Does bed leveling use z probe offset? Can't get it to work

Hello, I built an arduino/ramps/2130/p3 steel printer. I had it working, but I reconfigured it this morning, eliminating the glass (BuildTak sheet on heat bed) and converted it from an inductive sensor to a smaller IR sensor. I've wasted HOURS trying to get this to work as I assume it should.

I've gone through the calibration steps 100x: M851 Z0 to reset z offset, G28, G1 X95 Y95, M211 S0 to turn off software endstops, manually move tip down until paper just touches (stop detects at about 2mm, and I keep going). M851 Z-2.19 to store new offset, M500 to store to EEPROM and finally M211 S1 to enable end stops. If I then issue G29 for tramming, it going through my three points, but it doesn't go anywhere near low enough for the sensor to detect the bed. So what's the point if it stops at 0, instead 0 - 2.19? It can't be collecting any data w/o sensor feedback, so what does it think it's doing? Am I misunderstanding what the goal of G29 is?

Thanks.

Just set your z min software endstop to - 4mm then hit G29. You can always set it to something more reasonable like -0.2mm afterwards.

There was a change in marlin around 1.1.0 when the way software endstops or travel limits are handled. So they don't always turn on and off as you would expect Eg send a G92 command which would allow movement beyond the travel limits and the movement won't be allowed. I can see the argument for this in a production machine but for a hobbyist machine it seems a little too safe.

Edited 2 time(s). Last edit at 03/11/2018 11:00AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

To be honest, I'm not completely following you, but ...

I made some good progress. I discovered that my IR sensor was not seeing the arduino controlled pull-up on the sensor OUT pin and was initializing in analog mode. This means it was sending an analog measurement and who knows how that was being handled when Marlin was expecting a bit. I had to add a physical pull-up and now the sensor seems to be working correctly.

Thank you.