Adopted 2nd Prusa MK3 continuing issues... next steps?
I have a Prusa MK3S that I upgraded from an MK3 over the summer. I bought it over a year ago, and I love it. It's dialed in for PETG and makes flawless prints. I have it in an aluminum enclosure with temperature monitoring. I also have a second Prusa MK3 that I adopted from another project and it was assembled by some students. I've run into countless issues with the printer, nearly all of them calibration-related from parts being too tight or too loose.
For this second printer, what do you all recommend to get it working properly? I was thinking about buying new belts and tearing it all down to parts, then re-assembling it from the ground up. That's obviously a major undertaking- does it make sense? I'm curious if anyone has run into this from getting a used or poorly-assembled printer.
Thank you in advance,
Jay
RE: Adopted 2nd Prusa MK3 continuing issues... next steps?
Belts are a strange thing to replace... They really don't wear, unless the students cut them the wrong length.
I would not tear down the extruder unless you have reason to. Visually observe all wires are routed correctly, with enough slack.
I would remove (or loosen) the belts, loosen the frame screws, and put the frame extensions on a surface plate.
Follow the assembly procedure for tightening to get the frame straight.
Same for the carriage.
Loosen the Z axis screws and use the assemble instructions to get the threaded rods parallel.
Visually inspect all the cables. Is the nylon rod installed correctly? No sharp flexing in use?
Check the heat bed screws. Connectors good - and tight.
As long as your machine is now dimensionally correct, I see no benefit to further disassembly.
Obviously the students plugged all the connectors in correctly, or it would not function at all.
After you finish, let us know any observed problems. We may have more suggestions.
RE: Adopted 2nd Prusa MK3 continuing issues... next steps?
@robert-rmm200
I just followed a forum post on how to tighten the Y-Axis belt, which was loose. Thank you for the detailed post- I have checked all of those things. What I have found is that every axis was loose, but I was troubleshooting them one at a time. Luckily I have fixed all the axis- and you were spot on with the heat bed connectors- I found that one first.
RE: Adopted 2nd Prusa MK3 continuing issues... next steps?
And make sure the belt drive gears are properly installed: if they are even slightly loose or not set in order, they'll give you problems in a month or two.
Flat First: Drive gears must be tightened flat-first.
1) Start with both set screws fully loosened so the pulley is free to spin on the motor shaft.
2) Align one set screw dead center with the flat on the motor shaft, slowly tighten the screw until it fully contacts the flat surface.
3) Torque the flat set screw to spec.
4) Now tighten the jam set screw, and torque it to spec.
Once tightened, never touch the flat set screw unless the jam screw is first fully loosened.
Why Flat First? Set screws have flat ends. If you tighten the jam screw first the set screw on the shaft flat doesn't fully contact the shaft, only one small edge of the screw surface is biting. Reversing torques can easily shift the shaft to a position the flat screw no longer contacts the shaft. This lets the jam screw wriggle loose. And after a while, vibration loosens the screws until the gear is free to rotate.