Manual Toolchange + Abs Z Probe (QtDragon)

I'd like to share a structured and slightly modified version of `qt_auto_probe_tool.ngc` I'm using on my self-built 3-axis CNC with LinuxCNC 2.9.3 and the QtDragon GUI.  

---

### ? My Goals:
- Separate tool length offset from work coordinate systems (WCS)
- Make the tool table intuitive and readable
- Ensure safe and efficient probing using machine coordinates

---

#### 1. Set the Probe Top:
I defined the probe top using the tip of the spindle body (with no tool/collet) as a consistent mechanical reference.

- For example, if the empty spindle is lowered to Z = -120 (machine coordinates), I input `-120` as PROBE HT in the QtDragon Probe tab.(I know this is not the intended use.)
- I do not use BLOCK HT at all.

#### 2. Define Work Coordinates:
Once a tool is mounted (e.g., Tool #1 with 30mm protrusion), I:
- Add `T1 Z30` into the tool table
- Set up the G54 (or other WCS) normally

This way, the tool length stored in the table is actual physical protrusion and independent from any WCS — much more intuitive for manual tool changers.

Use G43 to apply the offset.

---

- Tool table values are stable and logical (they represent actual tool lengths).
- Easy to estimate and input values for new tools before probing.
- Tool probing uses machine coordinates, so:
  - Probe start position can be calculated from tool length
  - No dependency on current WCS
  - Safer: if tool table Z is negative by mistake, start offset is clamped to zero
- Multi-WCS workflows (G54, G55...) work seamlessly — no need to re-probe per WCS
- Tool probing is simpler and can be single-pass since start is close

---

Thanks,  

SanzuiWorks

I created a diagram so that the offset value can be visually confirmed.

In the conventional method, if the table bottom is always set to G54_Z0, there is no problem with setting [BLOCK HT], but if the work top is set to WCS, [BLOCK HT] must be changed frequently.
Changing is troublesome, and checking the current setting value is also cumbersome.
If the WCS or [BLOCK HT] changes, the tool table value also changes.
Also, I cannot read what the offset value in the tool table indicates.

---

After the change,
Z height can be set in WCS as well as XY,
so the situation can be checked from the main screen.
In particular, the Z height is consistent, and is reflected when the WCS is switched.

The tool is always consistent with positive compensation.
The Z_offset in the tool table is easy to read because it lists the tool length.

Since the tool offset is consistent, it can be approached at high speed in advance when probing. This is expected to reduce probe time, especially on slow-moving machines.
If the previous tool length could be displayed in the tool change dialog, human error would also be reduced.

So far we haven't had any major issues,
but we'd like other people to take an interest and find ways to improve it.

I had been using it without much thought, but it seems better to remove G43H0 G54.
The tool length offset is unintentionally canceled, and the work coordinate system switches."

Reading Work Coordinates When Loading a New NGC File  

When loading a new `.ngc` file in LinuxCNC, is it possible to read the work coordinates at that stage? Since the G-code has not been executed yet, the work coordinates might not be applied.  

Would it be possible to create a custom button, similar to "WCS Sync," that reads the `.ngc` file and sends commands like `G55` to MDI?  

Has anyone implemented something similar, or does LinuxCNC provide a built-in way to achieve this? Any insights or suggestions would be greatly appreciated.

Thanks!

Can you post the changes you made?