The same ten mistakes cross our quoting desk every week. Each one is avoidable, and each one costs the buyer real money — usually invisibly.
We quote hundreds of RFQs a month from North America and Europe, and the same patterns show up again and again. None of them come from careless buyers — they come from smart people working with incomplete information about how a machining floor actually prices and plans work. Here are the ten we see most, with the fix for each.
A STEP file tells us geometry — it doesn't tell us what matters. Without callouts, we have to quote the whole part to the tightest reasonable interpretation, and that price protects us, not you. Ten minutes marking up a drawing (even a PDF over the model) usually moves the quote down a visible notch, because only the features that need precision get priced for precision.
Putting ±0.01 mm on every dimension feels safe and costs you everywhere. Tight tolerances change the process: extra finishing passes, slower feeds, more scrap, more inspection. On a 100-feature part, maybe five features carry real function. Call those out tightly and leave the rest at general profile — your unit price reflects the five, not the hundred.
Tolerance is not a wish, it's a process choice. Standard 3- and 4-axis milling holds around ±0.01 mm; five-axis work ±0.003 mm; turn-mill ±0.0025 mm; precision mold cores and cavities ±0.002 mm. If your drawing asks a 3-axis part for 5-axis precision, either the price jumps or the supplier quietly misses. Match the tolerance to the process and the process to the function.
We regularly return RFQs with a simpler fix: a deeper pocket re-designed for standard tooling, an internal corner re-radius, a datum that makes fixturing sane. Buyers who take the ten-minute DFM call usually save more than they would from a week of price haggling. A supplier who never pushes back on manufacturability is quoting you a problem, not a part.
The cheapest quote often skips line items — no setup breakdown, no finish pricing, no stated inspection plan. The missing money comes back as rework, expedited freight and schedule slip. Ask every bidder to quote the same structure: piece price at quantity, setup, surface treatment, inspection reporting and shipping. Then compare.
"Quality control" means different things on different floors. The questions that matter: Is first-article inspection done on every run? Is final verification on a CMM with a report per shipment? Is material traceable to heat lots? We inspect 100% of first articles and ship Zeiss CONTURA CMM reports with every order — ask any supplier you shortlist to match that, in writing.
Anodizing, plating and painting frequently take longer than the machining itself, especially when outsourced. If your timeline assumes "metal in a box" and the finish adds ten days, the whole chain slips. Ask who does the finishing, in-house or partner, and put its lead time on the Gantt chart next to the machining.
Your part geometry is your IP, especially for components that reveal how your machine works. A supplier worth your order signs an NDA before receiving drawings and restricts project access inside the plant. We sign NDAs as standard practice before files arrive — make that a precondition, not a favor.
One supplier, one production line, one customs event away from a stopped assembly. You don't need dual sourcing from day one, but you do need a supplier who can flex — from one prototype to bridge runs of thousands on the same lines, with the same process discipline. Ask how capacity steps up before you need it.
A wall of machine brand names says nothing about whether your part gets inspected properly or quoted by an engineer. Equipment matters — we run 37 machining and 14 inspection machines, including a dozen five-axis centers and three Zeiss CMMs — but the questions that predict your experience are about people and process: who does DFM, how fast RFQs turn around, what the first-article pass rate looks like over time.
Every mistake on this list gets cheaper the earlier it's caught — ideally before the RFQ leaves your desk. If you want a second pair of eyes on a drawing before you send it out to bid, our engineers will do exactly that, and quote within 4 working hours on standard RFQs.
Send your drawing for a 4-hour quote →
Related: CNC tolerances explained · Getting an accurate quote in 4 hours · Supplier evaluation checklist (free download)
