Why a Copied Key Works on Some Tries and Fails on Others

A copied key that works only some of the time is usually a marginal fit, not a random fault. Somewhere in the pairing of key, cylinder, and door, something sits right at the edge of working: a cut slightly off, a worn original copied faithfully, a tired cylinder, or a latch under load. How and where the copy fails tells you which one.

Why a key that is almost right works some of the time

A typical door cylinder is a pin tumbler lock. Inside, stacks of small spring-loaded pins sit across the plug, which is the part that turns. Each cut on the key lifts one stack to a set height. When all the stacks meet the shear line, the seam between the plug and its housing, the plug can rotate.

A copy cut slightly off leaves a pin hovering just above or below that seam. Small things then decide each try: how far the key went in, which way you leaned on it, how hard the door presses on the bolt. The underlying cause stays the same from try to try, so the hits and misses repeat in a pattern you can read.

A simple log of what changes between tries

You need no tools and no disassembly. For a few days, jot down a line each time a key fails or works only after a struggle. Note:

• Which key: the copy or the original, in the same lock.
• Which lock: whether the copy acts the same in other locks it should open.
• Which step: going in, turning, or coming back out.
• Door position: standing open, or pulled shut and latched.
• What changed the result: pushing the key in firmly, easing it back slightly before turning, or pressing on the door.

Also note whether the original has gotten harder to use lately. A change in the original matters as much as the copy's habits.

Copy, original, cylinder, or door: which does the pattern point to?

Read these as tendencies, not diagnoses. Causes can overlap, and only someone looking at the lock can confirm one. Your log will still tend to lean one way.

The copy struggles in each lock it should open

If the original turns cleanly and the copy needs jiggling in all its locks, suspect the copy. A cut may be slightly deep or shallow, or the shoulder, the stop that sets how far the key goes in, may be off. A copy that only turns after you ease it back a little points the same way.

The copy and the original both feel marginal

When the original has started needing coaxing too, the copy may be a faithful reproduction of a worn key. The tips of the cuts round off with use, and a copy traced from that key inherits the wear.

All the keys are erratic in one lock

If the copy, the original, and any other key for that lock all stick there, while the same copy works elsewhere, look at the cylinder. Worn pins or grit inside can make a cylinder fussy with any key.

It turns with the door open but not shut

If the key turns smoothly with the door standing open and fights you once the door is latched, the key and cylinder may be fine. The bolt or latch may be dragging on the strike plate, the metal plate set into the frame, and the key has to push through that drag. Needing to press or lift the door to get a turn is the tell, and it points to alignment rather than the key.

Before anyone looks at it: what to stop and what to keep

Stop forcing the key. Hard twisting on a key at the edge of working can bend it or snap it off in the plug, and then the problem is a door that will not open. Amsterdam Locksmith offers 24/7 emergency lockout service for that case.

Stop re-copying, too. If your log points to a worn original, more copies from it carry the same flaw, and using that original less slows its wear.

Keep the original, the problem copy, and your notes together for whoever inspects the lock. The recorded pattern helps a locksmith decide whether the keys need replacing, the cylinder needs rekeying, or the door and strike need adjusting. Amsterdam Locksmith works on residential and commercial locks on the Upper West Side, including lock change and rekey and door repair. If you want someone to look at it, call (917) 200-2978.

Frequently asked questions

Is it safe to keep using a duplicate key that sticks sometimes?

A duplicate key that sticks some of the time can stay in use with care, as long as you never force it. Hard twisting on a marginal key can bend or break it inside the cylinder and lock you out. Keep the original handy as a backup, and if the copy keeps needing more effort, retire it and have the keys and lock checked.

Should I try lubricant when a copied key works intermittently?

Lubricant is not the first step for a copied key that works intermittently. If the copy is cut slightly off, lubricant will not change where the pins land, and it can mask the pattern you are trying to read. Finish comparing keys and locks first. If all the keys stick in one lock, that cylinder is worth having inspected.

If a copy works in the lock only some of the time, does the lock need to be rekeyed?

Rekeying is not automatic when a copy works only some of the time. If the original turns cleanly and only the copy struggles, the copy is the likelier issue. Rekeying, which means changing the pins in the cylinder so it works with a new key, makes more sense when all the keys are erratic in that lock or the original itself has worn badly.