CNC Machining Cost

Tolerance: the same part, two different prices

Take one part and draw it twice: once with a general tolerance of plus or minus 0.005" and once with plus or minus 0.0005" on the same features. Those are two different prices, because the tighter the tolerance, the more the part costs to machine (source 1). Tight enough, and a feature is better ground or cut by wire EDM than milled (sources 5 and 6), which is a different process with its own price.

None of that is a reason to avoid tight tolerances where a part needs them. It is a reason to put them only where they do a job: the bore that takes a bearing, the face that seals, the pair of holes that locate. Everything else can carry the general note. Machining tolerances covers where that line sits, and the free design review that comes with every quote flags a callout that is tighter than the part needs.

Quantity: one piece carries the whole setup

Setup is the time from the last part of the previous run to the first good piece of yours, and it happens once per run, whether the order is one part or a hundred (source 2). Divide that fixed cost by the quantity and the share each piece carries falls as the run grows (source 3). On a very small lot, setup can take far longer than running the parts; on a large one it may be only a small part of the run (source 2). That is arithmetic, not a discount.

Ask for more than one quantity, such as 1, 25 and 100, and the quote shows each. Small-batch machining goes deeper on how the breaks work, and one piece is still a normal order here: there is no minimum.

Material and stock size

Material shows up in the price in two places: the stock, and how the grade cuts. Aluminum is a much softer metal than steel, stainless steels have poor machinability next to carbon steel because they are tougher, gummier and work harden quickly, and titanium alloys rate low on tool life (source 4). As materials get harder, denser and stronger, they take much longer to machine (source 1). Picking a grade no tougher than the part needs is one of the easiest ways to shorten the cutting time, and choosing a material walks through how. Other alloys and plastics quoted on request. Name the grade on the print.

Stock size matters too. Machining removes material, and the time to remove it is a major factor in the cost (source 1). The free design review with every quote says where a small change would leave less to remove.

Geometry and the number of setups

The shape decides how many times the part has to be fixtured and how long each setup runs. Every extra operation, each flip of the part, adds setup and load time (source 1). A part cut from one or two sides in a single setup avoids that; the same part with features on five faces does not. Features that need smaller tools cost more to machine, and a tight internal corner needs a smaller tool (source 1).

This is why a smaller part can cost more than a larger one. A plain plate the size of your hand, with a bolt pattern and a general tolerance, is a quick job. A smaller part with features on every face, a tight bore and tight internal corners can take longer to make and quote above it. Size is not the price; the work is. Design choices that raise a quote lists the common ones and the cheaper equivalents.

Finish and secondary operations

Anything the print asks for after the metal is cut is a separate step: anodizing, powder coating or passivation, or another finish the print calls out. A finish called out on the print is quoted with the part. A special finish is quoted as its own line, and a standard finish sits inside the part price. A part that needs two steps waits for both. Surface finishes explains what each one does and when a clean as-machined part is enough.

Inspection requirements

Every part is inspected against your print before it ships, and that is already in the price. What changes the number is how much the print asks to be proved: a drawing with a few critical dimensions asks for less checking than one where every feature carries a tight callout. Call out what actually has to be verified, and the quote answers it before you order. No C of C or material certifications ship with parts by default. If your PO needs them, say so before the quote. Inspection reports on critical dimensions aren't included by default. If you need one, ask when you place the order.

Lead time

A rush date moves the price, because the window for buying material, scheduling the work and finishing it is short. Lead time is quoted in three tiers. Rush: 1-2 weeks. Standard: 4-6 weeks (typical). Extended: 6-8 weeks, for jobs that aren't time-sensitive. Rush 1-2 weeks applies to machined parts with no secondary operations. Heat treat, grinding, EDM and finishing add time, and the quote gives the real date. Lead time starts at order approval. Put your need date in the part description and the quote answers it.

How long custom machined parts take explains where the time goes, and rush CNC parts covers what a rush buys and what cannot be hurried.

What this means for your quote

Loosen every tolerance that is not doing a job. Order the quantity you will actually use, spares included, and ask for a second quantity on the same quote. Pick the grade the part needs and no tougher. Keep features on as few faces as the part allows, and give internal corners room. Skip finishes that are cosmetic on a part nobody sees. Call out only the inspection the part needs. Give a real date. And send a STEP model with a PDF print so nothing is guessed. The quote comes back in 24-48 hours from a person who read the drawing, with a note on what is driving the number and where a callout is tighter than the part needs.

Everything above is why a price without a print is a guess. The only accurate price is a quote on your print.

Sources

All accessed 30 September 2026. Where a figure here differs from your print, the print governs.

1. Wikipedia, "Design for manufacturability", last edited 11 September 2026: en.wikipedia.org/wiki/Design_for_manufacturability (tighter tolerance and machining cost; each flip of the part adds setup and load time; harder materials take longer to machine).

2. Mike Lynch, "The Effect of Lot Size on Productivity", Modern Machine Shop, 21 December 2017, mmsonline.com/articles/the-effect-of-lot-size-on-productivity (what setup is and that it comes once per production run; its share on small and large lots).

3. Wikipedia, "Average fixed cost", last edited 29 July 2026: en.wikipedia.org/wiki/Average_fixed_cost (fixed cost divided by quantity; it falls as output rises).

4. Wikipedia, "Machinability", last edited 26 September 2026: en.wikipedia.org/wiki/Machinability (aluminum softer than steel; stainless steels tougher, gummier and quick to work harden; titanium alloys low by the tool-life method).

5. Wikipedia, "Grinding (abrasive cutting)", last edited 27 August 2026: en.wikipedia.org/wiki/Grinding_(abrasive_cutting) (very accurate dimensions; suited to very hard materials).

6. Wikipedia, "Electrical discharge machining", last edited 29 May 2026: en.wikipedia.org/wiki/Electrical_discharge_machining (very hard materials, difficult by conventional machining, cut precisely and to very close tolerances).