# Tutorial 2 — Two Classic Mechanical Parts: a Flanged Bushing and an L-Bracket

> **Before you start:** do Tutorial 1 first (`starter-help-and-tutorial.md`). It covers the editor, `params`, and how Rebuild works.
> Every CADL listing below passes `dsl.validate` and builds to STEP with `design/dsl.py`. The measured results are noted under each listing. The AI may phrase its own result a little differently, but the structure will be the same.

**What you'll learn**
- **Part A:** a *turned* (round) part. You'll see two ways to build it, with stacked cylinders or with a single `revolve` profile, plus how to resize the bore and take the STEP file to CNC.
- **Part B:** a *multi-face* part. You'll drill holes from two different faces and learn how the hole `[u, v]` coordinates work on each face.

---

## Part A — Flanged Bronze Bushing (CNC lathe or 3D print)

### A1. Prompt
Set **Mode** to `CNC (3-axis)` if you'll machine it, or `3D print` if you'll print it. Then enter:
```text
Flanged bushing: 30 mm flange diameter, 4 mm flange thickness, 18 mm body outer diameter, 22 mm total height, with a 10 mm through bore and a 1 mm chamfer on the top edge
```
Click **Generate**. You should get **PASS** with a bbox of **30 × 30 × 22 mm**.

### A2. The CADL recipe (stacked cylinders + union + chamfer + hole)
```jsonc
{
  "units": "mm",
  "plan": "1. Flange: cylinder Ø30 x 4, base centred on the origin (z 0..4). 2. Body: cylinder Ø18 x 22 on the same axis (z 0..22), overlapping the flange. 3. Union. 4. 1 mm chamfer on the outer top edge of the body, picked by a point on that edge. 5. Ø10 bore drilled through all from the top.",
  "issues": [
    {"type": "assumption", "msg": "Only the outer top edge is chamfered; the bore edge stays sharp.", "ref": "top_chamfer"},
    {"type": "assumption", "msg": "The flange sits at the bottom (z = 0).", "ref": "flange"}
  ],
  "params": {"flange_d": 30, "flange_h": 4, "body_d": 18, "total_h": 22, "bore_d": 10, "chamfer": 1},
  "steps": [
    {"id": "flange", "op": "cylinder", "diameter": "$flange_d", "height": "$flange_h"},
    {"id": "body",   "op": "cylinder", "diameter": "$body_d",   "height": "$total_h"},
    {"id": "blank",  "op": "union", "items": ["flange", "body"]},
    {"id": "top_chamfer", "op": "chamfer", "target": "blank", "distance": "$chamfer",
     "edges": "near", "points": [["=$body_d/2", 0, "$total_h"]]},
    {"id": "bore", "op": "hole", "target": "top_chamfer", "face": "top", "diameter": "$bore_d", "positions": [[0, 0]]}
  ],
  "result": "bore"
}
```
**Measured:** bbox 30.00 × 30.00 × 22.00 mm, volume 5,652.8 mm³. The STEP file has 3 cylindrical faces, 3 flat faces and 1 cone (the chamfer).

**How the params work**

| Param | Meaning | Used by |
|---|---|---|
| `flange_d` | Flange outer diameter | `flange` |
| `flange_h` | Flange thickness (z 0..4) | `flange` |
| `body_d` | Body outer diameter | `body`, and the point that picks the chamfer edge |
| `total_h` | Overall height, flange included (the body runs from z = 0, so the total stays exact) | `body`, chamfer point |
| `bore_d` | Through-bore diameter | `bore` |
| `chamfer` | Chamfer size | `top_chamfer` |

**Why it's built this way**
- Cylinders default to `anchor: "base"`, so both start at z = 0 on the same axis. The body overlaps the flange instead of sitting on top of it. That keeps `total_h` truly the total height and gives the `union` a solid overlap.
- The chamfer uses `edges: "near"` with a point exactly on the outer top rim, `[body_d/2, 0, total_h]`. `edges: "top"` would also chamfer the bore rim, because every edge of the top face counts.
- The chamfer comes **before** the hole. At that point the top face has only one circular edge, so there's no ambiguity.
- The `hole` has no `depth`, so it goes through all. On `face: "top"`, `[0, 0]` is the global x, y of the axis.

**Alternative: one `revolve` profile** (identical solid, also 5,652.8 mm³). Use this when you want the whole cross-section in one place:
```jsonc
{"units": "mm",
 "params": {"flange_d": 30, "flange_h": 4, "body_d": 18, "total_h": 22, "bore_d": 10, "chamfer": 1},
 "steps": [{"id": "bushing", "op": "revolve", "profile": [
   ["=$bore_d/2", 0], ["=$flange_d/2", 0], ["=$flange_d/2", "$flange_h"], ["=$body_d/2", "$flange_h"],
   ["=$body_d/2", "=$total_h-$chamfer"], ["=$body_d/2-$chamfer", "$total_h"], ["=$bore_d/2", "$total_h"]]}],
 "result": "bushing"}
```
The profile is a list of `[r, z]` points: radius out from the Z axis, and height. Starting at `r = bore_d/2` instead of 0 leaves the bore hollow, and the diagonal point pair is the chamfer.

### A3. Open up the bore: 10 → 12 mm (no AI)
1. In `params`, change `"bore_d": 10` to `"bore_d": 12`.
2. Click **Rebuild (no LLM)** or press **Ctrl+Enter**.
3. Check the result: the bbox stays 30 × 30 × 22 and the volume drops to **4,892.5 mm³**. If the bore were bigger than `body_d - 2*chamfer`, the build would fail and a red error line would appear. Click it to jump to the problem.

### A4. To CNC: STEP → CAM → feeds & speeds → simulate
1. Download **part.step**. It holds true cylinders and a true cone, which CAM needs for clean toolpaths. Open it in Fusion, FreeCAD Path or another CAM program.
2. Work out spindle speed and feed for bronze (e.g. 932/SAE 660 bearing bronze) and your tool in the **Feeds & Speeds** calculator at [spinstop.com/engine/](https://spinstop.com/engine/).
3. Post-process to G-code and load it into **G-code Sim** at [/gsim/](https://spinstop.com/gsim/) with **Open file**, or with **Save to account** and **My programs…**. Pick a flavor (e.g. *milling (LinuxCNC)*), choose *path + stock*, and press ▶. You can color the path by speed to spot slow moves.
4. *If you're 3D printing instead:* click **Save to account → Open in Mesh / Slicer → Slice to G-code → Open in Simulator**.

> ⚠️ gsim simulates milling and printer G-code. It does not show lathe (turning) toolpaths, so check lathe code in your CAM program.

---

## Part B — L-Bracket with Holes in Two Faces

### B1. Prompt
```text
L-bracket 50 mm wide, base leg 60 mm long and 6 mm thick, vertical wall 45 mm tall and 6 mm thick, with two 5 mm holes in the base and two 5 mm holes in the vertical wall
```
You should get **PASS** with a bbox of **60 × 50 × 45 mm**.

### B2. The CADL recipe (box + box + union + hole on top + hole on left)
```jsonc
{
  "units": "mm",
  "plan": "1. Base: box 60(x) x 50(y) x 6(z) with its corner at the origin. 2. Wall: box 6 x 50 x 45 with its corner at the origin, so it overlaps the base at x 0..6, z 0..6. 3. Union. 4. Two Ø5 holes down through the base from the top face at x=38, y=12.5 and 37.5. 5. Two Ø5 holes through the wall from the left face (-X) at y=12.5 and 37.5, z=30.",
  "issues": [
    {"type": "assumption", "msg": "Base holes are at x = 38, 12.5 mm in from each side.", "ref": "$base_hole_x"},
    {"type": "assumption", "msg": "Wall holes are at z = 30 mm, well above the base.", "ref": "$wall_hole_z"}
  ],
  "params": {"w": 50, "base_l": 60, "t": 6, "wall_h": 45, "hole_d": 5, "edge": 12.5, "base_hole_x": 38, "wall_hole_z": 30},
  "steps": [
    {"id": "base",    "op": "box", "size": ["$base_l", "$w", "$t"],  "anchor": "corner"},
    {"id": "wall",    "op": "box", "size": ["$t", "$w", "$wall_h"],  "anchor": "corner"},
    {"id": "bracket", "op": "union", "items": ["base", "wall"]},
    {"id": "base_holes", "op": "hole", "target": "bracket", "face": "top", "diameter": "$hole_d",
     "positions": [["$base_hole_x", "$edge"], ["$base_hole_x", "=$w-$edge"]]},
    {"id": "wall_holes", "op": "hole", "target": "base_holes", "face": "left", "diameter": "$hole_d",
     "positions": [["$edge", "$wall_hole_z"], ["=$w-$edge", "$wall_hole_z"]]}
  ],
  "result": "wall_holes"
}
```
**Measured:** bbox 60.00 × 50.00 × 45.00 mm, volume 29,228.8 mm³. The STEP file has 4 cylindrical faces (the four holes).

### B3. How `[u, v]` works on each face
A hole's `face` sets the drilling direction. Its `positions` are **global coordinates in mm** on the two other axes:

| `face` | Side of the target's bbox | Drills along | `u` | `v` |
|---|---|---|---|---|
| `top` / `bottom` | +Z / −Z | Z | x | y |
| `front` / `back` | −Y / +Y | Y | x | z |
| `left` / `right` | −X / +X | X | y | z |

- **Base holes (`face: "top"`).** `[38, 12.5]` means x = 38, y = 12.5. "Top" means the top of the *whole* bracket's bbox (z = 45, the top of the wall). Because a hole with no `depth` goes through all, it still cuts cleanly down through the 6 mm base. Keep `base_hole_x` greater than `t` (6), or you'll drill into the wall.
- **Wall holes (`face: "left"`).** The wall is the −X side of the bbox (x 0..6), so `[12.5, 30]` means y = 12.5, z = 30. Keep `wall_hole_z` greater than `t`, or you'll hit the base.
- *Why not `front`?* The front (−Y) face is the 50 mm *edge* of the L, so holes from there would run lengthwise through the part. Pick the face whose normal is the hole's axis.

### B4. Try these edits (Rebuild, no AI)
- `"hole_d": 5` → `5.5` for M5 clearance.
- `"wall_h": 45` → `60`. The wall grows, and the wall holes stay at `wall_hole_z`. You could make that a formula: `"wall_hole_z": "=$wall_h*2/3"`.
- `"t": 6` → `8`. The base and the wall both thicken, because both boxes use `$t`.
- *With AI:* type `add a 5 mm inside fillet where the base meets the wall` in **Edit with AI**. The usual result is a `fillet` step (`"edges": "near", "points": [[6, 25, 6]]`, radius 5) placed before the holes. This version was checked and builds.

### B5. Export
**part.step** for CAD/CAM. **part.stl → Open in Mesh / Slicer** for printing; print it on its side so the layers run along the bend for strength.

---

## 90-Second Video Storyboard — Tutorial 2

| Time | On screen | Voice-over |
|---|---|---|
| 0:00–0:06 | Title card: bushing + L-bracket renders | "Two classic shop parts: a flanged bushing and an L-bracket." |
| 0:06–0:18 | Paste the bushing prompt, Mode = CNC, Generate, PASS 30×30×22 | "Give every diameter and height, including the chamfer. Generate." |
| 0:18–0:30 | CADL editor: highlight `flange_d … bore_d`, then the steps | "Two cylinders, a union, a chamfer on the outer rim, and a through bore. Every size is a named param." |
| 0:30–0:40 | `bore_d` 10 → 12, Ctrl+Enter, bore widens, volume updates | "Need a 12 mm bore? Change one number and rebuild. No AI needed." |
| 0:40–0:48 | Click part.step; /engine/ feeds & speeds; /gsim/ path playing | "Take the STEP file to CAM, check feeds and speeds, and simulate the G-code." |
| 0:48–0:58 | Paste the L-bracket prompt, Generate, rotate the bracket | "Now an L-bracket with holes in two different faces." |
| 0:58–1:12 | Overlay the face/axis diagram; highlight `face: "top"` [x,y] and `face: "left"` [y,z] | "Holes on the top use x and y. Holes on the left wall use y and z. It's always global millimetres." |
| 1:12–1:22 | `t` 6 → 8 and Rebuild; then Edit with AI "add a 5 mm inside fillet" | "Thicken both legs with one param, or ask the AI for a fillet." |
| 1:22–1:30 | Open in Mesh / Slicer → Slice → Simulator | "Slice it, simulate it, make it. Quick-start and help links are below." |