Key Bent Versus Snapped Versus Worn Cuts Decision Tree

Why this matters

A customer arrives with a key that "doesn't work anymore" and the cause splits across three distinct failure modes that look similar at a glance but require completely different responses. A bent key has shifted geometry that can sometimes be straightened in the shop, and the cylinder is usually fine. A snapped key has fractured and may have left a fragment inside the cylinder, requiring extraction before anything else can happen. A key with worn cuts has lost material from years of insertion and removal, and the duplicate-from-this-key path will reproduce the worn dimensions rather than the original spec. Telling the customer which scenario they are in determines whether the next 10 minutes is a duplicate, an extraction, or a code-cut by impressioning. The branches below resolve which one without a microscope.

Symptom presentation

The complaint usually arrives as "this key worked yesterday and doesn't today" or "I had to wiggle it to make it work and now it won't." Get the key on the counter under good light. Look at it from three angles. Sight along the blade from the tip; a bent key shows a clear deviation from straight. Look at the cut pattern; worn cuts have rounded edges instead of sharp corners, and the depths are visibly inconsistent. Look at the bow for stress fractures; a key approaching snap point usually shows a hairline crack at the shoulder.

If the customer reports the key broke off in the lock, get the fragment if possible. A clean snap at the shoulder usually means torque overload. A snap at the first cut usually means the cut depth was too deep and weakened the blade. A snap at the tip usually means the key got caught at full insertion and was forced.

Ask how old the key is. A key cut 20 years ago that has been used twice daily has seen roughly 14,000 cycles and the cuts are usually noticeably worn. A key cut last month that has stopped working has a different root cause.

Quick checks at the counter

Compare the key to a known-good factory key or to a code-cut reference if the customer has one. A side-by-side comparison shows wear and bending immediately. Lay both keys flat side by side; the bow and the shoulder should line up identically.

Measure cut depths with a calibrated key gauge. Each manufacturer publishes a depth-spacing chart (Schlage SC1 has 10 depths at 0.0150 inch increments; Kwikset KW1 has 7 depths at 0.0230 inch increments). A key with cuts shallow by more than half a depth has lost too much material to operate the cylinder reliably.

Inspect the bow for the customer's key history. A keychain that includes 10+ keys, electronic fobs, and a heavy pocketknife exerts torque on every key it carries; that torque bends keys over time. A key that has lived solo on a single ring tends to last decades longer.

Isolation tree

Branch 1 - bent key, fully intact. Place the key on a flat steel surface and look at the deviation from straight. A bend within 5 degrees over the blade length can be straightened with a brass-jaw vise and careful pressure. A bend greater than 5 degrees has fatigued the brass; straightening will work once and then the key will snap at the bend point under the next torque event. The right call is to cut a fresh key from the original code (if you have it on file) or by impressioning if you do not.

Branch 2 - snapped key, fragment may be in the lock. First, get the fragment out. If the fragment is sticking out of the keyway, use a tip extractor with a small barbed hook (the trade-standard tools are made by HPC and Peterson) or a pair of fine-point needle-nose pliers if there is enough purchase. If the fragment is fully inside, use a snap-on tip extractor designed for the keyway profile. Do not insert a fresh key over the fragment; you will jam the fragment deeper. After extraction, inspect the cylinder for damage and cut a fresh key.

Branch 3 - worn cuts, key insertion is sloppy. The key has lost material below the cylinder's tolerance band. Duplicating from this key reproduces the worn dimensions, so the new key works for a few months and then fails the same way. The correct path is to code-cut from the manufacturer's depth chart, either using the lock's original code from the cylinder (most major brands stamp the code on the bow of the original factory key or on the lock face), or by impressioning a new key against the cylinder.

Branch 4 - key is fine, the cylinder is failed. Test the customer's key against a known-good copy of the same cylinder if possible. If both keys fail in the same cylinder, the cylinder is at fault and the key is a red herring. Pull the cylinder, inspect for worn springs or pins, and rebuild or replace.

Branch 5 - high-security key with restricted blanks (Medeco, Mul-T-Lock, Abloy). Duplicating these keys requires authorization through the manufacturer's restricted-blank program. If the customer is the registered key owner, the duplicate flows through the manufacturer with the appropriate paperwork. If the customer cannot prove ownership of the key system, the duplicate cannot be cut and the conversation becomes one about rekeying the system to issue new credentials.

Confirming diagnosis

The cut-depth measurement is the most diagnostic single test. Each manufacturer's depth-spacing chart is published; a worn key measures shallow relative to spec, a bent key measures correctly but is geometrically off, and a snapped key is missing material. The gauge tells you which.

For lock-side confirmation, the cylinder bench test is direct. Pull the cylinder, take the keyway plug out, and inspect the pin chambers and the driver pins. Worn driver pins or damaged springs explain why a perfectly cut key no longer turns the lock; the key was not the problem.

For high-security cylinders, the depth chart is restricted but the manufacturer-authorized locksmith program provides the chart and the blanks together. If you are not in the program for that system, refer the customer to one who is.

Remediation

For bent keys (Branch 1), straighten only as a last resort and only if the customer understands the key will fail again. The durable fix is a fresh cut by code or impressioning.

References

• ANSI/BHMA A156.5 American National Standard for Cylinders for Door Locks and Latches - the standard governing key, pin, and cylinder dimensions and grades.
• ANSI/BHMA A156.30 American National Standard for High Security Cylinders - the standard for restricted-keyway and key-control systems.
• UL 437 Standard for Key Locks - the security listing referenced for high-security cylinders.
• Manufacturer depth-spacing charts (Schlage, Kwikset, Yale, Medeco, Mul-T-Lock, Abloy) - the cut-depth specifications used in code-cutting and impressioning.
• ALOA (Associated Locksmiths of America) trade reference materials - field references for impressioning and key extraction technique.