A key copied from another copy can work worse because the new key is cut to match the source key's shape, including its wear and any small cutting errors. The new cut then adds small errors of its own. Each generation inherits the last one's drift, so a key that already sticks makes a poor pattern. Copy from the original or the least-worn key instead.
How small cutting differences stack up across copies
A pin tumbler lock is the common type with a row of small spring-loaded pins inside the cylinder. It opens when the key lifts each pin to the right height. At that height the pins line up with the edge of the turning plug, a point called the shear line, and the plug can rotate. The cuts along the key blade set those heights.
A duplicate is cut by following the shape of the key you hand over. The copy has no idea what the lock originally wanted. If the source key has rounded peaks from years in a pocket, or one cut sits a little shallow because an earlier copy was slightly off, the new key picks that up. Then the new cut adds its own small variation.
One generation of that usually stays within the play a lock allows. Stack several generations and the differences can add up until a pin rests just above or below the shear line. That is the key that only turns if you pull it out a hair or lean on it.
Which key in your set is closest to the original?
Gather every key for that lock before choosing a source. You are looking for the key with the shortest family tree and the least wear.
Start with history. A key that came with the lock, or one from whoever installed or last changed it, is probably an original or close to one. Originals sometimes carry different stamping on the head than later copies. Treat that as a clue, not proof.
Then use your hands and eyes. Try each key slowly. A good key slides in without catching and turns without coaxing. Hold two keys side by side against a light with the blades lined up. Wear shows as rounded tips where the peaks were once sharp. A bend shows when the blades will not sit flat together. A key that feels clearly different from the others in the same lock is telling you something about its cuts.
Now rank them. Put the original or a known first copy at the top, then the smoothest copies, then anything bent, sticking, or of unknown origin. The top key is your source. The bottom key should not be copied at all.
Picking a source key, or deciding to stop copying
- If the original or a smooth first copy exists, use that key as the source for every new spare instead of copying the newest spare. All the spares then share one parent rather than forming a chain.
- If only worn or sticking copies remain, stop duplicating at that point. Ask a locksmith about options such as a fresh key cut to suit the lock instead of traced from a worn one. Rekeying is another option. It means changing the pins inside the cylinder so a new key fits and the old keys no longer do.
- If even your best key struggles, the lock or door may be part of the problem. That points to repair, rekeying, or replacement, not more copies.
Once a better key is in hand, take the worst one out of circulation. A sticking key left on someone's ring tends to become the one grabbed for the next copy, and the chain starts over.
What to bring when you ask about new spares
A locksmith can only work from the keys and details you provide, so a little sorting at home keeps the conversation short.
- Every key in the set, including the ones that stick
- A note on which key works best and which ones give trouble
- Which lock each key belongs to, if the set covers more than one door
- How many spares you want and who they are for
- Whether the lock itself has been acting up, such as a stiff turn even with the good key
Upper East Locksmith does key cutting and duplication, along with rekeying and lock replacement when the set itself is the problem. To talk through a set like this, call (347) 444-9725.
Frequently asked questions
Is it better to copy the original key or the newest copy?
The original key, or the copy closest to it, is the better source. A newer copy is not automatically better. Newness tells you when a key was cut, not what it was cut from. A shiny key made last month from a worn copy can sit further from the lock's intended cuts than an original that has seen little use. Judge a source key by its lineage and wear, not its age.
If a copy works fine today, is it safe to use as the source for more spares?
A copy that works smoothly today can serve as a source, but it is a weaker choice than the original if the original still exists. A key can open a lock while sitting near the edge of what that lock accepts, and the next copy then has less room to spare. If the smooth copy is the only good key left, use it, and ask about a fresh cut before the set drifts further.
When does a worn key point to a lock problem rather than a key problem?
A worn key points to a lock problem when several keys, including the original or a smooth copy, all feel stiff in the same lock. Another sign is a key that turns easily in a second lock it fits but not in the first one. A key that turns hard only when the door is closed often means the bolt is rubbing on the frame. Those cases call for attention to the lock or door hardware, not another key.
Should I keep an old worn key after I have a better one?
An old worn key is worth keeping only until the replacement keys have opened every lock the worn key opened. After that, the worn key mostly causes trouble. It ends up in a drawer, loses its label, and someday gets handed over as the pattern for a new copy. If you hold on to it, mark it plainly as retired and store it apart from the working keys.