Z Home Position - After I set offset, should G1Z0 go same location?
March 15, 2018 08:41AM
Trying to understand some fundamental concepts that I'm struggling with. Hoping someone could shed some light.

I have IR sensor on my arduino/I3 clone/RAMPs 1.4/Marlin that I built.

I home all axes, disable the software stop, zero out the z probe offset and sneak up a piece of paper under the tip. When in position I set the z probe offset to the difference (typically about -0.9) and re-enable the software endstops.

If I then issue G1Z0 the head goes up a bit. Also, if I home Z it seems to use the IR sensor to detect the bed and then goes to 10mm when done. If I then move down by 10 it returns to what appears to be the same spot as it does when I go to position 0, which again, is higher than the calibration spot.

Is this normal? Why isn't position 0 really position 0? Does Marlin somehow dip below 0 using the z probe offset when printing?
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