Qualifying a precision machining vendor

Ask which operations are performed in-house and which are coordinated through partners. Both are legitimate — almost every precision supplier coordinates heat treatment and specialist coatings — but you need to know where the boundary sits.

The answer matters because coordinated operations affect lead time, traceability and who is accountable when a part comes back wrong. A supplier who is vague about this is either disorganised or hoping you will not ask.

This is the single most informative question in a qualification visit. A supplier who claims to do everything either has not understood your requirement or is willing to learn on your part.

A clear answer — sizes beyond their envelope, tolerances beyond their process, materials they do not handle, work they decline — indicates someone who knows their own capability. That is what you want carrying your critical parts.

• What equipment do they have, and is it calibrated and traceable?
• Who performs inspection, and is it independent of the person who made the part?
• What is measured at first-off versus in-process versus final?
• What inspection documentation can you receive, and in what format?
• How are non-conforming parts segregated, and who decides on concessions?

Ask not what capacity they have, but what proportion is committed and to whom. A supplier running at full capacity for a single dominant customer is a different risk from one with spread and headroom.

Also worth asking: what happens to your job when their largest customer has an emergency? The answer tells you where you will sit in the queue.

• How do they tell you about a problem — and how quickly?
• Have they ever told a customer about an error the customer had not noticed?
• What does their corrective action look like in practice, not on paper?
• Who is your point of contact when the usual one is unavailable?

For anything proprietary, ask where files are stored, who has access, and whether an NDA can be signed before detailed drawings are shared. A supplier should be able to describe this without having to invent it.

Ask too whether they publish customer names or work, and on what basis. A supplier who names customers freely will name you just as freely.

A questionnaire records what a supplier says. A visit shows how the shop is kept, whether inspection equipment looks used, whether work in progress is identified, and whether the people doing the work can describe it.

Ask to see a job like yours in progress rather than a showcase part. The difference between the two is itself informative.