# T-slot extrusion

T-slot aluminium extrusion profiles with their real cross-sections, any length. Nine sections of the common 20, 30
and 40 mm series.

| `profile` | Section | Slot | Area, mm² | Reference model |
|---|---|---|---|---|
| `2020-B6` | 20 × 20 | B-type, 6 | 174.34 | Profile-20x20-B-Type_Slot6_A |
| `2020-I5` | 20 × 20 | I-type, 5 | 171.99 | Profile-20x20-I-Type_Slot5 |
| `2020-I5-ISP` | 20 × 20 | item-compatible, 5 | 181.70 | Profile_20x20_I_Type_Slot5 (Item_Compatible_Profiles) |
| `2040-B6` | 20 × 40 | B-type, 6 | 286.73 | Profile-20x40-B-Type_Slot6 |
| `3030-B8` | 30 × 30 | B-type, 8 | 313.82 | Profile-30x30-B-Type_Slot8 |
| `3030-HFS6` | 30 × 30 | Misumi HFS6, 8 | 335.11 | misumi_profile_hfs_serie6_w8_30x30 |
| `3060-B8` | 30 × 60 | B-type, 8 | 552.58 | Profile-30x60-B-Type_Slot8 |
| `4040L-I8` | 40 × 40 light | I-type, 8 | 657.01 | Profile-40x40L-I-Type_Slot8 |
| `4080L-I8` | 40 × 80 light | I-type, 8 | 1133.45 | Profile-40x80L-I-Type_Slot8-Body |

## Geometry

Each section is centred on the origin in the XY plane, its longer side along Y, and extruded along +Z by `length`.
The section is the reference model's own outline at mid-length, written in the recipe as a table (`PROFILES`, in
`part.py`): loops of lines and arcs (each arc by its two ends and its midpoint), the outside first, then the cavities
and bores.

## Parameters

| Parameter | Meaning |
|---|---|
| `profile` | the section (table above) |
| `length` | mm |
| `finish` | anodising colour, `clear` or `black` (appearance only) |

## Sources

There is no manufacturer drawing behind these sections: **the geometry was measured from the published reference
models** below. Each model's cross-section was cut at mid-length with OCCT and every edge read exactly (line ends;
each arc's ends and midpoint), centred on the section's bounding box and rounded to 0.0001 mm; the recipe re-draws
those outlines in its own code. Every preset is checked against its own reference model (the catalogue entry it comes
from): bounding box within 0.05 mm (0.5 % over 100 mm), volume within 2 %, section area within 2 % and the section
outline within 0.1 mm of the model's.

All models are from **FreeCAD-library** (https://github.com/FreeCAD/FreeCAD-library, commit 2e36ae32), licensed under
[CC-BY-3.0](https://creativecommons.org/licenses/by/3.0/) (the library's licence for all its parts), and distributed by
step.parts (https://www.step.parts, entries `profile_*`, identical geometry; its length variants `*_l50` to `*_l2000`
are the same sections). No endorsement by the authors or the FreeCAD project is implied.

- `Mechanical Parts/Profiles EN/Generic/Profile-20x20-B-Type_Slot6_A.step`, `Profile-20x20-I-Type_Slot5.step`,
  `Profile-20x40-B-Type_Slot6.step`, `Profile-30x30-B-Type_Slot8.step`, `Profile-30x60-B-Type_Slot8.step`,
  `Profile-40x40L-I-Type_Slot8.step`, `Profile-40x80L-I-Type_Slot8-Body.step`: by **mathis** (GitHub Int-Circuit).
- `Mechanical Parts/Profiles EN/Item_Compatible_Profiles/Profile_20x20_I_Type_Slot5.stp`: by **Stefan Katerkamp**.
- `Mechanical Parts/Profiles EN/Misumi_profiles/misumi_profile_hfs_serie6_w8_30x30.step`: by **Felipe Machado**.

Simplifications: the 40 × 80 model's eight spline edges are drawn as 16 chords each (within 0.01 mm); otherwise none
beyond the models' own (no end threads). The B-type and I-type models are generic sections of those slot systems;
makers' sections differ in detail, so check a specific maker's drawing where it matters.

The catalogue's `tslot_*_l0600` entries are step.parts' simplified stand-ins (a rectangle with one rectangular groove
per face), not T-slot sections, and are not presets. Preset list: from the step.parts catalogue (MIT), see
`library/NOTICE.md`; entries without a length (the base models) are presets at the model's own length.