One-Off CNC Machining

What counts as a one-off

A one-off is a single part that will probably never be ordered again: the replacement for the one component that took a machine down, a replacement bracket for a test rig, a fixture for a job that runs once, a non-standard fitting for an installation that is already built, the piece that went to engineering review on an instant-quote platform (source 1). It has no production run behind it and no revision B ahead of it. That is what separates it from its two neighbors on this site: CNC parts with no minimum order is the ordering policy (no minimum quantity, no minimum charge), and prototype CNC machining is the iterate-and-scale path for a design that will be revised and then run, while this page is about the single part itself. A team revising a design between one-offs can add prototyping support.

The practical difference is that a one-off is quoted as a finished part, not as the first of a series. No later order shares the programming and setup, so the one piece carries all of it, and a person reads the print first to flag the callouts that would add work without helping the part.

What to send for a single part

A first order moves fastest when the files answer what the quote would otherwise have to ask. The quote form takes any file type, and a STEP model plus a PDF drawing is ideal. The table is the whole checklist. ASME describes Y14.5 as the standard for stating and interpreting GD&T on engineering drawings and models (source 3), so the tolerance and callout items belong on the drawing in that form.

No model yet is a normal starting point. A dimensioned sketch, photos with a scale reference or a new sample part can start the quote, and the CAD work to draw it up is quoted as its own line. A fully dimensioned 2D PDF is quoted without a CAD line.

Why setup is spread over one piece

Every CNC job carries work that does not depend on how many parts follow: programming, fixturing the material and setting up the machine. Wikipedia’s article on design for manufacturability says the cost of CNC machining is driven by time, including the set-up time of the machine, NC programming and fixturing, and that the number of parts plays a critical role in amortizing that set-up and programming time into the cost of each part (source 4). On a run of fifty, each part carries a small share. On a single piece, the one part carries all of it.

That is why the price per part is higher on a single piece than on a run, and why a spare made on the same order shares a setup that is already done (source 4). Two things on the print also move the number. The same article says each operation, meaning each flip of the part, has its own set-up time, and that the tighter the tolerance, the more expensive the component is to machine (source 4). A part that can be cut in fewer operations, with tolerances only where the function needs them, is the easier one to quote. The free design review that comes with every quote looks for exactly those callouts. What determines CNC machining cost goes through the rest of the drivers.

Quoted to the print: the numbers on a one-off

Tolerance follows the print, not the quantity. The bands a single part is quoted to are the same ones a run gets: typically ±0.005 in as the general machined tolerance, ±0.001 in on critical turned diameters, down to ±0.0002 in on a wire-EDM profile, and quoted to ±0.0001 in on a ground diameter, with milled features quoted from the print. Call the critical dimensions out on the drawing and leave the rest at a general tolerance: the loosest tolerance that serves the function, set feature by feature (source 4). CNC machining tolerances covers how to choose the band.

Material is specified by grade, exactly as it would be for a run: 6061 or 7075 aluminum, 303 or 304, 316 or 17-4 PH stainless, 1018 or 4140 steel, A2 or D2 tool steel, grade 5 titanium, Delrin or PEEK. A grade or stock size that is not commonly carried can add time, and the quote gives the real date.

From request to inspected part

1. Send what you have through the quote form, using the checklist above; how to order CNC parts covers the ordering steps in full. A sketch, photos or a new sample part is enough to start, and any file type is accepted.

2. A person reads the print before any number exists, flags anything that would add work without helping the part, and asks about anything ambiguous rather than guessing.

3. The quote comes back in 24-48 hours with the price for each quantity you asked for, the material and the lead time for the tier you picked. A special finish is quoted as its own line, and a standard finish sits inside the part price. Shipping is quoted as its own line, or ships on your carrier account.

4. Approve the quote to place the order. Card by secure link (a processing fee applies), ACH, wire or check. The delivery tier you chose sets the date: Rush 1-2 weeks, Standard 4-6 weeks (typical), or Extended 6-8 weeks, for jobs that aren’t time-sensitive. The operations on the print decide which tier a part can use, and how long CNC parts take goes through each one.

5. Before it ships, the part is inspected against your print, and it goes out with tracking. If a part doesn’t match the print, it’s remade or credited.

Choosing a supplier for a one-off part

If the one part becomes a low-volume run, up to 10,000 pieces, the same person quotes it: see small-batch CNC machining, or set MI CNC Parts up as an ongoing CNC machining parts supplier.

The large instant-quote platforms do quote a single piece. Xometry’s published FAQ says it handles everything from one-offs to high-volume production (source 1), and Protolabs’ FAQ states quantities as low as one part for CNC machining (source 2). Both quote from a 3D model: Xometry’s FAQ says its instant quoting engine prices parts from the 3D geometry of uploaded CAD files (source 1), and Protolabs’ FAQ says the way to a quote is to upload a 3D CAD model for an interactive quote (source 2). On Xometry, when a material is not listed, the buyer selects “Other” and submits the quote for expert engineering review (source 1).

Here a person reads the print before any number exists, so the one-off that needs a ground diameter, a tool steel or a sketch turned into a model is quoted the same way as an easy one, with the extra steps named. If speed is the whole question, Protolabs’ FAQ says CNC machining can put parts in hand in as fast as 1 day, and low quantities within 1 to 3 business days (source 2), which is faster than the Rush 1-2 weeks here, so a part that fits an instant-quote platform’s rules may suit you better on speed. If you are holding a competing number for the same part, send it with the files.

One-off hard parts: titanium, tool steel and ground details

Some one-off requests carry a second process. A single grade 5 titanium piece for a test article. One replacement A2 punch profiled by wire EDM to drop into an existing die (punches). One pin with a ground diameter to replace a worn locating pin (shafts and pins). One replacement shaft turned to the bearing fit on the print, for a machine that has been out of production for a decade. One go/no-go gauge for a feature no catalog set covers. One bushing in bronze for a machine whose builder is gone.

Where a part needs a second step, the quote names every step and gives one ship date. If the part has no drawing because the supplier vanished, reverse engineering turns a new sample part into a measured print first, and the one-off is remade to that. Parts are supplied as replacements by fit and dimensions. No OEM logos, part numbers or markings are copied.

Sources

All accessed 4 October 2026. Where a figure here differs from your print, the print governs.

1. Xometry, "Answers to the Most Frequently Asked Questions About Xometry", xometry.com/resources/blog/answers-to-most-frequently-asked-questions/, published 3 November 2025, updated 26 August 2026 (one-offs to high-volume production; when a material is not listed, “Other” goes to expert engineering review; instant quoting prices parts from the 3D geometry of uploaded CAD files).

2. Protolabs, "Digital Manufacturing FAQs", protolabs.com/resources/faqs/, no date shown (CNC machining quantities as low as one part; one to 200 pieces within 1 to 3 business days; parts in hand in as fast as 1 day; an interactive quote from an uploaded 3D CAD model).

3. ASME, "Y14.5 Dimensioning and Tolerancing" (Y14.5-2018, R2024): asme.org/codes-standards/find-codes-standards/y14-5-dimensioning-tolerancing (the standard establishes symbols, rules, definitions, requirements, defaults and recommended practices for stating and interpreting GD&T and related requirements on drawings, models and related documents).

4. Wikipedia, "Design for manufacturability", section "Computer numerical control machining", text available under CC BY-SA, last edited 11 September 2026: en.wikipedia.org/wiki/Design_for_manufacturability (cost driven by time including set-up time, NC programming and fixturing; set-up time per operation; tolerance and cost; the loosest tolerance that serves the function; volume amortizing set-up).