Capacative leveling reading different over areas of the build plate?

I’m using a standard TAZ5 build plate, no mods. I installed a capacative auto-leveling system recently and it’s been working great.

I went to do some tweaks to it, which resulted in the locations measured to be different than they had been, and on 2 spots on the bed (from a 3x3 grid of leveling) the sensor didn’t activate at all, even after the safety physical limit switch had been triggered. I just spent forever trying to figure out the problem, cleaned the bed, remounted and recalibrated the sensor, everything. It worked fine on all the tests I did - until the auto-level ran again.

It was then than I realized the auto-level keeps running the tests in the same spots. So I made sure the sensor was calibrated, then moved it to the same X/Y position, and did a manual Z level. Like the G29 auto level, it overshot and hit the bed.

I then played with position, and found out if I moved the bed back just 5mm, it leveled fine. If I brought it forward 4mm, the sensor didn’t activate. If I sent it forward another 20mm, the sensor worked.

I always autolevel with the heat on, to take into account expansion. I’m wondering if it’s a cold spot on the bed? Or maybe the sensor is picking up the wiring from the heater and thats a dead space? Is there a diagram of the wiring layout anywhere I can reference?

Anyone experienced this themselves?

If you turn the bed around, you can see the layout of the nichrome wiring layout.

I just happen to have a bed disassembled from the aluminum carriage… I’ll try to post pics tonight.

If your sensor is only detecting the metal wire, you may not have a capacitive probeinductive probes sense metal. Quick test would be to watch the LED and move the toolhead over the surface of the bed manually.

If you do have an inductive bed sensor, one way to fix that would be to order and install steel foil tape on the underside of the bed. It may give you enough signal to trigger. The stuff is rediculously expensive though, and the aluminum foil stuff is too thin. Copper foil might also work if you can find it.

The other option is to go for the aluminum build plate upgrade, which will improve your overall bed adhesion and give you something conductive for the sensor.

Except, it’s not inductive.