# Concept 27 UC1 - urethane casting review

UC1 is a separate process option. Concept 27 R2 remains available unchanged. The approved exterior, grille pattern, centred microphone, controls and placed OEM hardware are retained.

## File authority and build route

- Finished nominal CAD: cad/Walkie_One_Concept_27_UC1_CASE.step (74 solids), REFERENCE_ASSEMBLY.step (430 solids) and 56 individual part STEP files.
- Casting masters: four separate files under cad/casting_masters. These are master-pattern geometry, not mold halves. The front master deliberately has NO grille holes. Do not assemble or deliver this blank face as a finished part.
- Drill the 121 holes from Grille_Secondary_Drill_Coordinates.csv, in the finished CAD coordinate system: X across the width, Y up, front Z=0. Diameters 1.4 / 1.8 / 2.2 mm; front skin is 2.2 mm through this field. Use a backed-up fixture and establish actual locating datums from a measured first casting. Check burrs, breakthrough and hole positions. The nominal re-drilled master is checked against finished CAD.
- STEP units are millimetres. No global shrink scaling, machining stock, finish offset or tool compensation is applied. RPS must select compensation after resin, master process and cure are agreed.
- Local 1-degree release tapers, with a 0.10 mm straight root land, remove material from the outer walls of 16 existing closure, speaker and antenna bosses. Hole axes, axial seat planes and the exterior envelope stay unchanged. The small loss of annular seat area must be included in load/torque qualification.
- UC1 is not globally drafted. Soft silicone tooling permits some undrafted walls and undercuts; release still depends on split lines, peel direction, resin stiffness and mold tear strength. RPS chooses actual mold construction, gates and vents. Gate/vent geometry is not supplied or approved here.

## Materials and finish

Cast the two rigid shells in an RPS-selected tough ABS-like urethane, and the rim / PTT grip separately in elastomeric urethane. Evaluate Shore A 80-85 for the two soft pieces against hand feel and tear resistance. Cast urethane is not PA12, TPU or injection-molded PC-ABS. The 10 internal rigid carriers remain PA12 prototype parts. The two optical parts, three aluminium caps, stock and adhesives retain separate fabrication routes.

Original and Palladium use identical UC1 geometry. The metallic Palladium shell is a finish proposal on urethane, not solid palladium or a metal-shell CAD variant. Select coating with RF/electrical compatibility review. Physical chips and coated samples establish acceptance; the proposed Pantone matches do not authorize an exact colour claim.

## Limits that matter before a run

Review all thin features, especially the inherited 0.8 mm rear battery divider and approximately 0.75 mm microphone cradle wall. Confirm fill and release, or revise these regions with RPS; UC1 does not certify a minimum wall thickness. Do not remove or thicken these features blindly into electronics / battery keepouts.

Existing M2 and M2.5 pilot interfaces are retained. Urethane thread strength and repeated-service life have not been established. No metal threaded inserts are modeled; do not press or heat arbitrary inserts into the current small bosses. If inserts are required, first agree the insert specification, boss redesign, clearances and assembly validation.

Follow Assembly_Sequence.md, then First_Article_Inspection.csv. Physical resin properties, cure distortion, tolerances, soft-pad loads, actuation, harness, acoustics, optics, RF and drop durability are open. This is a supplier-review package, not a tooling or fabrication release.

## Source and verification

This revision is a local editable BRep derivative of the preserved Adam-derived R2 geometry. Adam authentication was unavailable for this revision; UC1 was not generated or approved by a new Adam task. Inputs are SHA-256 locked. Source imports STEP geometry only; it does not execute attached files. Rebuild using Python 3.12 with build123d 0.11.0, cadquery-ocp 7.9.3.1 and trimesh. Run source/build_Concept_27_UC1.py.

Checks cover valid STEP exports, part counts, watertight part meshes, unchanged nominal bounds, subtractive-only device edits and re-drilling of the blank front master. Removing boss-side material cannot introduce a new rigid overlap; this construction argument is not a fresh complete motion/force/tolerance audit. Coincident-face boolean differences in the inherited rear shell can be unstable, so volume deltas and subtractive construction are identified explicitly in the audit. Baseline assembly logic remains R2 and requires physical qualification for the new materials.

## Process references

- RPS urethane casting: https://www.rapid-products.com/service/urethane-castings/
- Fictiv Urethane Casting Design Guide, August 2024: https://www.fictiv.com/wp-content/uploads/2024/08/urethane-casting-design-guide.pdf (wall / feature guidance pp. 13-17; draft / undercuts pp. 21-22; inserts p. 25; drawing communication p. 37). These are general guidelines, not RPS acceptance criteria.