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    Why 0.7 Z offset in a probe?

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    • Danalundefined
      Danal
      last edited by Danal

      If I define a probe with M558, and then execute G31 (with no arguments), I see:

      G31
      Current reading 0, threshold 500, trigger height 0.700, offsets X0.0 Y0.0

      Why is the trigger height 0.7?

      I realize I can G31 K0 X0 Y0 Z0... but if I do that, and then undefine the probe and redefine it (which I'm doing to zero a toolchanger in different ways), it is back to 0.7. Again, I realize that undefining the probe 'uncouples' it from the G31, or the G31 'goes away' when the probe is undefined... I'm not asking why that happens... I am asking why 0.7 is wired in there somewhere.

      Why 0.7? Why not 0.0?

      This was very surprising to me, and took a really long time (months) to track down, simply because I couldn't imagine that a newly defined 'thing' in RepRap would have a fixed bias.

      Delta / Kossel printer fanatic

      spllgundefined 1 Reply Last reply Reply Quote 1
      • spllgundefined
        spllg @Danal
        last edited by

        @Danal i feel that defining g31 z0.25 in config.g has no effect. after a power cycle reboot g31 reports z =0.7. i'll check the effect of g31 z0.25 in config-override.g later today.

        Danalundefined 1 Reply Last reply Reply Quote 0
        • Danalundefined
          Danal @spllg
          last edited by Danal

          @spllg said in Why 0.7 Z offset in a probe?:

          @Danal i feel that defining g31 z0.25 in config.g has no effect. after a power cycle reboot g31 reports z =0.7. i'll check the effect of g31 z0.25 in config-override.g later today.

          At this moment, I have added a G31 K0 X0 Y0 Z0 in my config.g, and that does work across reboots, etc. Also, I dynamically re-define probes and endpoints in a script that is designed to calculate tool-to-tool alignment... and that script has been updated to issue G31 commands every time it redefines Z probes.

          Anyway, G31 in config.g is working for me.

          Delta / Kossel printer fanatic

          spllgundefined 1 Reply Last reply Reply Quote 0
          • spllgundefined
            spllg @Danal
            last edited by spllg

            @Danal Duet 3 6HC (v0.6) - RepRapFirmware 3.01-RC2 with RPi 4B - dwc 2.0.7-1?

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            • Danalundefined
              Danal
              last edited by

              Board: Duet 3 MB6HC (MB6HC)
              DSF Version: 1.2.4.0
              Firmware: RepRapFirmware for Duet 3 MB6HC v0.6 or 1.0 3.01-RC2 (2020-02-18b1)

              Duet Web Control 2.0.7

              Delta / Kossel printer fanatic

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              • Danalundefined
                Danal
                last edited by

                And, just checked, same thing on:

                Board: Duet WiFi 1.02 or later
                Firmware: RepRapFirmware for Duet 2 WiFi/Ethernet 2.05.1 (2020-02-09b1)
                Duet WiFi Server Version: 1.23

                Delta / Kossel printer fanatic

                spllgundefined 1 Reply Last reply Reply Quote 0
                • spllgundefined
                  spllg @Danal
                  last edited by

                  @Danal double checked: g31 z0.35 in config.g is ignored and g31 70.25 is honored when in config-overrige.g.

                  curretnly i'm unable to do any further tests/checks because of https://forum.duet3d.com/topic/14614/unable-to-home-xyz-using-my-homing-scripts

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                  • Danalundefined
                    Danal
                    last edited by

                    So after that nice discussion about G31...

                    Does anyone (hint: @DC42) know why probes have 0.7 Z offset, unless you override it?

                    Delta / Kossel printer fanatic

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                    • Danalundefined
                      Danal
                      last edited by

                      OK, the physical, literal, reason is this line of code in module "RepRapFirmware/src/Platform.h"

                      // Z PROBE
                      
                      constexpr float Z_PROBE_STOP_HEIGHT = 0.7;						// Millimetres
                      

                      But that begs the question: Why?

                      P.S. That module's header says:

                      Version 0.3
                      28 August 2013
                      Adrian Bowyer
                      RepRap Professional Ltd
                      http://reprappro.com

                      So maybe I should be asking Adrian.

                      Delta / Kossel printer fanatic

                      droftartsundefined 1 Reply Last reply Reply Quote 0
                      • droftartsundefined
                        droftarts administrators @Danal
                        last edited by

                        @Danal said in Why 0.7 Z offset in a probe?:

                        OK, the physical, literal, reason is this line of code in module "RepRapFirmware/src/Platform.h"

                        // Z PROBE
                        
                        constexpr float Z_PROBE_STOP_HEIGHT = 0.7;						// Millimetres
                        

                        But that begs the question: Why?

                        P.S. That module's header says:

                        Version 0.3
                        28 August 2013
                        Adrian Bowyer
                        RepRap Professional Ltd
                        http://reprappro.com

                        So maybe I should be asking Adrian.

                        It might be the value that was correct for the very first printer to use Duet, the RepRapPro Ormerod 1, which had an unmodulated IR sensor. I can't quite remember. But even that seems rather low.

                        Ian

                        Bed-slinger - Mini5+ WiFi/1LC | RRP Fisher v1 - D2 WiFi | Polargraph - D2 WiFi | TronXY X5S - 6HC/Roto | CNC router - 6HC | Tractus3D T1250 - D2 Eth

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                        • themelleundefined
                          themelle
                          last edited by

                          Got an answer from Adrian - for the curious ones 😉

                          1e3fc30b-1e35-4978-bca8-6afc5ced2f7b-image.png

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