# Assembly and nonprinted parts — Concept 28 R3.1

Use current R3.1 parts together. The main exterior retains the approved shape. These instructions support a first fit assembly, not a released casting batch.

## Hardware — 18 screws

| Use | Quantity | Nominal screw | Head / material |
|---|---:|---|---|
| Shell closure | 4 | M2.5 × 14 mm, 0.45 pitch | ISO 7046 countersunk, metal |
| Front switch clamp | 2 | M2 × 8 mm, 0.4 pitch | ISO 7046 countersunk, metal |
| Speaker keepers | 4 | M2 × 5 mm, 0.4 pitch | ISO 7046 countersunk, metal |
| Microphone keeper | 2 | M2 × 4 mm, 0.4 pitch | ISO 7046 countersunk, metal |
| LED keeper | 2 | M2 × 5 mm, 0.4 pitch | ISO 7046 countersunk, metal |
| Antenna service frames | 4 | M2 × 3 mm, 0.4 pitch | ISO 1580 pan/slotted, **nylon** |

Match head geometry as well as nominal thread size. Countersunk screw nominal length includes its head; pan-head length is measured beneath the head. The blind-floor allowances are small. Confirm actual screws and hole depths on the print and establish tapping/fastening and tightening on a spare before assembly. No heat-set insert pockets or threaded inserts were added for this package.

The two LED screw positions are X=−7 / Y=−3.4 and X=−7 / Y=7.4 mm in assembly coordinates. Historical suffixes on the Fusion screw names do not specify their current locations.

## Other required pieces

- Final PCB release fb5acde7, real SIM7670G module, battery, speaker, microphone breakout and LED specified in the existing build. The supplied populated STEP lacks U6's solid; its CAD replacement is a nominal 24 × 24 × 2.4 mm placeholder.
- Four physical LIDUOLE switches: PTT 6 × 6 × 6 mm; volume up/down 6 × 6 × 5 mm; front 12 × 12 × 4.3 mm. Travel, terminal envelope and force are estimated in this revision.
- Taoglas FXUB63.07.0150C cellular antenna and its cable. GNSS antenna/cable is omitted for this prototype; PCB capability remains.
- Woven metal grille, nominal 45 × 47 mm outline with R10 corners. The visual CAD reference uses 1 mm wire pitch and 0.18 mm wire diameter, approximately 0.36 mm two-wire thickness. Confirm the actual mesh weave, edge treatment, fit and acoustic response. A solid PLA patch would block sound.
- Black acoustic scrim and suitable bond films; use included grille DXFs. Their inherited R1 filenames are intentional, because those outlines were retained in R3.1.
- Measured shims, compliant contacts/keeper pads, battery and PCB cushions, speaker seals, mic offset seal/membrane, LED liners, dielectric antenna seat and rim pads. The complete current list and reference STEP shapes are in `Nonprinted_Fabricated_Parts.md`.

## Default button stack

| Control | Seat shim | Compliant contact | Stop shim | Side backing | Rear pad, installed |
|---|---:|---:|---:|---:|---:|
| PTT | 0.40 | 0.25 | 0.10 | 0.15 | 0.50 |
| Volume up/down | 0.40 | 0.20 | 0.10 | 0.15 | 0.50 |
| Front | 0.40 | 0.25 | 0.10 | — | — |

All values mm, including any adhesive. Each key uses two stop shims. The default is not a measured switch qualification. Seven button DXFs provide reusable cutting profiles. Seat alternatives 0.20/0.30/0.40/0.50 mm and stop alternatives 0.05/0.10/0.15 mm come from changing stock thickness, not printing every variant. Follow `Button_Adjustment_Guide.md`, including starting a gentle bench check with the shorter-stroke 0.15 mm stops and establishing the actual switch's operating point.

## Assembly order

1. Print and clean Plate 01. Trial real switches, their solder/insulation envelope and the holders. Confirm the 0.40 mm lips survived and each nominal switch seats without spreading or cracking the cradle.
2. Print the shell pair and retainers. Remove brim/support, particularly the side-control passages and internal light mount. Check pilot holes, registration pins, mating seams and the rear keeper features. Do not remove functional ribs, pins or the light guide sleeve as if they were support.
3. Fit speaker seals, speaker and its two keepers; fit the microphone's soft offset seal, membrane, breakout pads and relieved keeper. Keep acoustic openings clear. Fit the real clear lens, coupler, LED liners and LED keeper following `Light_Assembly_Notes.md`. PLA L01/L02 are for dry fitting only.
4. Fit the four carriers, real switches, selected seat/contact/stop pieces and front clamp. Use side cradle backing and rear pads. The PTT cradle is at Y=17 mm. Check free return and electrical state at the center and edges of each control before bonding caps.
5. Fit the antenna dielectric seat/stops and two removable service frames with nylon screws. Fit PCB/battery cushions, actual PCB and battery; dress wiring clear of screws, closures and moving controls. Check U6 and connector clearances with the physical hardware.
6. Bring the rear shell into place by hand. Verify that no force or screw tightening is needed to overcome interference. Close evenly using the confirmed fastening method. Recheck all button travel/return with the shell closed.
7. Add cosmetic caps, grille/scrim and the flexible grip/bumper only after fit checks. Allow for the modeled bond thickness. Check sound and actual indicator output; test cellular RF and powered thermal behavior on the assembled prototype.

The original CAD assembly was not resized or redesigned for FDM. Any fit correction beyond cleaning print artifacts should be recorded as a proposed CAD change rather than silently filing away a structural feature.