0.008mm Roundness Bearing Seat Pocket Housing in 7075-T6 Aluminum with Masked Hard Coat for CNC Drone Bearing Housing

Hard anodizing grows about 25 µm per surface, and on a Ø20 H7 seat that is 0.05 mm of interference nobody budgeted for. This CNC machining parts housing finishes the seat at 0.008 mm roundness and 0.01 mm squareness, then applies 50 µm of hard coat to the wear faces only — the pocket is masked, so the bearing still goes in with the fit the drawing asked for.

Hard anodizing is not paint. It converts the surface and grows roughly half inward and half outward, so 50 µm of coating takes about 25 µm off the bore radius — 0.05 mm on diameter. A housing that met H7 before coating becomes an interference fit after it, and the assembly press damages both the coating and the bearing.

The fix is not to open the bore before coating and hope. It is to mask the seat, coat the wear faces that actually need abrasion resistance, and hold the seat at 0.008 mm roundness with a 0.01 mm squareness shoulder so the bearing sits flat. Coating thickness is measured on every part, and the seat is re-gauged after coating.

• Masked fits — 50 µm of hard coat on wear faces, none in the seat or on the shoulder.
• Roundness 0.008 mm — measured after coating, not before.
• Square shoulder — 0.01 mm, so the bearing race is not tilted by the retaining land.
• Groove in the right place — grease groove at mid-seat, edge broken so the bearing is not shaved on entry.

1. Fit and coating review — bearing part number, fit class, coating thickness and masking zones agreed before machining.
2. Material verification — 7075-T6 received by heat number, ultrasonic checked, 3.1 certificate retained.
3. Rough machining — block, seat bore and seal land roughed with 0.6 mm allowance, symmetric removal.
4. First stress relief — low-temperature relief so the seat does not close in after boring.
5. Semi-finish — seat bore and shoulder semi-finished with light radial engagement.
6. Second stress relief — a second cycle before finishing keeps the seat round through its depth.
7. Finish boring — seat bored to H7 Ø20 at 0.008 mm roundness, shoulder faced square to 0.01 mm, grease groove cut in the same clamping.
8. Hard anodizing — 50 µm on wear faces, seat and shoulder masked, thickness measured per part.
9. Verification — seat re-gauged after coating, CMM on roundness and squareness, seal land flatness, FAI shipped.

Seat size, wall thickness, sealing arrangement and coating spec follow the shaft and the environment, so the housing is built per assembly. Send the bearing and seal drawing and we return a DFM note on masking zones, coating thickness, shoulder design and grease groove placement within 24 hours.

• Seats — single or twin bearings, with preload shoulder or wave washer pocket.
• Coating — 25 to 60 µm hard coat, or chromate conversion where conductivity matters.
• Sealing — O-ring land, lip seal bore, or a labyrinth groove for dusty environments.
• Lubrication — grease groove, oil port, or a sealed-for-life bearing pocket.
• Sampling — 1 pc pressed with your bearing and gauged after coating.

Motor geometry, stator stack and winding data are competitive information, so access is limited from the drawing stage onward.

• NDA first — mutual NDA and non-circumvention signed before any file is exchanged.
• Isolated area — dedicated machines and authorized staff, no phones or photography inside.
• Codified routing — internal codes on travelers and labels instead of your part numbers.
• Data control — per-project folders on a permission server, destroyed on request with a record.
• No display — no drawings, part photos or logos in samples, catalogs, the website or social media.

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Two shifts 07:30–22:00, six days a week, with weekend shifts in peak season. Capacity is locked weekly for volume programs, so a rush order never displaces a scheduled batch.

• Samples — 7–10 days, checked on your stator or bearing set before the batch is released.
• Batch — 15–20 days from deposit and drawing approval.
• Buffer stock — semi-finished stock for repeat models, cutting repeat lead time by about 30%.
• Shipping — DHL/FedEx/UPS in 3–5 days for samples; air or sea for volume; EXW Dongguan, FOB Shenzhen or CIF.
• Documents — FAI, 3.1 material certificate, CMM report and packing list with every shipment.