Guides / Sourcing / Choosing a Supplier

How Finished Audio Parts Get Damaged Between the Shop and You

July 6, 2026

A part can be machined correctly, finished beautifully and inspected carefully, and still arrive scratched. On cosmetic work, packing is not logistics. It is the last manufacturing operation.

How the damage actually happens

Not usually in transit. Usually in the shop, in the last hour.

Face to face stacking. Two anodized panels stacked with nothing between them rub against each other with every bump. Black anodize on black anodize polishes to a visible shine.
Bulk bins between operations. Parts thrown into a tote after finishing while waiting for packing.
Bare hands after finishing. Fingerprints on freshly anodized aluminum are usually cleanable. On brass and on some seals they etch.
Tape directly on the finish. Someone tapes a bag shut and the tape touches the part.
Loose parts in a big box. Void fill settles in transit, the parts migrate and end up against the box wall.
Mixed part numbers in one bag. Two different parts rubbing against each other for three weeks in a container.

The packing spec

Write this once, reuse it on every cosmetic part, and reference it on the drawing and the PO.

Level 1. Individual protection.

Every part individually bagged, or wrapped in foam or acid free tissue
Protective film on Zone A faces, applied after finishing
No tape in contact with any part surface
VCI paper for any bare brass, copper or steel

Level 2. Separation.

No face to face contact between parts, ever
Interleave with foam sheet, corrugated board or moulded tray
One part number per bag or per tray compartment
Parts oriented the same way in the tray, so nobody has to rotate one against another to get it out

Level 3. The carton.

Rigid carton, not a bag
Foam or moulded insert that holds the stack, so nothing moves when the box is shaken
Fill any void so the contents cannot shift
Part number, revision, quantity, batch and date on the outside label
“FRAGILE, COSMETIC PARTS, DO NOT STACK” where it applies

Level 4. The pallet, for volume.

Cartons of one part number per layer
Do not exceed the carton’s stacking rating
Edge protectors and strapping that does not bear on carton faces

Trays pay for themselves

For a part you will order repeatedly, a moulded or die cut tray is the single best investment in the packing chain.

A thermoformed tray for a run of a few hundred is inexpensive
A die cut foam insert is cheaper still and works well for flat parts
The tray holds the part in one orientation, keeps faces apart and gives the assembler something to work from at your end
It removes the batch to batch variation that comes from whoever happens to be packing that day

Supply the trays to the shop, or specify them and let the shop buy them. Either way, get the tray designed once and keep it with the fixtures.

Protective film, correctly

Film is the standard answer for flat anodized faces and it has its own rules.

Apply after finishing only. Film adhesive on a pre-anodize surface leaves residue that can show through the finish.
Low tack. High tack film left on for months in a warm warehouse is difficult to remove and can leave adhesive behind.
State a removal window on the label, typically within six months.
Do not film a textured or blasted surface unless you have tested it. Adhesive gets into the texture.
Leave a tab so the film can be lifted without a fingernail on the part.

The purchase order clauses

Short, specific and enforceable:

PACKING REQUIREMENT, APPLIES TO ALL COSMETIC PARTS

1. EACH PART INDIVIDUALLY BAGGED. NO PART TO CONTACT ANOTHER PART.
2. PROTECTIVE FILM ON ZONE A FACES, LOW TACK, APPLIED AFTER
   FINISHING. REMOVAL WINDOW 6 MONTHS, STATE DATE ON LABEL.
3. GLOVES TO BE WORN FROM THE FINISHING OPERATION ONWARDS.
4. NO TAPE IN CONTACT WITH ANY PART SURFACE.
5. PARTS SUPPLIED IN TRAY 9012. TRAYS TO BE HELD BY SUPPLIER
   AND REUSED.
6. CARTON LABEL TO STATE PART NUMBER, REVISION, QUANTITY,
   BATCH AND FINISH DATE.
7. PHOTOGRAPH OF PACKED CARTON TO BE SENT BEFORE DISPATCH
   ON THE FIRST SHIPMENT OF EACH BATCH.

PARTS ARRIVING WITH HANDLING DAMAGE ATTRIBUTABLE TO PACKING
WILL BE RETURNED AT SUPPLIER COST.

Clause 7 is the quiet one that changes behaviour. A shop that knows it has to photograph the carton packs it properly.

Receiving inspection

When the box arrives:

Photograph the carton before opening it. If there is transit damage you have evidence.
Open one bag and inspect before unpacking everything.
Check the label against the PO: part number, revision, quantity, batch.
If you find damage, stop and photograph it in the packing, not after you have handled the part.
Leave the protective film on until assembly. Parts sitting in your own stores get marked too.

That last point is worth repeating. Plenty of parts that arrived perfect are damaged in the customer’s own warehouse in the weeks before they are used. The packing spec applies at your end as well.

Frequently asked questions

Is protective film always a good idea?

On an anodized flat face, yes. On bare aluminum before anodizing, no, because the adhesive can leave residue that shows after finishing. Apply film after the finish, never before, and specify a low tack film with a stated removal window so it does not bake on in a hot container.

Can I ask the shop to ship in my own packaging?

Yes, and for a repeat part it is worth doing. Supply the trays or the specification, and have the shop keep a stock. It costs a little and removes the most common source of variation between batches.

Who pays when parts arrive marked?

Whoever the purchase order says. If packing is not specified, the argument is unwinnable, and most shops will reasonably say the parts left in good condition. Put the packing requirement in writing and the responsibility becomes clear.

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Keep reading

This guide is part of Sourcing and Quality Control for Audio Parts, one of four sections in the guide library.