What is CNC machining? A buyer's primer

What CNC machining is, what it makes, the tolerances to expect, and what drives the price, written for someone about to send a drawing.

Quick answer: CNC machining is subtractive manufacturing. A computer-controlled mill or lathe cuts a part out of solid stock (aluminum, steel, plastic) to tight tolerances, often plus or minus 0.005 in and finer. It is the default for precision metal parts from a single prototype to a few thousand pieces. Cost is driven by cycle time, material and setup, not part count. For most custom precision parts, it is the first process to price.

If you have a drawing and a deadline, this is the process you are probably buying. Here is what actually matters before you send it.

How it works

A machinist (or a CAM program) turns your 3D model into toolpaths, and the machine removes material until the stock becomes your part. Two families cover most work: milling (the tool spins, the part is fixed) makes prismatic parts like housings and brackets; turning (the part spins, the tool is fixed) makes round parts like shafts and fittings. Axis count is how many directions the machine can move at once.

Call out the tolerances that matter, not all of them

Do not send a sketch and ask for "tight tolerances." Tight, to a machinist, is a number and a datum. Holding plus/minus 0.001 in on every dimension can triple your bill for no reason. Call out the three or four features that actually mate or seal, leave the rest at a sensible plus/minus 0.005 in, and your quote drops. The "we run 5-axis" banner in the lobby does not mean your two-plate bracket needs it. 5-axis earns its rate on impellers and contoured parts, not on work a 3-axis mill finished cleanly in 1994.

What drives the cost

Cycle time (how much metal comes off and how many setups), material, and tolerance. Aluminum 6061 cuts fast and cheap; stainless and titanium run slow and cost more. Prototypes cost more per part because setup is not spread over a run. For a live ballpark by complexity and quantity, use the CNC machining cost estimator, and see CNC machining shops across Canada or CNC turning for round parts.

What to send for a quote

A STEP or IGES model plus a drawing that flags the critical tolerances, the material and grade, the quantity (prototype vs production), any finishing, and required certifications like AS9100 for aerospace. Send it once and request quotes from Canadian machine shops, and we match you to shops tooled for your material and tolerance.

FAQ

What does CNC stand for?

Computer Numerical Control. The machine follows a program rather than a hand-cranked operator, which is what makes the parts repeatable and precise.

How accurate is CNC machining?

Standard machining holds around plus/minus 0.005 in without fuss. Turning holds tighter on round features, and grinding or EDM reach into the tenths (0.0005 in and finer). Every tighter tolerance adds cost, so spec them only where the part needs them.

Is CNC machining expensive for one part?

Per part, yes, because setup is not amortised. A simple aluminum bracket might be a few dollars each in production but $80 to $150 as a one-off. For a single functional prototype, that is usually still the right buy.

CNC machining or 3D printing?

Machining for strength, tight tolerance and metal parts. 3D printing for complex geometry, very low volume, or shapes you cannot cut. They are complementary, not rivals.

What materials can be CNC machined?

Aluminum, steel, stainless, titanium, brass, copper and most engineering plastics. Grade matters: name it (6061-T6 vs 7075) so the quote reflects the real material.

Last reviewed: July 2026. Related reading: forging vs casting and MIG vs TIG welding.