Every machining supplier can send a quote. The difference between a good partner and an expensive lesson shows up in the quality-control/”>first articles, the inspection records, and what happens when the drawing changes. This article gives a practical process for building a shortlist, scoring candidates on the things that actually predict quality, structuring an RFQ so quotes are comparable, and running a pilot order that tells you whether to continue.
Build the Shortlist Around the Part Type
Start with the part, not the brochure. A shop that excels at aerospace aluminum may be wrong for your brass fittings. Ask what they machine most, what materials they hold in stock, what inspection equipment they run, and for examples of parts structurally similar to yours. “We do CNC” is not an answer.
The Qualification Scorecard
Score shortlisted suppliers on the factors that affect delivered quality:
| Factor | What to verify | Why it matters |
|---|---|---|
| Machining capability | Machine types, axes, materials, tolerance examples | Process must fit geometry |
| Inspection equipment | CMM, calipers, gauging, documented plans | Critical dimensions need real verification |
| Quality system | ISO 9001 or equivalent scope, registrar | Process control and traceability |
| Communication | Response time, DFM feedback, change control | Errors surface in conversation first |
| Reference parts | Comparable projects, first-article samples | Evidence beats claims |
Assign weights by your priorities. If surface finish is critical, weight inspection and finishing experience over machine count.
What to Put in the RFQ Package
A comparable quote needs a comparable spec. Include:
- 3D CAD and a controlled 2D drawing with material grade, dimensions, GD&T, and surface callouts.
- Quantity, development stage, and target lead time.
- Which features are critical (fit, surface, thread, sealing) and how they are inspected.
- Documentation required with delivery.
Ambiguity in the RFQ is a lottery ticket: you will get a price, and you will not know what it bought.
Reading the First Article Report
The first article is the moment of truth. Check that the report measures the features you marked critical, on the equipment agreed, against the tolerance on the drawing. A report that measures only easy dimensions is not a first article report; it is a form.
Compare the measured values to your tolerance band, not to “close enough.” Where a feature drifts, ask what changed in the process, not just for a corrected part.
Quality System Questions That Matter
- Who writes the inspection plan, and does the drawing drive it?
- How are non-conforming parts handled, and is there corrective action?
- How is material traceability maintained?
- How are drawing revisions controlled so the floor always machines the current revision?
Communication and Change Control
The price of a change after quoting depends on control. Ask how the supplier handles a drawing update: do they re-quote, re-inspect, and re-document, or quietly adjust? A supplier whose process absorbs changes without documentation is a supplier who will lose your tolerance history.
Score the Pilot Order
Run a small paid order as a pilot, then score it: on-time delivery, first article against spec, inspection documentation, communication quality, and how issues were handled. Decide before the pilot what scores mean “continue,” “fix,” or “walk away.” Repeat orders are too expensive to discover this later.
When the Audit Fails
If a candidate fails on the factor you weighted most (inspection, communication, or process control), do not buy on price to compensate. A lower quote on a part that does not meet spec is not cheaper. Re-engage only if they can correct the specific gap and demonstrate it on the next sample.
The Bottom Line
Choose a supplier the way you would choose any critical supplier: on evidence, weighted by what your part needs, verified with a pilot order. Structure the RFQ so quotes are comparable, read the first article against the drawing, and score the process not just the price. The right supplier is the one whose documentation survives your inspection – on the first article and the hundredth.
Note: specifics of tolerance, finish, and documentation depend on your part; adapt the scorecard weights to the features that matter most.