Odd print failure
On MK3S with 3.7.1 firmware: Has anyone else seen the issue where the filament sensor causes the printer to fail to print anything? It does the mesh bed check, heads over to the home position, lifts to about 40mm, goes about 2/3rds of the way across the bed on the X-axis and then wants me to unload the filament. When I unload it (which it does successfully), it asks me to reload it (which, after trimming the end of the filament, it also does successfully). The process then repeats indefinitely. Mesh level again, home again, lift, x-axis to 2/3rds, unload, etc. The result is that it doesn't print anything at all. Which I'm going to call a print failure.
I am absolutely sure that my magnets are in correctly, and that the little arm that gets pushed out of the way by the steel ball is loose enough to move easily. I'm also pretty sure sure the sensor is positioned properly (1 screw and only goes in 1 way), and wired properly (matches the pictures at the E-axis end, and correctly in the bottom row with the plug spacer in place (and the MMU plug in the top row so it has even fewer places to go wrong).
After several rounds of settings changes I isolated the issue to be caused by setting the filament sensor to on. I further confirmed that auto-load filament setting doesn't change the outcome since it does what I describe above regardless of whether auto-load is on or off. (At first I thought it was an issue with the auto-load feature, but it turned out to not be directly related.)
Anyone have any other theories about how I could have messed up the E-axis rebuild in a way that makes the filament sensor sad? It won't matter for long, I'm printing the MMU2S parts for the E-Axis now which includes the new placement for the filament sensor in the little tower thing that watches for movement on the idler door instead. That does not however stop me from being really curious about what theories are out there for what went wrong for me.
RE: Odd print failure
Don't expect the sensor tower for the MMU to make your life easier. Go read the active topics in the MMU forum and you'll see the tower has not be kind to some of us.
In fact what I would suggest that you do is print and install the tower first and then work on printing remaining parts as this will give you a chance to make sure you've gotten your IR sensor under control. If you can not successfully use the IR sensor as a plain MK3S I can promise you that you will be in for lots of trouble with the MMU.
If you are definitely doing the MMU upgrade, then I personally wouldn't bother troubleshooting your sensor as it stands now. Just make sure a print won't run out of filament 😀 Also I went from the MK3 to the MMU2S, so I have no experience with the plain MK3S IR setup.
For the MMU some have had issues with the pre-printed (don't know if there are issues with printing it yourself) door not properly tripping the sensor. Someone posted a minor modification that extends the tip a few mm to allow for fine tuning.
While I had done all the setup for aligning the tower and the sensor appeared to correctly report the presence of filament when I stuck it in, I couldn't get through any print without it demanding more filament if the sensor was on. What I expect was happening was that the movement of the printer was jostling the door/sensor just enough that it lost the IR read. I ran off that modified door and adjusted it until it seemed to be reading consistently. After than I haven't seen another false run out event since (about 6 days of almost solid printing).
Again, get everything on your printer playing happy as a plain MK3S with the MMU tower before you try to attach the MMU. That will help eliminate a whole raft of potential issues and complications.
RE: Odd print failure
Thanks for the feedback. I have never had good luck with the MMU2 and I ended up with a pure MK3s because I misinterpreted which parts to print for the MMU2S upgrade and which instructions to follow. (The good part was that the two misinterpretations were the same so when I was done, I had a functional MK3S without MMU2S to use for printing the other parts for the upgrade I'd failed to do at the same time.) Since I've fully upgraded all of my MK3 to an MK3S I've got nothing else to print at this point except the small part bundle with the tower in it. (I have printed all of the parts in question on my own and they have worked out excellently.)
In other words, I'm not in the camp that would ever assume the MMU makes my life easier. I'm glad to hear that you seem to have gotten past your sensor troubles.
RE: Odd print failure
Another suggestion I would offer (especially if space is limited) for the MMU is to skip their buffer and spool holders and instead print some auto-rewind spool holders. I ran the first two off single color without the MMU attached and the other 3 I've been doing through the MMU with the dial and clutch as the only dual color parts. If you time things right each holder takes about 24 hours (about 4 for the dual color dial and clutch, 14 for the blank stand and hub, and 7.5 for the rest of the parts (sans the useless arm)).
If space is tight, skip the long PTFE tube from the MMU to the spool. I found the curves were too tight and causing friction, so I switched to the short PTFE tubes in the back of the MMU and then left the filament loose from there to the spool. Friction on the filament movement appears to be bad and it doesn't seem to take much.
Between them and the door tweaking I was finally able to print a 2 color Benchy and 3 of the clutch and dial combos in dual color. Tonight I should be able to kick off a 5 color Benchy and see how that goes...