Machining Purchase Order Terms That Actually Protect the Buyer

A purchase order is the only document that outlives a project. Drawings get revised, the engineer who approved the sample moves to another team, and the email thread that explained why one bore was opened by 0.05 mm disappears into somebody's archive. When money or a shipment is on the line, both sides read the PO — and if it is thin, the argument is settled by whoever has the better memory.

The exposure is concentrated on machined parts. A bracket may carry 60 dimensions, of which 12 govern fit, and one missed thread note can scrap a 400-piece run. These are the clauses most often missing when RFQs reach our shop in Guangming District.

Put the revision in the header and in the line description

Revision control fails predictably. The buyer issues rev C on Monday, the shop acknowledges on Tuesday, the designer issues rev D on Wednesday because a hole moved 2 mm, and the shop cuts metal on Thursday against the file it already programmed. Three habits prevent it. State the revision letter and drawing date in the PO header, not only in the attachment filename. Repeat the revision inside the line-item description — "BRK-4412, rev C, 2026-09-30, 250 pcs, 6061-T6, clear anodize" — so the traveler carries it. Then require the supplier to echo the revision back on the order acknowledgment with the drawing filename and file size. If the acknowledgment says rev D and the PO says rev C, you found the problem before the saw cuts.

Add one sentence: only the revision named on the PO is authorized, and superseded revisions must be confirmed in writing before material is released. We accept files to 50 MB; anything larger needs a channel agreed in advance.

Define "conforming" before the first chip

Most disputes are not about whether a part is good. They are about which measurement decides. A drawing invoking ±0.01 mm general tolerance and a 0.8 µm finish leaves room for two honest people to disagree at the receiving bench.

Write the acceptance criteria into the PO. Name the drawing revision and the tolerance standard governing dimensions, and list critical characteristics explicitly — typically 8 to 15 callouts out of 60 on a machined bracket. Set sampling: 100% inspection of critical characteristics on the first article and the last piece of each lot, AQL sampling on the balance. Specify the measurement method wherever it is ambiguous: which instrument, at what temperature, clamped or free. A 1.5 mm wall measured in a vise and measured free can differ by 0.03 mm. State what happens to nonconforming parts — return, rework at supplier cost, or use-as-is under a written deviation signed by your engineer.

One dimensional report per lot is normal; a full layout on every lot is not, and asking for it adds 3-6% to the piece price.

See also: Tooling Cost Amortization and Fixture Ownership and CNC Capacity Planning: Reading a Supplier's Promise Date.

The change order process: one page, three signatures

Scope creep in machining is rarely dramatic. It is a chamfer added late, a material swap from 6061 to 6082, a quantity change from 200 to 260. Each looks trivial and each consumes engineering, programming, and sometimes material already cut.

Make the mechanic explicit. Any change — drawing, quantity, date, material, finish, packaging — needs a written request referencing the PO number. The supplier responds within 24 hours with the cost delta, schedule delta, and whether material or work in progress is affected. The buyer approves in writing before work continues; a phone call is not approval. Add a sentence that the supplier may not substitute alloy, finish source, or machine for its own convenience, and that unapproved substitution is grounds for rejection at supplier cost.

Tooling, fixtures, and who owns the programs

If the buyer pays for a fixture, the buyer should own it. A dedicated hydraulic fixture for a family of housings typically runs USD 1,200-4,000 and takes 5-10 days to build. If the relationship ends, you either take delivery of a crate or write the money off.

Reasonable terms: buyer-funded tooling is buyer property, tagged with the PO number and stored at the supplier for the life of the program at no charge. The supplier maintains it and may not run other customers' work on it without permission. On request it ships FOB Shenzhen or DAP at buyer cost in a reusable crate. CAM programs usually remain supplier property even when the fixture is yours; if you need them, negotiate separately and expect to pay. Standard cutters and collets are consumables and stay with the shop.

Warranty, liability cap, and the clauses buyers skip

A workable warranty runs 12 months from delivery or 6 months from end-customer shipment, whichever comes first. It covers dimensional nonconformance and material defects, and excludes wear, misuse, and damage caused downstream in your own assembly.

The liability cap is where the real negotiation happens. A supplier will typically cap total liability at PO value or at the price paid for the nonconforming lot. Push for rework cost plus a defined line-down charge, and expect the price to move by 1-2% for it. Nobody carries uncapped liability on a 20,000-piece order at a 4% margin.

Force majeure should name events rather than gestures: typhoon closures in Guangdong, port congestion, power curtailment, customs holds, epidemic controls. "Acts of God" alone invites argument. Add a 48-hour notice obligation and a duty to mitigate.

Incoterms and payment belong in the same document

Pick one Incoterm and write it with the named place. "FOB Shenzhen, Yantian" is a term; "FOB China" is a conversation. The choice decides who books freight, who clears export, and whose insurance responds to a wet carton in Rotterdam.

Payment follows the same logic. Our default is 30% deposit with the balance before dispatch, moving to net terms only after several clean lots. Put it in the PO, with the currency and which side pays the wire fee. Our how we work page describes the sequence from RFQ to dispatch, and any clause above can be negotiated before you send the first drawing.

Frequently asked questions

Should the PO reference the drawing or physically attach it?

Do both. Reference the drawing number and revision in the line item and attach the PDF to the PO package, because a reference alone breaks when a shared drive gets reorganized. The attachment is the record of what the shop actually received.

Who pays for a fixture built for my part?

The buyer, normally, and therefore the buyer should own it. Expect USD 1,200-4,000 for a dedicated hydraulic fixture on a housing family, with 5-10 days of build time inside the first-article schedule. Get ownership and storage in writing before the fixture is built.

Is a 12-month warranty standard for machined parts?

It is a common starting point: 12 months from delivery, or 6 months from shipment to your end customer, whichever comes first. The scope matters more than the length — dimensional and material defects in, wear and downstream damage out.

How much does an uncapped liability clause cost?

Usually the order. A shop running 4% net margin cannot accept uncapped exposure on 20,000 pieces, so a buyer who insists finds the supplier declines or prices 5-8% higher to self-insure. A cap at PO value plus agreed rework cost is the clause that gets signed.

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