Alloy and temper appear in three places, not one State 6063-T5 on the PO, the drawing title block and the packing list. Require an EN 10204 type 3.1 mill test certificate per heat number.

Name the tolerance standard and its edition “Per EN 755-9” is not enough. Write the edition year, and flag the dimensions that govern hardware fit as critical.

Split mill lengths from cut-to-size Different processes, different tolerances, different scrap owner. One line item for both is how you pay for the saw kerf.

Document die ownership before you pay for the die A tooling agreement with an IP clause, a die register entry and a handover condition. Without it, changing supplier means paying twice.

Turn surface finish into numbers Film thickness class, sealing quality, colour difference limit and a retained physical sample. “Anodised” on its own is a wish.

Write the packing specification Bundle weight limit, interleaving, corner protection, no metal banding on visible faces. Damage in transit is a packing failure, not bad luck.

Match the Incoterm to who can actually control the risk FOB plus supervised loading, or CIF with an agreed carrier. All-risks cover, not minimum ICC(C).

Inspect before shipment, not after arrival An AQL sampling inspection at the factory with a written plan. Rejecting a container at your own dock is the most expensive place to discover a problem.

Keep a documented concession route Decide in advance what happens when goods are marginal: accept with a credit, rework, or return. Improvised decisions cost more than the defect.

The trap

The PO says “6063 aluminium profile”. The drawing title block says “AL”. Nobody wrote the temper. The factory extrudes 6063-T5 because that is the highest-yield option on their press, and T5 has roughly 30% less yield strength than T6. Your frame passes assembly, then fails a static load test eighteen months later, or cracks at a bolted joint that was designed around T6 allowables.

The fix

Write alloy and temper as one string — 6063-T5, 6061-T6, 6005A-T6 — in three places: the PO line item, the drawing title block, and the packing list. Then require an EN 10204 type 3.1 mill test certificate per heat number, showing chemical composition and mechanical properties. If a supplier cannot or will not issue 3.1, that tells you something about their mill traceability before you find out the hard way.

The trap

You attach a drawing with nominal dimensions and no tolerance class. The factory applies its default, which for architectural work is often GB/T 5237 — a standard written for window and curtain-wall profiles, where a millimetre of variation is invisible. T-slot hardware is not so forgiving. A slot that is 0.3 mm wide means every T-nut in the assembly is loose, and you find out when the frame will not clamp square.

The fix

Reference a dimensional standard with its edition year, for example “dimensional tolerances per EN 755-9:2016, class normal unless noted”. Then separately list the critical dimensions that govern hardware fit — slot width, slot depth, core hole, wall thickness at the slot — and give them their own tighter limit, typically ±0.10 mm. Marking them on the drawing is not enough; put them in a table on the PO so there is no argument about which drawing revision applied.

The trap

You order “2,000 kg of 40×40, cut to 1,250 mm”. The factory extrudes 6 m bars, cuts on a saw with a ±1 mm stop, and bills you for the full weight. You have paid for the offcut, the saw kerf and the cutting labour, and you have no idea what the yield was. Worse, when the lengths arrive at 1,249.2 mm and your jig needs 1,250 mm, the argument is about whether the drawing said anything about cut tolerance.

The fix

Split the order into mill lengths (supply condition, no cutting) and cut-to-size (a machining operation with its own tolerance). For cut-to-size, specify the length tolerance explicitly (typically ±0.5 mm for a stop-cut, ±0.2 mm for a machined end), require deburring of both ends, and ask for the cut plan with the quoted yield percentage. A factory that can tell you its yield rate is a factory that tracks its scrap.

The trap

The tooling fee appears on the proforma invoice, you pay it, and the die goes into the factory’s rack. Eighteen months later the price creeps up, quality drifts, and you want to move. You discover the die is not yours in any document you can enforce, the drawing is theirs, and a new die costs the same again — plus a fresh trial run and re-approval cycle.

The fix

Before paying a tooling fee, sign a short tooling agreement that states: the die and its design remain your property; the die is identified by a register number physically stamped on it; you may inspect it and take photographs on request; and on termination it will be made available for collection or transfer. Add the commercial side too: how many tonnes the die is expected to run before refurbishment, who pays for maintenance, and the tonnage milestone at which the tooling fee is credited back. Many established plants will amortise or refund tooling once volume passes a threshold — but only if you ask.

The trap

“Anodised” and “powder coated” are not specifications. An anodised layer can be 5 microns or 25 microns; it can be sealed properly or not at all; and “silver” can mean four visibly different colours from four different batches. Importers discover this when the second container does not match the first, by which time the customer has already seen the first.

The fix

Convert the finish into numbers. For anodising: film thickness class per ISO 7599 (AA10 for indoor, AA15 for general exterior, AA20–AA25 for harsh or coastal exposure), a sealing quality requirement, and a colour difference limit expressed as ΔE. For powder coating: powder type, nominal film thickness in microns, adhesion test method, and a colour reference. In both cases, retain a signed physical sample — one with you, one with the factory — and write into the PO that the sample governs in any dispute. A retained sample settles more arguments than any instrument.

The trap

Your drawing has six drilled holes, two tapped M8 threads and a milled counterbore. You assume the extruder will do them. They subcontract the machining to a workshop they do not control, using a fixture they built from your PDF, with no first-article approval and no defined datum. The holes are in the right place relative to each other but the whole pattern is rotated 0.5° against the extrusion.

The fix

List the secondary operations explicitly and mark each as in-house or subcontracted. For anything machined, require a first article inspection report before mass production, name the datum used for location, and give positional tolerance rather than a dimension chain. If a critical feature will be subcontracted, ask to audit that subcontractor or at least see their inspection capability. Extruders are extrusion specialists; machining accuracy is a separate competence.

The trap

Profiles are long, heavy and have a soft anodised surface. Wrap them in thin stretch film, strap them with steel banding at high tension, stack them six high in a 40 ft container, and you will open the doors on bent ends and long friction scratches where the bundles have been breathing against each other for four weeks at sea. Freight damage of this kind is almost never covered cleanly by insurance, because it is classed as inadequate packing.

The fix

Write a packing specification into the PO. The elements that matter most: each profile interleaved or sleeved so anodised faces never touch; corner protectors on bundle ends; a maximum bundle weight that a forklift can handle without flexing the stack; wooden crates or steel-framed pallets rather than cardboard; and an explicit prohibition on metal banding bearing directly on visible surfaces. Ask for loading photographs before the container is sealed — they cost nothing and they change behaviour.

The trap

FOB sounds like the buyer taking control, but if nobody supervises loading and the container is stuffed badly, the damage happens at origin and you own it. CIF sounds convenient, but the seller chooses the cheapest carrier and the minimum insurance cover, and again you own the consequences. Either way, the invoice says the risk transferred at a point where you had no presence.

The fix

Choose the Incoterm by capability, not by habit. If you have no origin presence, FOB with a third-party loading inspection is usually the best compromise: the inspection report is your evidence if the loading was bad. If you do take CIF, name the carrier or at least the shipping line, and confirm the insurance is all risks rather than the minimum ICC(C) that covers total loss only. Read the insurance clause on the invoice before you pay the deposit; changing it afterwards is usually impossible.

The trap

Rejecting a container at your own dock is the worst possible outcome. The goods are in your yard, the duty is paid, the supplier has been paid in full, and your line is stopped. You now have three bad options: accept and absorb the cost, negotiate a credit from a position of weakness, or return the goods and pay freight twice. None of them recovers the schedule.

The fix

Move the decision point to the factory. Commission an AQL pre-shipment inspection with a written sampling plan, and make the final balance payment conditional on a passed report. The plan below is a reasonable starting point for industrial profiles. Crucially, also agree in advance what happens to marginal goods — a documented concession or deviation route with a defined credit formula removes the improvisation that turns a small defect into a large argument.

Send us your drawing and we will tell you what is missing

We extrude, machine and finish aluminium profiles in-house. Send a drawing or a sample and we will come back with the tolerances, finish classes and packing specification we would hold — before you place an order.