Custom Metal Parts Manufacturing: RFQ, Drawing & Supplier Guide

Kernpunten

• An effective RFQ includes 10 elements — CAD files in STEP format, exact material grades, Toleranties per ISO 2768, quantity breaks, annual volume, surface finish specs, required quality documentation, Toepassing context, target lead time, and compliance requirements. Missing any one can add days to your quote cycle.
• ISO 2768-m is sufficient for most industrial parts. Tightening to ISO 2768-f adds 1.5–2× to machining cost; ultra-precision Toleranties (±0.001–0.005 mm) can increase cost by 10–24×. Call out tight Toleranties only on functional surfaces.
• Ontwerp decisions determine 70–80% of manufacturing cost. Materiaal selection, tolerance callouts, and part geometry lock in most of your cost before a supplier ever sees the drawing — a DFM review at the Ontwerpfase is the highest-ROI step in custom part sourcing.
• CNC-bewerking and Plaatwerk crossover at 250–500 pieces. Below that volume, CNC from billet is usually cheaper per part. Above it, plaatmetaalbewerking (cut, bend, weld) becomes more economical due to lower material waste and faster cycle times.
• A structured supplier evaluation saves more than price shopping. ISO 9001 certification, apparatuurlijst, in-house Inspectie capability, and communication responsiveness predict project outcomes better than the lowest quote.

Ordering custom metal parts — whether a one-off prototype bracket or 5,000 Productie enclosures — is fundamentally a communication exercise. The quality, cost, and lead time you get back depend almost entirely on the clarity of what you Verstuur out. Yet most RFQs arrive at a machine shop missing at least one critical piece of information: no material grade, no tolerance standard, a PDF screenshot instead of a STEP file, or a quantity field that says “TBD.” Each missing detail triggers an email thread that adds hours or days to the quoting cycle.

This guide walks through how to specify custom metal parts so your RFQ returns accurate quotes the first time — covering RFQ structure, drawing Voorbereiding, tolerance selection, supplier evaluation, cost drivers, and process selection across CNC-bewerking, plaatwerk fabrication, and Lassen.

How to Write an RFQ That Gets Accurate Quotes

An RFQ (Request for Quotation) is not a purchase order — it is a question you are asking a supplier. The more precise the question, the more actionable the answer. These 10 elements belong in every custom metal parts RFQ:

1. 3D CAD files in STEP (.stp) or IGES (.igs) format. STEP is the universal standard for CNC-bewerking and Plaatwerk. STL files (mesh format) are for 3D printing — they lack the geometric precision needed for machining and will be rejected or require expensive reverse-engineering. See our STL vs STP format guide for the full explanation.
2. 2D drawings (PDF) with critical dimensions and Toleranties. The 3D model defines the nominal geometry; the 2D drawing defines what “good enough” means. Mark critical-to-function dimensions with explicit Toleranties and reference a general tolerance standard (ISO 2768-m or -f) for everything else.
3. Exact material grade. “Aluminium” → 6061-T6, 7075-T6, or 5052-H32? “Roestvrij Staal” → 304, 316, or 17-4PH? The price and lead time can differ by 2–3× between grades. See our aluminum grade guide for help choosing.
4. Quantity and quantity breaks. “100 pieces” is a starting point. Also provide: “and pricing for 500 and 1,000 pieces.” The cost-per-part curve is steepest between 1–100 units; providing breakpoints lets the supplier optimize tooling and setup amortization.
5. Annual volume (even if estimated). A part ordered at 100 pieces per order, four times a year, is fundamentally different from a one-time 100-piece prototype run. Annual volume determines whether the shop invests in dedicated fixturing, which can reduce per-part cost by 20–40%.
6. Surface finish requirements. As-machined? Anodized Type II? Passivated? Powder coated? Each finish adds a separate process step and cost line. Be specific: “bead blast + clear anodize per MIL-A-8625 Type II, Class 1” is actionable; “nice finish” is not.
7. Required quality documentation. Do you need a dimensionaal inspectierapport (FAI per AS9102)? Materiaal certifications (mill test reports)? Certificate of conformance (CoC)? Each document adds Inspectie time — specify only what your quality system actually requires.
8. Toepassing context. A one-sentence description — “this bracket mounts an optical sensor in a 24/7 Productie line with ±5°C temperature swings” — tells the supplier things the drawing cannot: that vibration matters, that thermal expansion matters, and that a failure is expensive. Good shops use this information during DFM review.
9. Target lead time. “ASAP” means different things to different shops. “4 weeks” or “need delivery by August 15” lets the supplier tell you honestly whether they can hit the date — and whether a rush fee applies.
10. Compliance or certification requirements. ISO 9001? AS9100 (aerospace)? ISO 13485 (medical)? ITAR? RoHS/REACH? Not every shop holds every certification — filtering upfront saves everyone time.

Drawing Voorbereiding: What Makes a Manufacturing-Ready Drawing

The 2D drawing is the legal definition of the part. The 3D model shows what the part looks like; the drawing defines what is acceptable. A manufacturing-ready drawing includes:

• Title block: part name, drawing number, revision, material, finish, general tolerance standard (ISO 2768-m or -f), units (mm or inch), scale.
• Orthographic views: at least three views (front, top, right) plus an isometric view. Section views for internal features.
• Critical dimensions with explicit Toleranties: mark the dimensions that affect fit, function, or assembly. Every other dimension falls under the general tolerance standard.
• Datum reference frame: three mutually perpendicular planes (A, B, C) from which all measurements are taken. Without datums, the inspector and machinist may measure from different reference surfaces and reach different conclusions.
• GD&T callouts where needed: flatness, parallelism, perpendicularity, position, and profile Toleranties are the most commonly used symbols for metal parts. A position tolerance of Ø0.2 mm on a hole pattern says more than coordinate dimensions with ±0.1 mm on each axis — the position tolerance creates a cylindrical tolerance zone that is functionally larger.
• Notes section: “Remove all burrs and sharp edges,” “Passivate per ASTM A967,” “Dimensions apply after coating” — these three notes alone prevent the most common receiving-Inspectie rejections.

Tolerance Selection: When ISO 2768-m Is Enough

The single most expensive four characters on a metal part drawing are “±0.05” applied universally. Tolerance selection is a cost lever. Here is the real cost impact of each tolerance tier:

The practical rule: Apply ISO 2768-m as your drawing’s general tolerance. Then add explicit, tighter Toleranties only on the 3–5 features that actually affect fit or function. A drawing with 50 dimensions and three tight callouts costs what it should. The same drawing with 50 tight callouts costs 3–10× more — and most of those tight dimensions are on surfaces that will never mate with anything. See our full tolerance standards guide for more detail.

Supplier Evaluation: Beyond the Lowest Quote

Price comparison is the starting point, not the finish line. A supplier evaluation for custom metal parts should weigh three categories:

Technical & Quality (Weight: ~50%)

• ISO 9001 certification — minimum baseline for any Productie supplier. AS9100 for aerospace, ISO 13485 for medical.
• Apparatuur list with capacities — does the shop have the right machine size, axis count, and tolerance capability for your parts? A shop running 3-axis mills cannot efficiently produce 5-axis geometry.
• In-house Inspectie equipment — CMM, vision system, surface roughness tester, hardness tester. If the shop outsources Inspectie, add time and risk to your supply chain.
• Materiaal certifications — can they provide mill test reports (MTRs) for the specific heat/lot of material used in your parts? Critical for aerospace, medical, and pressure-containing Toepassings.

Communication & Service (Weight: ~30%)

• Quote turnaround time — 24–48 hours is the industry norm for straightforward parts. Longer than 72 hours suggests the shop is overloaded or disorganized.
• DFM feedback quality — did they catch the impossible undercut? Did they suggest a material substitution that saves money? A supplier who asks engineering questions during quoting will save you problems during Productie.
• Engels (or your language) proficiency — if technical discussions require a translator, miscommunication on Toleranties or finishes is a question of when, not if.
• Reference checks — ask for a recent client in your industry. A five-minute call with a previous customer reveals more than any certification.

Cost & Business (Weight: ~20%)

• Payment terms — standard for first orders is 30–50% deposit, balance before shipment. Established relationships may move to Net 30.
• Shipping capability — can they handle export documentation, Incoterms, and your preferred freight forwarder? International shipping logistics are a supplier capability unto themselves.
• Minimum order quantity (MOQ) — some shops will not touch orders under $500. Others specialize in prototype-to-low-volume work. Find the shop whose sweet spot matches your order profile.

What Drives Custom Metal Part Costs

Most buyers focus on the unit price line. The real cost structure of a custom metal part looks like this:

Quantity breaks are real and steep. A prototype bracket that costs $85 each at 10 pieces might cost $22 each at 500 pieces. The setup cost (CAM programming, fixture, first-article Inspectie) is amortized across the entire order. For Productie quantities, always request pricing at 2–3 volume breakpoints — the difference between 100 and 500 pieces can halve the unit cost.

CNC-bewerking vs Plaatwerk vs Lassen: Which Proces for Your Part?

The first decision in custom metal manufacturing is process selection. Verstuur a Plaatwerk part to a CNC-only shop and you will pay for a billet-machined version at 5× the intended cost. Here is a practical decision framework:

The hybrid approach: many Productie parts use Plaatwerk for the main structure (low cost, low waste) with secondary CNC-bewerking on critical features like bearing bores, dowel pin holes, or seal surfaces. This “fabricate then machine” workflow captures the cost advantage of Plaatwerk at volume while maintaining precision where it matters. If you are unsure which process fits your part, include both the 3D model and Toepassing context in your RFQ — a good supplier will propose the optimal process mix during DFM review.

Common RFQ Mistakes That Delay Your Quote

1. Verstuuring a PDF screenshot instead of a CAD file. A screenshot of a 3D model is not a manufacturing file. The supplier cannot extract dimensions, check draft angles, or generate toolpaths from an image. They will reply “please Verstuur STEP file” and your quote clock resets. Always attach the native CAD file — STEP (.stp) is the universal format for metal manufacturing.

2. Leaving the quantity field blank or “TBD.” Quantity determines whether the shop quotes a prototype setup (one-off fixturing, manual programming) or a Productie setup (dedicated fixture, optimized toolpaths, automated Inspectie). Without a quantity, the supplier must guess — and most will quote the higher prototype price to protect themselves. Even a range (“50–200 pieces”) is better than nothing.

3. Applying blanket tight Toleranties. A drawing with “+/-0.05 mm” in the title block on every dimension forces the machinist to treat every feature as critical. Most features on a typical bracket do not need ±0.05 mm — they need ISO 2768-m (±0.2 mm for dimensions under 30 mm). Call out tight Toleranties only where function demands them, and your quote will reflect the difference.

4. No surface finish specification. “I want it to look good” means different things in different shops. As-machined? Bead blasted? Anodized? Each finish is a separate process, often at a separate facility, with its own cost and lead time. Specify the finish on the drawing or in the RFQ body — if you are unsure which finish is appropriate for your Toepassing, ask the supplier for a recommendation during quoting.

5. Choosing the supplier based on price alone. The lowest quote often reflects what was left out, not what was included: no Passivering, no Inspectie report, no material certification, no shipping. Compare quotes line-by-line, not bottom-line to bottom-line. A $50 part with included Inspectie and certification is often cheaper in total cost than a $35 part that arrives non-conforming and needs replacement.

Get Your Custom Metal Parts Quoted Right

The difference between a smooth Aangepaste onderdelen order and three weeks of email threads comes down to the quality of information in your initial RFQ. Verstuur a STEP file, a marked-up drawing with explicit Toleranties, a material grade, and a quantity — and a good supplier will return an accurate quote within 24–48 hours, often with DFM suggestions that save you money. BravoFabs biedt custom metal parts manufacturing across CNC-bewerking, plaatwerk fabrication, and Lassen for industrial clients in Europe and North America. Every RFQ includes a free engineering review — Verstuur us your drawings and we will help you get the specification right before Productie starts.