alarm 8 while auto-squaring Y axis

[d-granger]

I have a CNC gantry router with dual Y axes. I used the grblHAL web builder to configure my kernel with 3 axes, auto-squared. I have my limits placed in the same fashion as in Phil's blog on auto-squaring (min and max on Y and min only on A). I'm using 24v NO NPN prox sensors for limits so I have an 8 chan opto-isolated level shifting board between the sensors and the limit inputs to the BOB. The second Y axis limit is connected to the A limit on the BOB. I inverted the limits for XYZ in ioSender. Hard limits are enabled as is homing via ioSender.

Manually tripping the limits shows that A is indeed coupled to Y as ioSender shows Y as tripped when I trigger A. My level-shifting board has indicator leds on each channel and shows that the signal is coming in on the A limit.

When I home, Z is successful as is X, then the Y axis moves to the minimum position until both Y & A limits trip (leds on both sensors and both inputs on opto board light), and ioSender raises an Alarm 8 & halts leaving both limits tripped. I adjusted my limit stops so Y tripped before A and vice versa, and the behavior repeats in both cases.

Any idea on how to remedy this?

[phil-barrett]

Increase pull off distance? I think the default is 1mm. It needs to be large enough to untrigger the sensor. I'd start with 5mm.

[d-granger]

Thank you!

The magic distance was 1.5mm. I obviously haven't calibrated my squaring and hope that once I have it dialed in I won't be needing a large pull off. I was careful during construction to square the frame but I'm sure there will still be some offset between the 2 rails. Thanks again.

[phil-barrett]

1.5mm is not bad at all. Also, if you increase the search seek rate ($25), you will get more overshoot and will have to increase the back off distance.

[d-granger]

I bumped my search seek to 1500mm/sec so I expect that there is some overshoot from that. I still hope that my Y and A are pretty close since I was careful about getting things square during the mechanical build.