Integrated top-down controller upper.
Design evidence issued 6 October; installed checks recorded through 12 October. U02 replaces the difficult U01 upper while retaining the existing B01 body and electronics. The later physical results are controlled in the project Test Plan.
1. Why the design changed
User feedback recorded that U01 was positioned correctly, but support removal was difficult. The inner surfaces were rough, and small features broke near the four fan screw or nut locations and the outlet ribs.
U02 removes the inclined side passage. The lid, hood, fan pads and grille now form one connected solid. The fan sits horizontally above the A4988 reference region, with intended intake through the top grille and downward airflow.
The failure mechanism was not instrumented or formally inspected. The redesign responds to the observed manufacturing difficulty; it does not prove improved strength, airflow or cooling.
2. Selected configuration
| Item | Selected design or boundary |
|---|---|
| Printed upper | One U02 part integrates the lid, hood, fan frame and grille. |
| Retained hardware | B01 body, PCB supports and clamps, electronics, and the SUNON fan. |
| Fasteners | Three M3×20 lid screws and four M3×20 fan screws, with standard nuts and washers for the fan. |
| Preserved access | Controls, LED and power openings, Nano and USB access, and existing body wiring access. |
| Reference clearance | The fan lower face is nominally 13.5 mm above the A4988 reference top. This is not a measurement of the installed hardware or wiring. |
3. Digital and slice evidence
The native project reload, triangle identity, non-mirrored transform and MK4S build-volume checks passed at their digital scope.
The estimated part polymer is 75.16 g. The selected orientation trades fewer assembly interfaces for extensive support material and a higher replacement cost. No printer-GUI confirmation is claimed.
4. Air-path calculation boundary
| Geometric section | Area | Interpretation |
|---|---|---|
| Top grille clear opening | 645.13 mm² | Mesh section only; fan blades, hub and physical wires are excluded. |
| Front outlets | 912.00 mm² | Two 24 × 19 mm windows. |
| Rear opening | 918.00 mm² | Parallel exit and wiring opening. |
| Nano-side opening | 610.39 mm² | Parallel exit and service opening. |
The new grille area is 12.18% below the historical U01 grille value of 734.62 mm². A shorter path does not prove greater flow.
Bulk-air energy balance: P_to_air = ρ cₚ Q_useful ΔT_air
Installed flow requires the actual fan curve and system resistance. Geometric access and clear area do not establish a cooling result.
5. Later physical verification status
- U02, the cover and fan are recorded as installed and functioning.
- Enclosure, screw and wiring fit, fan direction, unobstructed cooling paths, and moving- and wet-zone clearances are recorded as checked.
- Separate ten-minute unloaded and bucket runs, a clean-water cycle, and a ten-minute 500-cycle water-loaded run with the lid closed are recorded without reported problems.
- Component-limit evidence, unrestricted thermal duty and final acceptance remain separate from these scoped results.
No source, no fact. No trace, no decision. No test, no pass. This 6 October digital package does not establish the later physical outcomes by itself. The current Test Plan and dated evidence carry those results; no unrestricted thermal rating or final acceptance is inferred.
6. Current physical evidence
12 October: installed enclosure and 500-cycle water-loaded result. Fan on, enclosure closed, bucket and water, no specimens. No abnormal behaviour was reported.
Nano: 26.1 → 24.8°C. A4988: 26.1 → 25.7°C. These measured observations do not establish an unrestricted duty rating.
Three buttons are active. The existing knobs remain installed for handover but are inactive in firmware. The 13.5 mm clearance and fastener specification above are CAD references, not a newly verified installed BOM.
Fabrication files remain in the controlled team package. Current machine configuration and dated physical results are maintained on the machine page.