When a Copied Key Works Only Some of the Time, Read the Pattern

A copied key that works only sometimes is usually a marginal match. Its cuts come close enough to the lock's pins to turn on a lucky try, but not on each try, so the problem is fit rather than a random fault. The original key is the quickest first clue: if the original turns smoothly in the same lock and the copy doesn't, the copy is the likely problem.

Why a copy turns on one try and misses the next

Inside a common pin tumbler lock, small spring-loaded pins sit in a row across the cylinder. Each cut on the key lifts one pin stack to a set height. When every stack stops with its gap at the shear line, the seam between the turning core (the plug) and the fixed housing, the plug can rotate.

A copy with a cut slightly too deep or too shallow leaves a pin just off that seam. Locks have a little internal play, so a wiggle or extra twist sometimes nudges the pin into line. That is the hit-and-miss result.

What to notice at the door before changing anything

Use the keys normally, with no tools and no more force than an ordinary turn, and pay attention to what happens.

• Does the original key turn this lock smoothly on each try?
• Does the copy work in the other locks it was made for?
• Does the copy need jiggling, a slight pull back out, or pressure up or down before it turns?
• Does it fail in one direction only, locking but not unlocking or the reverse?
• Does it turn easily with the door held open and struggle once the door is shut?
• Is it getting harder over days or weeks, or was it always like this?

Notes kept over several days tell you more than one frustrated attempt.

What each pattern most likely means

Only the copy misbehaves

When the original is smooth, the copy's cuts are probably off. The copy may have been made from another copy, so small errors stacked up, or from a worn original whose rounded cuts were reproduced. If easing the key back out slightly makes it turn, the cuts may sit a little out of step with the pins.

Both keys misbehave

When the original also misses, the lock is the more likely source. Worn pins or grit inside the cylinder blur the fit for any key, so a copy that used to work can start missing because the lock changed.

It changes with the door

If the key turns freely with the door open but drags once the door is shut, the bolt is probably rubbing on the strike, the metal plate in the frame. The key is carrying that load, so it feels like a key fault when it isn't.

Never right, or going downhill

A copy that was awkward from day one points at how it was cut. One that worked well and then declined points at wear, and the original key's behavior tells you whether that wear is in the key or the lock.

These are likely readings, not verdicts. An off copy and a worn lock can turn up together, and each makes the other show sooner.

Why forcing it or copying the copy backfires

Extra twist stresses the narrow neck where the blade meets the head of the key. A key bent there can crack, and one that snaps inside the cylinder turns a nuisance into a lockout. Hard jiggling also wears the pin tips and the peaks of the key's cuts, widening the mismatch that started the trouble.

A new copy made from the bad copy repeats its error and adds whatever small error the next cut brings. The cleanest starting point is the least-used original you have.

Picking the next step

If only the copy misbehaves, have a fresh copy cut from the original and try both in the same lock. If the new one turns smoothly, retire the old copy so it doesn't drift back onto someone's key ring.

When the original also misses, the lock feels gritty or rough, or the result changes with the door, stop forcing the key and have the lock inspected. Depending on what's worn, the answer might be a rekey, which resets the pins to work with a new key, or a lock change when the cylinder itself is worn. A result that tracks the door usually calls for door or strike work rather than a new key.

For that inspection, call NoMad Locksmith & Security at (917) 337-9703. Non-emergency lock work is by appointment. If the key fails and you're locked out, the 24/7 emergency lockout service handles that.

Frequently asked questions

Can a brand-new copied key already be worn out?

A brand-new copied key can carry wear it never saw. Copying traces the shape of the source key, so if that source has rounded, shallow cuts from years of use, the new key reproduces them in fresh metal. It looks new and fits like an old key. Starting from the least-worn original avoids passing that wear along.

Is it safe to keep using a key that only works with jiggling?

A key that only turns with jiggling is a stopgap. Light use buys a little time, but the margin shrinks as the key and pins wear. Stop using it once it needs real force, shows a bend near the head, or catches partway through the turn, because a key that snaps in the cylinder leaves you locked out.

Does rekeying a lock fix a key that works intermittently?

Rekeying can clear up an intermittent key when the cause is worn pins or a set of poor copies, since the pins are reset to a new key and the old keys stop working. Rekeying does not repair a worn plug or housing, and it won't stop a bolt from binding on the frame.

Why might a copy work in a front door but not a mailbox or side door?

A copy that works in one lock but not another is sitting right at the edge of fit. Each lock has its own wear and internal play, so an older, looser cylinder can accept a slightly off cut that a tighter one rejects. Confirm, too, that both locks truly take the same key. If the original works in both, the copy is the weak link.