Today I learned that when you “home” the build plate (Z axis) on the U1, it goes to the TOP of the enclosure, whereas the J1 homes to the bottom. That was quite a surprise!
The gory details: I had to leave the house as a print was in progress. While away, I decided to have a peek at the finished product. The model wasn’t visible in the camera’s field of view, so, I decided to move the bed up a bit to get it into view. However, U1 wouldn’t let me move the bed until it was “homed”, first. No biggie, right? So, I pressed “home”, then watched in horror as the hotend carrier positioned itself over the middle of the build plate, where the model is, and the build plate started moving UP!!!
It was like watching a train wreck in slow motion (well, not quite THAT bad, but still…). Once you give the “home” command, there’s no way to stop it, is there? So, I watched the bed try to move to the Z=0 position, while the printed model got jammed up against the underside of the hotend carrier. It wasn’t that hard to get the model out, once I got home later.
I’m starting a new print, now, without recalibrating the bed position. We’ll see how it goes!
I never had a J1, but every printer I had defined “home” as “nozzle on bed” (either in a corner or in the center). To me it seems the J1 is the odd one out here…
Indeed. It appears that, once a print is completed, you cannot move the build plate, without “homing” it first. Which, you can’t do if there’s a print on the plate. So, unless the finished print is very tall, you won’t be able to see it unless you go to the printer itself.
It would be really great if one could abort the homing routine (but I know that’s difficult to implement, because it’s a single command processed by the printer on its own, kind of “fire&forget”).
Yeah… if ever you need to home only XY, there’s a button to do so on the fluidd web interface. But not on the printer’s screen which is, yeah, “Home All.”
For what it’s worth, I made the same mistake once early on and quickly shut off the printer to not crush anything.
You’ll know this, but yeah, fundamentally different hardware. The J1s has a z limit switch at the bottom of travel. The U1 uses the print head to detect exact z location of the bed.
AFAICT, the printer is undamaged. I would certainly hope that it is robust enough to withstand an error like that! Anyway, I do have another print going, and all seems to be OK, though I have not yet closely inspected the result. I did NOT repeat any of the calibration steps before starting the new print, to see if any of the calibrations were knocked out of adjustment.
On a side note, I find the U1’s bed leveling mesh routine to be very helpful. The J1 only has a single Z-axis screw, and the build plate is only supported along the back edge, so I always had issues with layer shifts, and the bed not being completely level everywhere. The U1, with 3 Z-axis screws, and bed levelling at multiple points, is way better!
Just a follow-up. I’ve done several more prints since the “crashing the model into the print head” incident, without re-calibrating, and everything is fine.
It occurred to me that, as the U1 has the ability to detect when there is an object on the build plate, it might be worthwhile to include that check before the homing command is executed? I can’t imagine a scenario where you would want to Home while there is a model on the build plate.
