When a component passes through machining, heat treatment, grinding and coating at four separate suppliers, each is responsible for its own step and nobody is responsible for the finished part. The failures happen in the gaps — allowances, handling, sequence — and they are the hardest to resolve because everyone's own work was correct.
7 min read · Last reviewed 28 September 2026 · All resources
Each supplier in a multi-process route typically does its own operation correctly. What falls between them is the interface: how much material the machinist left for grinding, how the part was protected in transit, what the treatment did to size and form, whether the coating thickness was allowed for.
These are exactly the questions no single supplier owns, and they are where multi-supplier routes fail.
The most common dispute is grinding allowance. The machinist left what they considered normal; the treatment moved the part more than expected; the grinder cannot clean up without going undersize. Each acted reasonably.
The fix is that allowance is a route decision, agreed before machining starts, by someone who understands the whole sequence and its history for that material.
Coordination is not free: the coordinating supplier carries the risk of the whole route and prices it. You may also pay a margin on operations you could buy directly.
Against that, weigh your own time managing four relationships, the cost of a disputed failure, and what a scrapped part represents by the time it reaches the last operation — which is when multi-process parts usually fail.
In a coordinated route, someone should measure the part against the drawing after the last operation. In a self-managed route, this is often nobody's job — each supplier checked its own step and the final result is assumed.
That assumption is where parts reach assembly out of tolerance despite every operation being signed off.
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No, and few do. It means one party plans the route, manages the specialists, and is accountable for the finished part. Ask which operations are in-house and which are coordinated.
The coordinating supplier, toward you — which is the point of the arrangement. How they recover from their subcontractor is their business, not yours.
Usually yes, though it does split responsibility for material condition. Agree explicitly who owns a problem traced to the material.
Include your own coordination time, transport between suppliers, and the expected cost of a failure late in the route. Those are the terms in which the difference shows up.
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