CNC Key Cutter Guide: How a Programmed Tool Cuts a Key

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  How a CNC key cutter actually removes metal
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  Which tolerances decide whether a key works
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  Brass, nickel silver, and steel: what each does to the cut
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  Where CNC key cutting stops making sense
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  Mechanical duplicator vs CNC key cutter

A mechanical duplicator copies a key by dragging a stylus along the original. The stylus, the follower spring, and the operator's hand all add error. On a worn original, that error gets copied straight into the new key. A CNC key cutter breaks that chain.

The programmed tool never touches the old key. Instead, the bitting code or a scanned point cloud defines the target geometry, and the machine drives a rotating cutter along that path. Depths are set by the controller, not by how hard the operator pushes. That is the core difference: reference data replaces physical copying.

Cutting action matters too. A 2.5–4 mm end mill or a profile cutter spins at 1200–8000 rpm depending on material and cutter diameter. Brass keys cut clean at higher speeds, while nickel silver and steel blanks need lower feed per tooth to avoid work hardening at the tip.

The machine controls three or four axes. X and Y position the cut in the key plane, Z sets depth, and a rotary A axis handles side-milled profiles on high-security keys. Once the path is proven, every blank in the batch follows the same coordinates.

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  Reference sourceBitting code, scanned profile, or CAD model — not the original key
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  Depth controlServo-driven Z axis, repeatable to ±0.005 mm
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  Typical spindle1200–8000 rpm, 2.5–4 mm cutter
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  Axes3-axis for standard profiles, 4-axis for side milling

A key is a mechanical interface. It has to slide into a cylinder, lift pins to the shear line, and turn without binding. The critical dimensions are cut depth, cut width, and the angle of the ramp between depths. Get any of them wrong by a few hundredths and the key drags or fails.

On a standard pin tumbler cylinder, depth tolerance of ±0.05 mm is usually enough. High-security profiles with tight warding and side pins push that to ±0.02 mm or better. We hold ±0.005 mm on the machines, which leaves margin for plating and for wear in the lock itself.

Surface finish affects insertion feel. A rough cut edge catches on the warding. A light deburr pass with a fine cutter or a nylon brush brings the cut to Ra 1.6–3.2 μm, which is smooth enough for repeated use without removing the depth geometry.

Cut width has its own limit. If the cutter is wider than the pin chamber slot, the key will not enter. If it is too narrow, the pin tips ride on the edge and wear faster. Match cutter diameter to the keyway specification, not to whatever is already in the spindle.

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  Standard cylinders±0.05 mm depth is generally sufficient
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  High-security profiles±0.02 mm or tighter on depth and side cuts
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  Edge finishRa 1.6–3.2 μm after deburr
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  Cut widthMatch the keyway slot; wider keys will not enter

Most keys are brass. It machines fast, holds a clean edge, and costs little. The trade-off is wear. A brass key in daily use will lose its sharp ramp edges over time, and that is exactly why a worn original makes a poor master for duplication.

Nickel silver is harder and more wear-resistant. It cuts with more tool pressure, so feed rates drop and the cutter wears faster. For a batch of keys that must survive years of use, the extra cost is usually justified. Stainless and tool steel blanks appear in industrial and padlock applications; they need lower speeds and often a coolant or mist.

Coating and plating change the final dimension. A nickel-plated key can grow 5–15 μm on each surface. If the cut was made at nominal depth, the plated key may bind. Either cut slightly shallow and let the plating bring it to size, or cut after plating and accept bare edges at the cut.

We machine key blanks and lock components in aluminium 6061, 7075, brass C36000, and stainless 303 and 316L, depending on the mechanism. Material choice follows the lock, not the other way around.

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  BrassFast cutting, low wear resistance, low cost
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  Nickel silverHarder, better wear life, slower feeds
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  Steel blanksLower speed, coolant or mist, higher tool wear
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  Plating growth5–15 μm per surface; plan the cut depth around it

A CNC key cutter is a production tool, not a universal answer. For a single spare key on a common profile, a mechanical duplicator in a locksmith shop is faster and cheaper. Setup time on a CNC only pays back when the geometry is complex or the quantity is above a handful.

The second limit is the original. If the only master is worn, bent, or a poor copy, scanning it will reproduce the error. A CNC can cut accurately from bad data as easily as from good data. Get a code, a factory spec, or a known-good key before you program the path.

Third, the machine needs a clear profile definition. Keys with internal milling, moving elements, or magnetic inserts may not be cuttable on a standard 3-axis setup. Those need a different process or a dedicated machine.

Finally, consider the batch size. Below about 20 pieces, the programming and fixture time can dominate. Above a few hundred, the consistency advantage is clear: every key in the run is identical, which is what a building manager or fleet operator actually needs.

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  Low volumeOne-off spares are usually cheaper on a duplicator
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  Bad masterA worn original produces an accurately wrong key
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  Complex profilesInternal milling or inserts may need a different process
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  Batch sizeCNC pays off above roughly 20 identical pieces