Heads up - the dual head printer can start "printing" without filament loaded
Not a world ending problem but worth being aware of. There is at least one condition where the dual head Prusa XL will try to run a print job with no filament loaded in the tool.
I unloaded filament from Tool 2 but did not reload filament into Tool 2. I then started a print file sliced for a single tool expecting it to select Tool 1. Tool 2 was still in the carriage when I started the print, as the machine had left it there following filament change. The printer went through the full pre-print routine with Tool 2 still in the carriage. It then started the print, even though there was no filament in the tool. At no time did I get a warning that there was no filament in Tool 2. The gcode was sliced for a single tool printer and I had expected it to automatically revert to Tool 1 when I started the print. In any case, I would have expected the filament sensor to recognize the absence of filament and at least asked for filament to be loaded before the print started.
It is probably unusual to unload filament and not reload at the time, but in this instance I wanted to unload the filament in Tool 2 to dry it and decided to run a single tool job while it was in the dryer.
RE: Heads up - the dual head printer can start "printing" without filament loaded
I could be mistaken, but I believe the MMU2 on the MK3 would do this, too. I can't confirm, as I've removed the MMU2 from my unit. My workaround was to always slice as a multi-tool printer and select the primary tool for my object.
RE: Heads up - the dual head printer can start "printing" without filament loaded
My workaround is to be sure I have selected a tool with filament before starting the print. It was a highlighted improvement with the 4.7.1 firmware that we could select which tool to use when starting a file sliced for a single tool printer. But with two filament sensors, both having no filament, I would expect the printer to report an error and refuse to print, so I believe the firmware needs to address this situation.
RE: Heads up - the dual head printer can start "printing" without filament loaded
If you dock tool 2 first it will pick tool 1 if it is a single tool in the gcode
RE: Heads up - the dual head printer can start "printing" without filament loaded
I just ran into this too. Dual-head XL, set for Spool Join, printing off of the thumbdrive.
My filament had some serious contamination in it - small flakes of something in it had it so wide that it didn't fit into the top of the Nextruder head. I unloaded the filament from both heads and replaced it with something else. I think on head 2, I had removed the filament without the proper "unload filament" procedure, probably figuring that having no filament present at both sensors would take care of things later.
It did not. I'd figured it might say "hey I have no filament anywhere. Want to load some more?" Nope.
Filament ran out on the first head, and the printer grabbed the still-empty second head, and started printing. I had to pause it and then load filament.
So, yeah, there's a condition or two where it'll go right ahead and print even with no filament present.
I double-checked too: The Filament Sensor is turned on.