Lulzbot Mini 1 probing fails on last probe?

I had some issues recently with my thermistor in my bed - the cabling went bad. I replaced those two wires and I’m back in business, however, my new problem is, the bed no longer appears to recognize when the nozzle touches the last probe point.

Probe point washer 1: Taps fast, rises up, taps slow.
Probe poitn washer 2: Taps fast, rises up, taps slow.
Probe point washer 3: Taps fast, rises up, taps slow.
Probe point washer 4: Goes down and keeps going down past the point of the washer, pushing the bed down 1/8th of an inch briefly - rises back up - immediate octoprint error.
Erorr: Probing failed.
Send: M112
Send: N51 M11221
Send: N52 M104 T0 S0
Send: N53 M140 S0*83
Changing monitoring state from “Error” to “Offline after error”
Connection closed, closing down monitor
Changing monitoring state from “Offline” to “Opening serial connection”

Does each corner have it’s own grounding point and maybe the 4th washer isn’t properly connecting? Is the fourth washer just a tiny bit outside the bounds of auto-leveling?

I used a caliper and it’s 179.5mm from the top of the chassis to the top of the Z bar when it fails to probe on both sides of the X axis. So, the Z axis isn’t sagging or being weird.

It’s 82.5mm from the bottom of the bed to the desk on probe/washer 1. But it’s 83mm at all other 3 probe/washer points. Oddly it probes points 2, and 3 without problem - and 2 & 3 are equidistant to the desk as probe 4, which fails - so that’s why I was asking about a grounding possibility?

I recently updated my firmware from ancient (probably 2 or 3 years old) to the latest in Cura LulzBot edition which is currently I saved and returned my stepping and z offset as instructions stated. Maybe this new firmware is somehow the culprit? I’ve only had maybe 3 or 4 successful probing’s and prints started, but I stopped them when I realized how bad they were coming out. Perhaps the Jerk and Acc features in Cura 5.1.1 are the reason, as the layers shift are not flat and smooth, and seems like my Y belt was loose. I tightened the Y belt up, but now it will not successfully probe since tightening the Y belt… :frowning:

The bed itself has a bit of give to it - which I don’t know if it’s normal or not - I can move it a tiny bit by rotating it like a clock. But the rods seem stiff as can be and do not have the “give” that the bed has. The two printed pieces that slide around the rods so the belt can pull the bed on the Y axis appears to be the pieces that have a teensy bit of give around the rod, but maybe this is normal - asking for clarity as I don’t have anything to compare it too. Video here: 11.14.2022-00.45.33

Anyone have any ideas why the probing fails on washer 4 (back right corner), and perhaps if it’s normal for the bed to have some give to it?

Thanks everyone!

Try loosening and tightening the 4th washer and then give it a good cleaning with some isopropyl achohol and a scotchbrite pad or some very fine (2000+ grit) sandpaper. You can also clean the nozzle by heating it to the normal temperature of your filament + 10 degrees, turn the printer off (to avoid shorts) and use either a scotchbrite pad or a brass brush (must turn off printer to use this).

You might try giving the nozzle a quick swipe the the scotchbrite on the way to the 4th washer. I always had trouble with the Mini bed leveling using PLA. With ABS almost never a problem. I think the PLA will ooze a little bit even at the nozzle wipe temp thus providing a little insulation at contact point so the electrons can’t flow.