A five-step buyer's guide — from defining the part on a drawing to approving the order and shipping the lot.
Getting a custom part CNC machined is a five-step process: define the part, find a qualified shop, request a quote, review the quote, and approve the order. The mechanics are not complicated — the discipline is in doing each step thoroughly enough that the part you receive is the part you specified. This guide walks each step, calls out what an experienced buyer does at each stage, and points to deeper resources. If you're already past Step 3 and ready to send a package, jump to request a quote.
Every quotable part starts with five facts on a drawing: geometry, material, tolerance, finish, and quantity. The first three are non-negotiable inputs; the last two are inputs that drive price and lead time more than buyers expect.
The best package is a dimensioned 2D drawing in PDF plus a 3D model in STEP format. The PDF carries the dimensions, tolerances, datum references, and notes that the shop quotes against. The STEP file makes programming faster and removes ambiguity from contoured features. If you only have a CAD model, export a STEP file and an annotated PDF before sending the RFQ.
Specify material by alloy and condition: not "aluminum," but "6061-T6" or "7075-T651." Not "stainless," but "303," "304," "316," or "17-4 PH H1025." If you are open to alternates, say so — sometimes a near-equivalent alloy is in stock and a specified one has an eight-week lead time. The materials hub lists what we work routinely.
Tolerance is the single biggest price driver after geometry. Default-block tolerances of plus/minus .005 inch are inexpensive. Plus/minus .001 inch is mid-range. Plus/minus .0002 inch — our tight-tolerance routine — requires careful fixturing, often a separate inspection step, and sometimes a second machine. Tighten only what needs to be tight; the rest of the print should run on default tolerances. See CNC tolerances explained for what each class actually means in practice.
Tell the shop how many you need now, and the expected annual usage (EAU) if there is one. A prototype quote on five pieces with an EAU of 500 looks different from a flat prototype quote — the shop will recommend fixturing decisions that pay off in production.
"Qualified" means three things: capability fit, quality system, and contracting fit.
Does the shop's equipment match your part? A 1.25 inch diameter precision turned part wants Swiss CNC machining. A contoured aluminum housing wants 5-axis machining. A bracket with simple prismatic geometry is CNC milling. The capabilities page lays out our equipment list, envelope, and spindle speeds.
For any part that matters, the shop should be operating under a documented quality management system. ISO 9001:2015 is the baseline international standard. For aerospace and defense, AS9100 layers on top. For medical devices, ISO 13485. If you are buying a non-critical commercial part, ISO 9001 is often enough. If you are buying for a regulated program, ask what is certified versus what is "in process."
If you are a government prime or a federal buyer, the shop also needs to be set up to take the contract. Look for active SAM.gov registration, a UEI, a CAGE code, and any required socioeconomic registrations. Our government contracting section covers what to look for.
Send a complete package, all at once. The minimum: a dimensioned PDF drawing, a STEP model, the material specification, the quantity, and the required delivery date. Stronger packages also include: applicable specs (military, aerospace, medical), inspection-level requirements (FAI, source inspection, C of C), finish callouts (Ra in microinches), and any packaging or shipping requirements. The full RFQ checklist is in our guide on how to request a CNC quote.
Send the package to the shop's quoting contact — for us, that is support@quickbrownfox.co. A complete package goes faster than a fragmented one; expect acknowledgement within a business day and a quote within two to three.
A complete quote from a serious shop tells you more than price. Read it for: unit price at each quantity break, non-recurring engineering (NRE) and any tooling or fixturing cost, lead time from PO receipt, tolerance class quoted (and any exceptions taken to the print), finish and inspection level included, and payment and shipping terms.
A quote that takes exceptions is usually a good quote. If the shop says "Note 4 specifies plus/minus .0005 inch on a .500-inch bore; we quoted plus/minus .001 inch as standard. Confirm if tighter is required," the shop has actually read the drawing. Resolve every exception before approving.
Confirm what gets inspected and how the results are documented. For our precision machining work, every part ships against a documented inspection record under the production network's ISO 9001:2015 program; FAI is performed where the contract specifies it.
Approval is a PO, an emailed authorization, or a contract release. The shop confirms the lead-time clock starts at PO receipt (or, for material-constrained alloys, at material delivery). Programming and fixturing run in parallel with material; first-article inspection happens on the first piece; the rest of the lot follows. C of C and any inspection records ship with the parts. If you specified source inspection or a hold point, the shop coordinates that with you before shipping.
After delivery, the part exists as a quoted, approved, inspected, traceable record in the shop's quality system. The next order on the same part number runs faster because the program is built, the fixturing exists, and the inspection plan is documented — which is why repeat work is almost always less expensive than the first run.
A dimensioned 2D drawing in PDF is the minimum — it carries the tolerances, datum scheme, and finish callouts that the machine shop quotes against. A STEP or other neutral 3D model is strongly recommended on top of the PDF; it speeds programming, eliminates ambiguity on contoured features, and usually shortens lead time.
A complete RFQ package is typically acknowledged within one business day and quoted within two to three business days for standard scopes. Tight-tolerance or specialty-alloy work may take longer if material sourcing is required.
A first-article inspection (FAI) is a documented dimensional verification of the first piece produced against the drawing. For aerospace, defense, and medical work, FAI is typically required by the contract. For commercial prototype work it is optional but recommended on any part with tight tolerance or GD&T.
Yes — CNC shops have built parts from 2D drawings for decades. Expect a small programming-time uplift versus quoting against a model, and expect the shop to ask clarifying questions on any contoured features that are easier to convey in 3D.
Cost depends on material, tolerance class, geometry, quantity, and required inspection. The single biggest cost driver for low-volume custom CNC work is programming and setup time amortized over the run quantity; doubling quantity often does not double cost. The fastest way to get a real number is to send a drawing.
If the same shop can do both, yes. The prototype run de-risks tolerances, fixturing, and inspection plan. Carrying that knowledge into production saves the production shop from re-learning the part — and saves you from re-paying for first-article work. Our prototype and production services run under the same QMS.
The full RFQ checklist and what a good quote should contain back.
What each tolerance class costs and when to specify which.
When to choose subtractive over additive for your part.
The full custom-parts service line, one-off through production.
Part families we build routinely.
Skip ahead and send the package.
