# KiCad → Stencil G-code pipeline

Automates the conversion of a KiCad v9 `F.Paste` and `B.Paste` Gerber to G-code for CNC milling a solder paste stencil, using FlatCAM beta 8.995 headless. Tested on Ubuntu 24.04 with Python 3.12 and a Frezu 3040 / FluidNC controller.

---

## Prerequisites

- Ubuntu 24.04
- Python 3.10–3.12
- KiCad v9
- A flat end mill (corn bit), 0.5 mm recommended

---

## Installation

### 1. System dependencies

```bash
sudo apt install python3-venv python3-pip libgeos-dev libspatialindex-dev libxcb-cursor0
```

### 2. Clone FlatCAM beta 8.995

```bash
git clone --branch mstanciu_Beta_8.995 --depth 1 https://github.com/dwrobel/flatcam.git flatcam-beta
```

### 3. Create a Python venv and install dependencies

```bash
cd flatcam-beta

python3 -m venv .flatcam-env
source .flatcam-env/bin/activate

pip install PyQt6 PyQt6-Qt6 PyQt6-sip

# Skip ortools (path optimizer), rasterio, and gdal (image import) — not needed for stencils
grep -vE "ortools|rasterio|gdal" requirements.txt | pip install -r /dev/stdin
```

### 4. Verify

```bash
python flatcam.py --version
```

You should see the FlatCAM version string printed without errors.

Go back to the project directory:
```bash
cd ..
```

### 5. Export the stencil gerbers

Export the gerber layers `F.Paste` and `B.Paste`
```bash
kicad-cli pcb export gerbers -o gerbers -l F.Paste,B.Paste ../kicad2panel/panel/Flow_Controller_Panel.kicad_pcb
```

---

## Usage

Generate the stencil G-code for both layers:
```bash
./run_stencil.sh gerbers/Flow_Controller_Panel-F_Paste.gtp \
                 gcode/Flow_Controller_Panel-F_Paste-stencil.nc

./run_stencil.sh gerbers/Flow_Controller_Panel-B_Paste.gbp \
                 gcode/Flow_Controller_Panel-B_Paste-stencil.nc
```

G-code for both layers should be in:

```
gcode/Flow_Controller_Panel-F_Paste-stencil.nc
gcode/Flow_Controller_Panel-B_Paste-stencil.nc
```

---

## Parameters

All cutting parameters are at the top of `paste_stencil.tcl`:

| Variable | Default | Description |
|---|---|---|
| `TOOL_DIA` | `0.5` | End mill diameter in mm |
| `CUT_Z` | `-0.2` | Cutting depth in mm (negative). Set slightly past material thickness |
| `TRAVEL_Z` | `2.0` | Safe travel height in mm |
| `FEEDRATE` | `120` | XY feed rate in mm/min |
| `SPINDLE` | `15000` | Spindle speed in RPM |
| `OVERLAP` | `60` | Tool overlap in % — higher = cleaner clearing, more paths |
| `MARGIN` | `0.0` | Inset from aperture edge in mm. 0 = cut to exact pad size |

### Depth by material

| Material | Thickness | `CUT_Z` | `SPINDLE` | `FEEDRATE` |
|---|---|---|---|---|
| Brass shim (CW614N) | 0.15 mm | -0.18 | 24000 RPM | 120 mm/min |
| Polyimide (Kapton) | 0.10 mm | -0.13 | 24000 RPM | 300 mm/min |
| Stainless steel shim | 0.15 mm | -0.18 | 16000 RPM | 60 mm/min |

---

## Preprocessor

The script uses the `GRBL_11` preprocessor (`-pp GRBL_11` in `paste_stencil.tcl`), which produces grbl 1.1 compatible G-code. FluidNC implements the grbl protocol so this works directly with no modifications.

Alternative: `GRBL_11_no_M6` suppresses tool change commands — not needed for a single-tool stencil job but harmless either way.

---

## Workholding notes

- Stencil material is thin and will flex — use double-sided tape on a flat spoilboard
- Zero Z directly on the stencil surface, not the spoilboard
- For brass shim, clamp the edges with small clips if the tape isn't holding — chatter from an unanchored sheet ruins aperture quality

---

## Troubleshooting

**FlatCAM hangs after writing G-code**
The `run_stencil.sh` wrapper detects the `TclCommandQuit` log line and kills the process after 3 seconds. This is expected behavior — FlatCAM's Qt GUI cleanup hangs in headless mode.

**`ImportError: cannot import name 'Inf' from numpy`**
You have the old PyPI FlatCAM 8.5 installed. Follow the installation steps above to switch to the beta 8.995 clone.

**`ImportError: cannot import name 'cascaded_union' from shapely.ops`**
Same cause — old FlatCAM 8.5 is incompatible with Shapely 2.0. Switch to beta 8.995.

**G-code cuts everything except the pads**
You used `ncc` (non-copper clear) instead of `paint`. The correct command is `paint` — it pockets the pad polygons. `ncc` clears everything around them, which is the inverse.

**`gdal` fails to install**
Skip it — `gdal` is only needed for the image import plugin. Use:
```bash
grep -vE "ortools|rasterio|gdal" requirements.txt | pip install -r /dev/stdin
```