TEST FIXTURE · AL 6061 · ANODIZED
380 holes, one flatness callout, and an anodize bath.
Hole position ±0.01 mm and flatness 0.01 mm across a 320 mm plate. The anodize bath is where this part usually goes wrong — after it has been measured.
- Material
- AL 6061-T6
- Size
- 320 × 240 × 12 mm
- Holes
- 380, position ±0.01
- Flatness
- 0.01 mm
- Finish
- Black anodize, bores masked
- Inspection
- CMM + pin gauge
- Typical lead time
- 7–10 working days
- Typical quantity
- 1–50 pcs
Representative program — figures are typical for this part class, not a specific customer record. Machined at a partner shop we manage; we don't own the machines.
THE PROBLEM
Anodizing moved the part by 0.04 mm.
The plate was machined flat and anodized afterwards. The coating built up unevenly, the bores closed by roughly 20 µm, and the plate bowed. Probe pins would not enter, and the fixture no longer sat flat on the table.
- Hole position measured before anodize, never after
- No masking on bores that had a pin fit
- Both faces machined in separate setups, so the datums disagreed
| Flatness | 0.01 mm, both faces |
|---|---|
| Hole position | ±0.01 mm |
| Hole fit | Ø3 H7, pin gauge |
| Coating | Black anodize, 15–20 µm |
| Material | AL 6061-T6, mill cert |
WHAT WE DID
Face both sides first, then drill — and measure at the end.
The sequence matters more than the machine. Facing after drilling pulls the holes out of position; anodizing after measuring hides the error until the customer finds it.
- 1
Two faces, one setup
Both faces faced in the same fixture so flatness and parallelism come from one datum.
- 2
Stress relief
Relief cycle between roughing and finishing on 6061 plate, before any hole is drilled.
- 3
Drill and ream in one program
All 380 holes from the same zero, reamed to H7, no re-chucking between operations.
- 4
Mask the bores
Plugs in every hole before anodizing; coating thickness checked on a coupon from the same bath.
- 5
Verify after coating
Flatness on granite, position on CMM, every hole pin-gauged — on the finished part.
INSPECTION & DOCUMENTATION
Measured after the coating, not before.
Anodize is part of the manufacturing process, not a detail after it. The inspection report reflects the part the customer receives.
- Flatness on granite plate, both faces
- CMM hole position against the drawing datum
- Go/no-go pin gauge on all 380 holes
- Coating thickness certificate from the anodizer
- 6061-T6 mill certificate by heat number
WHAT THIS ROUTE GIVES YOU
Measured after the coating, not before.
This route typically runs 7–10 working days for a batch of twelve. Flatness and hole position are verified on the finished, anodized part — the state the customer actually receives.
- Every hole pin-gauged after anodizing
- Flatness reported on the finished part
- Masking is standard on coated fixture plates
Coating always moves the part. Plan for it.
Send the drawing with the finish callout — we'll quote the masking and the after-coating inspection with it.