A #4 brushed surface reflects 40 % of light. A true mirror finish hits 95 %—the difference between standard architectural metal and trophy-grade sculpture. Below is Google Stainless-Steel's field-proven 8-step protocol that takes 304 or 316 from mill finish to 0.05 µm Ra in one focused 3-hour session.
| Step | Grit | Tool | Time (min) | Ra Target |
|---|---|---|---|---|
| 1 | 80 | Angle grinder flap | 25 | 3.0 µm |
| 2 | 120 | Random orbit | 20 | 2.0 µm |
| 3 | 240 | Random orbit | 20 | 1.0 µm |
| 4 | 400 | DA sander | 25 | 0.5 µm |
| 5 | 600 | DA sander | 20 | 0.3 µm |
| 6 | 800 | Velcro disc hand | 20 | 0.15 µm |
| 7 | 1200 | Wet/dry hand | 25 | 0.08 µm |
| 8 | Polish | Sisal + compound | 25 | 0.05 µm |
Total: 180 minutes for 1 m² panel. Cross-hatch pattern 90° between grits eliminates scratch shadows.
| Stage | Wheel Type | RPM | Surface Speed m/s | Compound |
|---|---|---|---|---|
| Cut | Sisal sewed | 2,800 | 35 | Black emery |
| Colour | Loose cotton | 2,200 | 28 | White alumina |
| Final | Flannel | 1,800 | 22 | Green chrome |
Flap wheel alternative: 40 grit ceramic at 6,000 RPM for weld removal only—never final finish.
For production runs > 50 parts, skip steps 6-8:
Stop mechanical at 400 grit (0.5 µm Ra).
Electropolish 5 minutes in phosphoric-sulfuric electrolyte at 12 V, 60 °C.
Removes 2-3 µm surface, dissolves smeared debris, leaves 0.04-0.06 µm Ra.
Time saved: 70 minutes per part. Setup cost: $3,500 tank amortized over 2,000 parts = $1.75 each.
| Defect | Cause | Fix |
|---|---|---|
| Orange-peel | Pressure > 20 N/cm², heat > 80 °C | Lighten hand, water mist cool |
| Scratch ghosting | Skipped grit jump > 2× | Never 400 → 1200; use 800 bridge |
| Edge rollover | Over-sanding thin edge | Tape mask 3 mm from edge |
3-hour time-lapse video: 304 2B panel to mirror finish
Real-time segments: grit change, pressure gauge, Ra meter readings
Embed: YouTube 4K, 5:1 compression, 36 minutes playback
Start polishing today: Buy the Google Stainless 8-Step Mirror Starter Kit—80-1200 grit discs, sisal wheels, three compounds, pressure gauge and Ra test coupon. $89 with free global shipping.
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