mk 2.5s. This thing could make a perfect boat anchor with very little modification. The frame seems sturdy, even if the lack of 3D printed parts makes me a little sad. My brother installed a Y-axis tensioner, but the X-axis was super loose and has no stock way of being tensioned as far as I can tell without sacrificing two zip-ties. The Bed did not move consistently, and was caused by a locking nut being positioned too close the belt wheel.

There was no auto bed leveling, so this had been my first experience with manual leveling. This printer had an absolutely terrible Z end-stop mounting system, which makes the manual leveling much more of a pain than it needs to be in my opinion. With that said I installed a BL-Touch Sensor because it was borderline necessary upgrade for this printer.

I was in the process of re-using the original main-board, but ended up killing the extruder stepper motor driver. Instead of scrapping the project, I ended up spending a ton of time designing new mounts for an Bigtreetech SKR mini V1.1 and a TFT24 and using newer TMC2208 stepper motor drivers. Although it was a ton of work and the drivers needed active cooling, this seems to have been worth it. There are a few bugs related to Marlin 2.0 and this Bigtreetech display isnt perfect, but these are still well ahead of the 120$ oem mainboard replacement considering they can be replaced  for half as much without re-buying the stepper motor drivers.

I did end up frying a SKR mini after accidentially shorting the extruder fan wires by accident.  15 dollars on Amazon and two days later later I was back in business. The SKR Mini is somewhat limited in the ports it has, and does not have a heated bed mosfet. I also had to remove a capacitor and resistor from the mainboard on the Z+ endstop pin so it could be used by the BLTouch for its data communication. I will have to do the same later if I am going to use a mosfet to control extuder fan on/off so it isnt continuously running when the printer is just sitting there.

This has been my first experience with modifying Marlin, and damn its a bit more of a rabbit hole that I thought it would be. I also had some issues with tiny vibrations that effected surface quality of prints. I think I ended up resolving this after replacing the carrage parts with new prints at a hundred percent infill. I installed a rear mounted Z brace as well, but did not solve the issue. It will be good for printing tall objects at faster speeds. There are a few quality of life things that still need to be done, including getting a instance of octorpint running on a pi and getting the Z axis changed over to a TMC2208 as well, but the printer is usable as it is now.

I have to say that while a large distraction from the CNC project, it has been educational... although I probably should be spending that time unpacking and working on fire station paperwork. All-in-all, I think it will be good having a reliable second printer to expidite printing activities for everything including the CNC design.