A copied key that works only sometimes usually has a marginal fit. The key lifts the lock's pins close to the right height but not quite, so small changes in how you insert or turn it decide whether the lock opens. The source can be the copy, the lock, or the door and how it is used. When and where the key fails tells you which is more likely.
Why a key that works only sometimes is not random
Most door locks use a pin tumbler cylinder, which holds a row of small spring-loaded pins, each split in two. The cuts on a key lift each pin to a set height. When every split lines up with the edge of the plug (the part that turns), the lock opens.
A key cut exactly right lines up all the pins once it is fully in. A key that is slightly off leaves a pin or two just past that line, and the outcome then hangs on small things: how deep the key sits, a slight pull outward, a little lift as you turn. That is a marginal fit. It only feels random.
What to notice before deciding anything
These checks need no tools. Use normal pressure. If the key will not turn, take it out and try again instead of pushing harder.
- Try the original and the copy in the same lock several times each, and note which one fails.
- Try the copy in any other lock it should open.
- Turn the key with the door open, then with it closed.
- Notice whether the copy needs to be pushed fully in, eased back slightly, or lifted or pressed on the bow, the part you hold.
- Feel how the key goes in: smooth, gritty, or catching at one spot.
- Hold the two keys side by side and look for rounded cuts or rough edges on either one.
Jot down what you find. A short note like "original always turns, copy sticks in both doors" is worth more than a general complaint that the key is acting up.
Copy, lock, or door: how the patterns differ
The copy is slightly off
If the original turns smoothly and the copy struggles in the same lock and in other locks it should open, the copy is the likely suspect. A cut that is too shallow, too deep, or out of position carries the same error into each lock the copy enters.
The lock is worn or dirty
A lock fault usually troubles the original key too. The original hesitates or feels gritty, and the problem gets worse over time. Worn pins and debris affect any key, so a copy with its own small error simply fails first.
The door is part of it
Sometimes the key turns freely with the door open and struggles only when the door is closed, or only when you push or pull on it. Then the cylinder is probably fine. The bolt is dragging against the strike plate in the frame, and you feel that drag through the key.
The copy inherited wear from the original
Here both keys work, but the copy is worse. An original key carried for a long time develops rounded cuts. A duplicate traced from it reproduces that wear plus whatever small error copying adds, and a copy made from another copy stacks the errors further.
Treat any of these readings as a strong hint, not a verdict. Causes can overlap, and the pattern alone cannot confirm which one you have.
What to do next, and what to leave alone
Stop forcing the copy. Bending or filing a key weakens the blade, and a key that snaps inside the cylinder turns a nuisance into a door you cannot open. Skip lubricant guesswork too: if you do not already know what your lock takes, leave it alone.
Keep the original key somewhere safe, and do not make more copies from it until you know whether its wear is part of the problem.
Bushwick Locksmith & Key Copy offers mobile locksmith service for homes and businesses in Bushwick and nearby neighborhoods such as Ridgewood, Bedford-Stuyvesant, and East Williamsburg. You can describe the problem through the contact section at bushwick-locksmith.com. Your notes are what make that description useful:
- which key fails, the copy, the original, or both
- which locks it fails in
- whether the door position changes anything
- how the failure feels when it happens
If the trouble turns out to be in the lock, a repair, a lock change, or a rekey may follow, depending on its condition. If you are already locked out, 24/7 emergency service is the route instead.
Frequently asked questions
Can a copied key wear out the lock faster?
A copied key with rough edges can scrape the pins and keyway each time it goes in, and a key that needs jiggling adds wear with each attempt. A clean, accurate copy behaves much like the original. If a copy feels gritty or catches on the way in, that roughness is a reason to stop using it.
Is it worth keeping a copy that only works sometimes?
A copy that works only sometimes tends to fail at a bad moment, and the jiggling it needs invites forcing. Keep it out of daily use and never rely on it as your only key, especially for a door you cannot afford to be stuck outside of.
Does a key that works intermittently mean the lock needs replacing?
An intermittent key does not by itself mean a lock needs replacing. The key or the door can produce the same symptom as a worn cylinder. A lock that is worn or damaged inside may need repair or replacement, but you only learn that by checking the lock itself.
Can a rekey fix keys that no longer work well in a lock?
Rekeying resets the pins inside a cylinder to match a new key, so the old keys stop working. It does not repair worn keys or worn parts inside the cylinder. It changes which key the lock answers to. Whether rekeying suits a lock depends on the cylinder's condition, since a badly worn one may need repair or replacement instead.