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I need the correct offsets for FSR's mounted under the bed.

MShievitzMShievitz
in Extruder & Bed
I have the Utilbots FSR controller board connected to the z-min endstop.
the probe is normally low and triggers on high.
the offset for the probe is 0x,0y,0z which made sense to me, since the nozzle is, in effect the probe.
my hot end is either crashing into the bed and jittering around, or attempting to level much higher than the bed.
enough folks have this setup that i was hoping to find a sticky thread in the forums, but i can't find one.
the printer is otherwise calibrated pretty well and offsets have been taken care of, radius good, things track level, but i can't successfully use auto level commands.
the i have reset both the bump map and the leveling matrix.
the FSR's are very sensitive and working well, all states verified by m119 etc.

I remember seeing something like set your z-min to measured print height -2mm or setting your z-home to min, but i can't find those threads anymore.






Comments

  • RepetierRepetier
    What printer type do you have?

    Does the bed flex from the triggering force? In that case we have a bending correction that could help. Since they are force sensors you have some force to trigger them and that could cause bending. Also plastic can cause wrong signals. Always measure with hot hot-end so plastic makes no difference.
  • MShievitzMShievitz
    Well the bed does not flex, it's glass, but it's mounted on rubber discs that do compress. What you are suggesting might be the best way to go.
    But right now it's trying to level in the air. When I have been able to get it in contact with the bed, it drags across the glass below z0 and tries to pop up at the probe points. This type of set up has extremely small real offsets. Basically x0 y0 z-.025 or so. The probe is technically ABOVE the extruder tip by by a very small amount. I want the nozzle to drop from a safe distance say 5 mm, at each probe point push through the z0 plane, set the matrix at where the bed sensors were triggered -the offset , then pull back to that safe distance and move to the next probe point.
    The code, or at least my understanding of it is very "Allen key centric". It's fine to have the ball of an Allen key dragging across the bed when it's only being forced down by a ball point pen spring, but quite another to have the point of your nozzle digging into it driven by a trio of stepper motors.

    So what I need is the actual settings, for this type of setup.
  • RepetierRepetier
    Probes go back to start height. If you start higher then Z_PROBE_BED_DISTANCE it will go first down to that height and then start probing. With a reasonable value there you will never scratch between probes. Problem might be start height. You need to home to get it right, otherwise it assumes height when enabled = 0.

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