Z axis trying to home through print bed

This is VERY weird. My printer was working fine (there are issues with Octoprint getting bogus data from the SV04 and it not being reliable using the right extruder), but it was working.

Today, I fired it up and when homing, the thing tried to drive the extruder through the print bed. I can’t home Z as it crashes into the bed, the steppers thump mercilessly and I end up having to turn it off. I can raise Z several cm and if I try to home it from there and trip the touch sensor with my finger, it stops as I’d expect. It also homes if I slip one of the X axis setup plates where the sensor (and NOT the nozzle) will touch it.

It’s almost as though the touch sensor moved up a couple of millimeters or so. Any ideas? Oh and yes, it’s been reflashed. Mainboard firmware: V1.1.0, touchscreen: V2.0

You can’t home the right extruder, it doesn’t have a sensor

First, I never mentioned the right extruder and I wasn’t worried about it. I know it’s adjusted relative to the left extruder. What was happening was the Z axis (X gantry) was lowering all the way into the bed with the left extruder in the center of the bed and wasn’t low enough to trigger the BLTouch.

But here’s a follow up. What was actually happening is that the bed, for some reason, got stuck down on its springs to the point where the X gantry was actually hitting the physical bottom limit of travel before the BLTouch would trigger. I loosened up the leveling knobs under the bed, “unstuck” the springs and left the bed at its highest point. Then homing worked as expected. Went through the paper-leveling mechanism again and Voila!

To prevent this from happening again, I printed out a set of 5mm thick shims I found here:

and used them. This raises the bed about 5mm and consequently reduces the vertical limit of build volume, but it’s a good compromise and gives more “adjustability” to the bed as the leveling screws aren’t at the limit of their travel. Oh, and I reflashed the firmware using Bjoern70’s firmware. Works quite well.

So, problem solved. Weird, but eventually sorted out. Sheesh!