Toolchange (StealthChanger)

What happens between T1 in the GCode and the printer extruding from the new tool, plus how the NFC-loaded metadata flows in.

The mechanics

sequenceDiagram
    autonumber
    participant G as GCode (T1)
    participant K as Klipper
    participant TC as klipper-toolchanger
    participant T0 as T0 (active)
    participant T1 as T1 (next)

    G->>K: T1
    K->>TC: tool change requested
    TC->>TC: PRE_TOOL_CHANGE hook (user macro)
    TC->>T0: park sequence:<br/>Z hop, dock approach, latch release
    TC->>K: switch active extruder
    TC->>T1: pickup sequence:<br/>dock approach, latch engage, leave dock
    TC->>K: apply T1 offsets (X, Y, Z, rotation, PA)
    TC->>K: restore Z, resume planned motion
    TC->>TC: POST_TOOL_CHANGE hook (user macro)
    K-->>G: ok (continue print)

The choreography itself is entirely viesturz/klipper-toolchanger; this site doesn't try to re-document it.

Where NFC metadata enters

Both pre- and post-change hooks read from save_variables so per-tool filament settings travel with the toolchange. The fleet's canonical PA applier (NFC_APPLY_PA + _PA_DEFAULTS) is documented verbatim in save_variables → reading from macros.

For a toolchanger the same priority logic (spool-specific PA → per-material fallback → universal default) applies once per tool. The shape below extends NFC_APPLY_PA to per-tool keys — verify your extruder naming (extruder / extruder1 / …) matches your config before using:

Adapt to your config

The skeleton below uses the same three-tier priority as the single-tool NFC_APPLY_PA. Pull the per-material defaults from _PA_DEFAULTS (see reference), swap the nfc_* reads for nfc_t{N}_*, and pass EXTRUDER=… to SET_PRESSURE_ADVANCE. Real macros also need homing checks, error paths, and slicer hand-off that aren't shown.

[gcode_macro NFC_APPLY_PA_TOOL]
description: Apply per-tool PA from NFC scan with material fallback
gcode:
    {% set t = params.T|int %}
    {% set svv = printer.save_variables.variables %}
    {% set pa_stored = svv["nfc_t" + t|string + "_pressure_advance"] | default(-1.0) | float %}
    {% set material  = svv["nfc_t" + t|string + "_material"] | default("") | string | upper %}
    {% set defaults  = printer["gcode_macro _PA_DEFAULTS"] %}
    {% set extruder  = "extruder" if t == 0 else "extruder" + t|string %}

    {% if pa_stored > 0 %}
        SET_PRESSURE_ADVANCE EXTRUDER={extruder} ADVANCE={pa_stored}
    {% else %}
        {% if   material == "PLA"                    %} {% set pa_fb = defaults.pla      %}
        {% elif material == "PETG"                   %} {% set pa_fb = defaults.petg     %}
        {% elif material in ["ASA", "ABS"]           %} {% set pa_fb = defaults.asa      %}
        {% elif material == "TPU"                    %} {% set pa_fb = defaults.tpu      %}
        {% elif material == "PC"                     %} {% set pa_fb = defaults.pc       %}
        {% elif material in ["PA", "NYLON", "PA-CF"] %} {% set pa_fb = defaults.pa_nylon %}
        {% else                                      %} {% set pa_fb = defaults.default  %}
        {% endif %}
        SET_PRESSURE_ADVANCE EXTRUDER={extruder} ADVANCE={pa_fb}
    {% endif %}

Then call it from the toolchange and print-start hooks:

[gcode_macro POST_TOOL_CHANGE]
gcode:
    {% set t = printer.toolhead.extruder|replace("extruder","")|default("0") %}
    {% set t = (t or "0")|int %}
    NFC_APPLY_PA_TOOL T={t}

[gcode_macro PRINT_START]
gcode:
    # …homing, levelling, heat soak…
    {% for t in range(5) %}
        NFC_APPLY_PA_TOOL T={t}
    {% endfor %}
    # …prime line, first layer…

What can go wrong, and where the NFC stack helps

Failure mode	Without NFC	With NFC stack
Tool 3 is loaded with PETG, you forget to update slicer	Underextrusion / blobs from wrong PA + temp	Last-scanned spool's PA/temp applied automatically; mismatch shows in Mainsail preset name
Re-running a print after physically swapping a spool	Slicer-baked temps used (potentially wrong)	If M109/M190 are removed from slicer start gcode and replaced by nfc_t{N}_*-driven equivalents in PRINT_START, the right temps follow the spool
Pressure advance tuned per spool in Spoolman	Operator has to remember to copy values around	Spoolman → daemon → nfc_t{N}_pressure_advance → POST_TOOL_CHANGE

Known issue: Y clearance on close approach

Warning

With the current dock spacing, the close_y clearance in some toolchange macro variants is too small — tools can clip adjacent docks during the parking approach. Increase close_y in the toolchanger config until clearance is comfortable, then re-tune each tool's dock position. Pending fix in this fleet.