# Machine Contact Large

Adom **press-fit machine pin contact** (Large) for the Adom modular electronics
system. A machine **contact** (`MC`) is a receptacle pressed into a
plated through-hole on a molecule or scaffold. It accepts a machine **pin** (`MP`) tail, a
machine **needle**, or a bare wire, forming the solderless junction that ties molecules to
the workcell control panel and to each other on the 32mm scaffold grid. This page carries
the KiCad + Fusion 360 `.lbr` library, STEP, and an interactive 3D view.

## What it is and where it goes

Large machine contacts populate the **base scaffold** (an 18x18 grid of large contacts at
32mm pitch) and large-class molecules. Their role depends on where they sit. **On the base
scaffold they are purely mechanical** - that grid is not electrically connected, so the
contacts serve only as the mechanical mounting interface that molecules and scaffolds seat
into. **Everywhere else (molecules, user scaffolds) they are electromechanical** - carrying
power and signal between stacked boards in addition to providing the mechanical interface.
Large contacts are pressed directly into the board, and also press into the tops of large
machine pins so that pins, needles, and wires can be inserted into a stacked assembly.

## Rating and wiring

| Property | Value |
|---|---|
| Current rating | ~20.8 A (80% derated) |
| Mating wire | 14 AWG solid core (precision-bent, enamel-coated) |
| Mates with | Large machine pin tail (Ø1.85 mm), large needle, or 14 AWG solid-core wire |
| Grid pitch | 8 mm (technical); 32 mm is a common implementation (e.g. the base scaffold) |

The rating is contact-limited (a large machine pin can carry more, so the 20.8 A figure is
set by the contact) and is quoted at an **80% derating** for margin. The mating wire is
**solid core** (the enamel coating implies this, but it is called out explicitly).

## Mounting: press-fit into a plated through-hole

The contact presses into a **Ø2.62 mm plated through-hole** ringed by a **Ø4.40 mm** copper
annular pad. It is a solderless press-fit; solder-assist is available via the ring of 300um
jet-paste solder balls on the annular ring (Adom's
[solder-ball-layer standard](https://wiki.adom.inc/john/adom-solder-ball-layer-standard),
shown in the 3D view above, which also animates the press-fit insertion). The hole must be
plated and fabricated to the drill spec below.

## Dimensions

| Feature | Value | Source |
|---|---|---|
| PCB drill (plated, press-fit) | Ø2.62 mm | dims sheet + footprint |
| Annular ring (copper pad) | Ø4.40 mm | dims sheet + footprint |
| Accepts pin tail | Ø1.85 mm | large pin tail (D5) |
| Head / flange OD | approx Ø4.8 mm | STEP / silkscreen |
| Overall body height | approx 3.9 mm | STEP |

> Press-fit hole sizes are still under validation (Caleb is testing). The Ø2.62 mm drill
> here matches the current dimensions sheet and the shipped footprint; confirm against the
> latest dims sheet before committing a fabrication.

## Files

- **Fusion 360 library:** `MachineContactLarge.lbr` (EAGLE/Fusion, round thru-hole pad + contact symbol)
- KiCad: `MachineContactLarge.kicad_sym`, `MachineContactLarge.kicad_mod`
- STEP: `MachineContactLarge.step`; web 3D: `MachineContactLarge.glb`
- Canonical adom-lbr JSON: `MachineContactLarge.adom-lbr.json`

## Provenance and related

- Original KiCad source: [`adom-inc/adom-kicad-library`](https://github.com/adom-inc/adom-kicad-library) (MachineContact + MachinePin).
- Dimensions: Adom "Machine Pin Dimensions" sheet. Usage and ratings: "White Paper: Molecule Design" (v1.0, September 2025).
- Mating pins: **[adom/machinepinlargeshort](https://wiki.adom.inc/adom/machinepinlargeshort)**, **[adom/machinepinlargestandard](https://wiki.adom.inc/adom/machinepinlargestandard)**.
- Smaller sibling: **[adom/machinecontactmedium](https://wiki.adom.inc/adom/machinecontactmedium)**.