[Solved] Added MMU2S, now the fan touches the bed
I have a Prusa Mk3 with the MMU2S kit. The MMU came with a new part-cooler fan mount and duct. With these mounted, the fan is now lower than the nozzle.
Has anyone else experienced this? Do I have a subtly-incompatible model of the Mk3? I'm not sure why the new parts were included, so I don't know if I should try to keep them, go back to the old ones, or (design and?) print new parts that actually fit.
The bottom of the fan duct (fan-shroud) should be parallel with the bed, not angled down like it is in your photo. Check that the print fan is properly aligned into it; perhaps it's being forced down by the fan. Check that the print-fan-support (bar that holds the top bolt of the print fan) is properly installed.
Here's how the whole assembly looks:
Looks alright to me, but I started by removing the fan. There wasn't any tension in the assembly, and the duct didn't move when I removed the fan.
I removed the duct next, and discovered that one corner of it has been melted.
I looked at how it is held in the assembly (by just 1 screw, which also holds the hotend cooler fan onto the side of the extruder). When screwed in, the duct is held far enough to one side that it is pressed firmly against the heater block.
Maybe a spacer could hold it off the fan mount, centering the duct on the heater block? But no, it turns out that the duct is too narrow to accommodate the heater block even if perfectly centered on it.
I'm not sure how this is supposed to work at all...
You were right. I've never assembled or disassembled the Prusa extruder before; it hadn't occurred to me that it might have been assembled incorrectly.
I removed the two screws on the back holding the motor in, and the two screws below the motor holding the front of the hotend shroud on. The hotend was just sitting in a recess in the remaining printed pieces. I pulled some slack out of the cable sleeve, rotated it 90 degrees, and held it there while I screwed the extruder back together.
Now that the duct isn't touching the hotend, it is level and above the height of the nozzle.
Glad I could point you in the correct direction!