Probe offsets during probing



  • How do I configure the system correctly?

    My tool 0 nozzle is at (0,0)
    Probe is at (0,45)

    It seems like everything I do uses and reports the tool's position, not the probe's position.

    So, if I'm doing my tramming and the coordinate is (5,5), the probe is actually at (5,50) but the display shows the tool's position of (5,5).

    Where do I tell it my lead screws are? Relative to the tool or relative to the probe?

    Same strange behavior for Z homing. I have to offset the entire toolhead if I want the probe in the middle.

    I thought the whole point of configuring offsets is so that the control board can intelligently deal with them. I don't know how it can actually calculate anything if the values are all physical, but the probe is in a different place. That would make the plane fitting trig wrong.

    To make answering easier, let's assume the following.

    All coordinates are physical
    Bed is 300x300
    Lead screws are at (-30,150), (330,300), (330,0)
    Probe points are (0,0), (0,300), (300,300), (300,0)
    Probe offset is (0,45)



  • G31 uses the tools position but you have to consider the offset in your calculation.

    Example: If your printer has bed size of x 250mm and y210mm and your probe offset is x20 and y0 your mesh grid (M557) must start at x20 and stop at x230. (better to give it some more space so x25 and x225 is advisable)

    It's the same for the lead screws if you use G32 to trigger bed.g.

    Maybe you could post your config.g?



  • @Argo what does that mean, "it's the same for the lead screws"?

    You're confirming exactly what is confusing. If I switch tools from T0 to T1, the coordinates change based on the tool's offset. But when the probe is used, no such luck. So if, for example, I forget to switch back to T0, the behavior is multiple personality...

    If I Z home, the carriage realigns based on the tool position. But if I tram the bed, the carriage goes to the correct physical locations, but the coordinate display is offset.

    I guess it's technically correct that it always displays the "Head Position" if that means "tool position."

    But having to manually correct for offsets of the probe in some situations defeats much of the purpose of defining offsets.

    It makes me worry that if I probe a point at the same exact physical location, it can be T0 (100,100) or T1 (100,77) as they are the same place in space, the offset doesn't change, but the head position does, so I believe calculations area wrong if you accidentally leave any tool other than the main one selected.

    15905020660077598112279247407897.jpg



  • "what does that mean, "it's the same for the lead screws"?"

    It means that you need to keep in mind that your probe has an offset.
    For example: Offset is X20 and Y20. If you then use "G30 P1 X220 Y100 Z-99999 S2" for your 220 wide bed the nozzle won't be able to probe because it is most likely outside of your print bed because of the offset.

    It's a bit confusing at first though.



  • @Argo that's not what i'm asking. i'm asking, what coordinates should be used? It's not clear when offsets are being applied internally.

    if a lead screw is at y=300, the maximum reachable position for my probe. if i try to probe at y=300, it would crash the carriage as my probe is offset y+45. i have to tell it to probe at y=255 so my probe lands at y=300.

    i understand i have to keep track of that stuff, but i'm saying i shouldn't have to. the coordinate system is inconsistently behaved in terms of internal value vs. representation.



  • If I probe X150 Y150 to get a Z = 0 value I want this place to be probed and not somewhere else where my nozzle might be because this is later the place the nozzle prints.
    And it's easy to remember: G30, G31 use the offsets to get a accurate reading of the coordinates you want to measure for the nozzle.


  • administrators

    @gnydick said in Probe offsets during probing:

    Where do I tell it my lead screws are? Relative to the tool or relative to the probe?

    Everything (e.g. nozzle offsets, M208 machine limits, leadscrew positions) is measured relative to the Head Reference Point (HRP). It's up to you to decide where the HRP is. In a single-nozzle printer, it's normally chosen to be the position of the nozzle. On E3D tool changers, it's normally chosen to be the position of the Z probe, because that's fixed on the tool pickup whereas tools come and go and have different nozzle offsets.



  • So, when i give it a probe position, it puts the probe at the position indicated in the file, but the display shows the position according to the head position. E.g. Probe point = Y290, display = Y245 because the probe is Y+45.

    Makes it inconsistent.


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