6061 Aluminum Deep Cavity Housing 5-Axis CNC Machining Mirror Polished Ra 0.05

A Mirror Cavity Is A Machining Problem, Not A Polishing Problem

Buyers ask for a mirror-polished cavity because of what the surface does — optical reflection, vacuum conductance, cleanability, or light distribution inside an instrument. What they actually receive depends on what happened before the polish: if the cavity walls were roughed with a long tool that deflected, no amount of polishing recovers the wall position, and if the floor was cut with a worn insert, polishing smears the tool marks instead of removing them.

So the sequence is fixed. The cavity is roughed with a short, rigid tool path, semi-finished with a controlled step-over that leaves a uniform scallop, and then finished on the same 5-axis setup so the wall, floor and rim share one datum and one workholding condition. Polishing follows as a controlled operation with a defined allowance, not as a cosmetic afterthought. Depth, wall position and rim flatness are measured before and after polishing so you can see what the finishing step actually moved.

Process Route

Precision And Surface Data

Ra 0.05 µm is a measured number, not a description: it is checked with a roughness tester at three positions in the cavity and reported with the part. Where the geometry is too tight for a stylus, we compare against a polished coupon from the same batch and note the method used.

Materials, Finishes And Non-Standard Geometry

• Material: 6061-T6 for optical and vacuum cavities; 7075-T6 where stiffness matters; 304 or 316L stainless for corrosive or high-vacuum bake-out duty; TC4 titanium quoted separately.
• Finish: mirror polish Ra 0.05 µm; satin Ra 0.4; bead blast on external faces only; anodize where the cavity is not optical (anodize is never applied to a polished optical cavity); passivation for stainless.
• Geometry: single or multi-cavity, stepped cavity floor, curved or angled walls, fillet radii from 0.5 mm, seal groove in the rim, lightening pockets outside the cavity, mounting flange.
• Interfaces: O-ring groove, tapped ports, dowel holes, optical window seat, conductive gasket land.
• Size: cavity from 10 mm to 400 mm across, depth-to-width ratio up to 4:1 with a tapered tool strategy.
• Input: STEP, IGES, X_T, DXF, PDF, or a damaged cavity we scan and re-model before machining.

Confidentiality For Precision Geometry

A cavity drawing often reveals the optical or vacuum architecture of a product, not just a shape. We sign a mutual NDA before opening any file — ours in English or Chinese, or your own form — and return a countersigned copy before work starts. Access inside the plant is limited to the project engineer, the 5-axis programmer and the cell supervisor, with the file held in a restricted folder rather than the open shop network. The cell is a camera-free area: no photographs, no video, no social posts, and no customer part displayed or reused as a sample. Subcontracting requires your written approval, and at program close drawings and inspection data are deleted or returned with written confirmation.

The Plant Behind The Cavity

Dongguan Changxinda Precision Technology Co., Ltd has machined custom metal parts since 2008 — 15+ years, 90 to 100 staff, 50–60% of output exported to North America and Europe, 200+ customers served, turnover in the RMB 10–20 million band. The plant runs 4-axis and 5-axis CNC machining centres, turn-mill combined lathes and CNC lathes under an ISO 9001:2015 quality system, serving medical, robotics, automotive, aerospace, automation, laser, LED, lithium battery and precision instrument programs. Billet machining, 5-axis finishing, polishing coordination and final inspection happen in our own plant in Dongguan.

Ten Industries We Machine For

Cavities and precision housings from this plant ship into ten sectors. The list below is what customers actually order, not a marketing wish-list.

All ten sectors run through the same plant and the same ISO 9001:2015 inspection discipline — only the material, finish and documentation package change.

Delivery You Can Plan Around

• Prototype: 3–7 working days after drawing approval; 10–15 days where a deep cavity requires a polishing trial.
• Small batch 10–100 pcs: 7–14 working days.
• Repeat orders: released from the archived program, fixture and polishing recipe — no re-programming, no re-polishing trial.
• Capacity: 10,000 pieces per month across the plant.
• Visibility: a dated progress note with photos of your actual part at roughing, finishing and post-polish inspection.
• Shipping: polished faces filmed, parts bagged, foam-lined export carton or crate, express or air and sea per your forwarder.
• Rush: weekly overtime slots held for urgent prototype and line-down work — give us the deadline and we confirm before the order.

Buyer Questions

Q: Is the mirror polish done by hand or by machine?
A: Both, by geometry. Open floors and gentle walls are polished with an abrasive-flow or felt-bob operation that removes a controlled allowance; tight fillets and corners are finished by hand with diamond paste. Either way the allowance and the target Ra are written on the job traveller, and the result is measured, not judged by eye.

Q: Does polishing move the cavity dimensions?
A: It removes 5–20 µm depending on the process, which is enough to matter at 0.01 mm. We measure the cavity before and after polishing and report the deviation, and where the drawing is tight on wall position we pre-compensate the finish path so the polished wall lands on nominal.

Q: Why not anodize the polished cavity?
A: Anodize is a conversion layer with a matt, slightly scattering surface — it destroys the optical function of a mirror cavity and can craze in a vacuum bake-out. We anodize external faces only, or use chromate where the cavity must stay conductive, and never coat a polished optical surface unless the drawing explicitly asks.

Q: What depth-to-width ratio can you machine without chatter?
A: Up to about 4:1 with a tapered tool and a tilted-axis finish path, and deeper on open geometry. Beyond that we change strategy rather than push a long tool: shorter tool holders, stepped depths, or a two-piece design discussed with you during DFM review.

Q: Minimum order and quotation speed?
A: One piece, no tooling charge. Price follows cavity size, depth, material, tolerance band and finish requirement; a written quotation normally returns within 24 hours of receiving the drawing or model, with a DFM note on any feature that will not cut as modelled.

Q: Do you sign an NDA before receiving drawings?
A: Yes, routinely, and a countersigned copy comes back before work starts. Only the engineer, programmer and supervisor see the file, no photographs leave the cell, and nothing about your part appears in our catalogue or website.

Send The Drawing, Get A Date And A Price

Attach the model or drawing with the quantity and the deadline, and you will get a quotation, a process route including the polishing step, and a firm delivery date. NDA paperwork can be handled in the same exchange.