Key Cutting: Code Machines, Duplicators, and Bitting Specifications

Key Cutting: Code Machines, Duplicators, and Bitting Specifications

Why Precision Matters

A key that is cut even slightly out of specification may fail to operate a lock, damage the cylinder, or — in a master-key system — open locks it should not. Every cut you make must fall within the manufacturer's published tolerance, typically ±0.005 inch. That small margin leaves no room for guesswork, which is why locksmiths use calibrated machines, key micrometers, and published bitting specifications rather than relying on feel alone.

Reading a Bitting Specification Chart

A bitting specification chart (also called a depth and space specification chart) lists everything you need to cut a key for a given keyway family:

• Depths — the set of allowable cut depths, numbered from shallowest (usually #1) to deepest (usually #9 or #10 depending on the manufacturer). Each depth has a precise measurement in inches from the bottom of the cut to a reference surface.
• Spacing — the distance from the bow stop (shoulder) to each cut position, and from cut to cut.
• MACS (Maximum Adjacent Cut Specification) — the largest allowable difference in depth between any two neighboring cuts. Exceed the MACS and the key may bind or the cuts may undercut each other, creating a weak spot or allowing unintended shear-line alignment. For example, a MACS of 4 means cuts numbered 1 and 5 may be adjacent, but cuts 1 and 6 may not.
• Blank designation — the Ilco, Silca, or JMA blank number that matches the keyway.

Always verify the keyway before selecting a blank. A blank that fits the cylinder face but belongs to the wrong keyway family will produce a key that cannot reach the correct shear line.

Code Machines (Semi-Automatic)

A semi-automatic code machine such as the Framon DC-100 or Ilco 045 positions the key blank at precise depth and spacing settings dialed in by the operator. The machine does not interpret a code on its own — you read the bitting list, enter each depth value by setting a depth stop or numeric dial, and then clamp and cut.

Setup steps:

1. Select and install the correct cutter and spacer for the keyway family.

2. Calibrate the machine. Most code machines have a calibration key and test-cut procedure described in the manufacturer's manual. Perform calibration at the start of every work session.

3. Load the bitting specification for the key code you are cutting.

4. Set the depth stop to the first cut value; set the spacing stop to cut position 1.

5. Clamp the blank firmly so it cannot shift during the cut.

6. Make the cut, advance to position 2, reset the depth stop, and continue.

7. After all cuts are complete, deburr the key with a file or buffer wheel before testing.

Manual Duplicators

A manual duplicator (pantograph-style) traces an original key and reproduces its profile on a blank. The tracer stylus follows each cut valley while the cutter reproduces the same motion on the new blank.

Key points for accurate duplication:

• Clamp alignment — both the original and the blank must be clamped at exactly the same shoulder reference point. A misaligned blank shifts every cut.
• Worn originals — a key worn through use will have shallower, rounded valleys. The duplicate will copy those errors. Always compare a duplicate to the original with a micrometer and bitting gauge. If the original is out of spec, cut to code instead.
• Cutter sharpness — a dull cutter causes dragging that rounds the bottom of cuts and raises the effective depth measurement. Inspect cutters regularly and replace as needed.

Measuring with a Key Micrometer

A key micrometer reads the depth of each cut from the reference surface of the key shoulder. To measure:

1. Place the anvil of the micrometer against the shoulder reference surface.

2. Lower the spindle to the bottom of the cut.

3. Read the measurement and compare it to the published depth value for that cut number.

A tolerance of ±0.005 inch means a published depth of 0.300 inch is acceptable anywhere from 0.295 to 0.305 inch. Record every measurement on your tolerance worksheet before moving to the next key.

Safety and Shop Practices

• Eye protection — metal chips and cutter fragments can become projectiles. Wear safety glasses rated for impact protection whenever a cutter is spinning.
• Hand position — keep fingers clear of the rotating cutter. Use the machine's clamp; never hold the blank freehand.
• Deburring — always deburr cut keys before inserting them into a cylinder. A sharp burr can scratch a pin chamber or score a plug, creating locksmith liability.
• Machine guarding — never remove or bypass the cutter guard on a code machine or duplicator.
• Housekeeping — metal shavings accumulate quickly. Sweep or vacuum the work area regularly; fine swarf is a slip and cut hazard.
• Calibration log — record every calibration check. If a machine is found out of calibration, re-cut all keys produced since the last verified calibration.

Putting It Together: From Code Book to Cylinder

A complete code-cutting workflow runs: look up the key code in the Ilco or Silca code book → identify the keyway and blank → read the bitting list → verify MACS compliance → calibrate and set up the machine → cut → measure every cut with a micrometer → deburr → test in a practice cylinder. If a cut is out of tolerance, you must re-cut a fresh blank; attempting to deepen a cut that is too shallow on the same blank often results in an overcut.

Building speed through this workflow — the timed drill targets eight minutes per key — comes from organizing your tools before you start, not from rushing the cuts themselves. Accuracy first; speed follows practice.