How a key actually works, in brief
A standard pin tumbler key is a small piece of metal with a series of cuts along its blade. Each cut has a depth, and each depth lifts a matching pin inside the lock to exactly the right height. When all the pins line up, the cylinder is able to turn. If one cut is too deep or too shallow by even a small amount, a pin sits at the wrong height and the lock resists.
That precision is the reason key quality matters. The tolerances involved are tiny, measured in thousandths of an inch. A key that is slightly off may still turn in a brand-new lock, because new pins and springs forgive a little error. As the lock ages and its parts wear, the same key may begin to bind or fail. People often blame the lock, when the real cause is that the key was never quite right.
A key is also shaped along its sides, called the profile, which has to fit the keyway of the lock. A blank with the wrong profile will not enter, or will enter but wobble. Even among blanks that fit, the metal, thickness and finish vary.
None of this is mysterious, and you do not need technical knowledge to take sensible steps. The ideas below help you decide when a key is good enough and when to start over from a better source. For basic background on locks themselves, see what rekeying is.
What duplication drift is
When a key is duplicated, the machine reads the shape of the original and cuts the blank to match. No machine is perfect, and no operator is perfect either. A tiny error in the first copy, perhaps from a clamp that was slightly off, a worn cutter or a dirty original, produces a key that is just a little different from the source.
Now imagine copying that copy. The second generation inherits the first copy's errors and adds new ones. A third copy adds more. By the time you reach a key that is the copy of a copy of a copy, the cuts may have wandered enough that the key struggles in the lock. This is duplication drift, and it explains why a key that was cut from an original works smoothly while a key cut from a worn duplicate may not.
The same thing happens with wear. Keys wear every time they are used. The edges round off, the cuts shallow out and the metal burnishes. A key that has been used daily for ten years is no longer the key that was first cut. If you copy that worn key, the copy will begin its life already worn, and with additional machine errors layered on top.
A practical lesson follows: whenever possible, copy from an original or from a key that has seen little use. If your only key is badly worn, a locksmith may be able to cut a new one from the lock itself, using the lock's information rather than the key's, which returns you to a fresh start.
Blanks: the metal you start with
A blank is the uncut key that the machine shapes. Blanks differ in quality. Some are made by the lock manufacturer or a reputable supplier to tight standards. Others are lower-grade imitations that may be thinner, softer or slightly off in profile. A poor blank can bend, wear down quickly or produce cuts that look right but fit loosely.
A mismatched blank is another common issue. A kiosk or a store may stock a general blank that is close to your key's profile but not identical. It may enter the keyway and even turn, but it can bind or wear the lock over time. Using the correct blank for the correct lock is part of getting a good copy.
Material matters for climate too. In South Florida, humidity and salt air corrode some metals, and a key that tarnishes or pits may feel rough in the lock. Brass keys are common and generally hold up well, while nickel-plated or coated keys offer more protection against corrosion but can flake if the plating is poor. If a key feels gritty or leaves residue on your fingers, the metal or the finish is breaking down.
If your key says something like Do Not Duplicate, remember that this is a request and not a barrier. Some systems use restricted blanks that cannot be bought openly, and for those, copies must be ordered through the manufacturer or an authorized dealer. The article on restricted keyways and key control explains how those systems work.
How to test a new key before you trust it
Do not leave a duplicate untested. The test is simple and safe. Stand at the door while it is open, so you cannot lock yourself out, and try the new key in the lock several times. It should slide in smoothly, turn with the same effort as your original and withdraw without catching. Try it with the door open and then with the door closed, and test both locking and unlocking.
Pay attention to feel. If you have to jiggle the key, pull it slightly out, or apply force to turn it, the copy is poor. A key should not need persuading. If the new key works only when held a particular way, treat it as unreliable, since it is the sort of key that fails at the worst time.
Compare the two keys side by side. Hold them together in good light and look at the cuts. The depth and spacing should look the same. Look for rough burrs along the edges, which indicate a poor cut. A key with sharp burrs can scratch the inside of the lock and wear the pins.
If a copy fails the test, take it back to the place that made it and ask for a recut, ideally from the original. Do not force a bad key into the lock, and never use a bent or damaged key. A broken piece inside a lock becomes a bigger problem; see broken key in lock for what to do if that happens.
Why copies of copies are a hidden risk
Many households have a pile of keys with no clear ancestry. One was copied from the original, another from that copy, and another from a copy a former tenant had made years ago. Some work well and others stick. When you have to choose which to carry, you have probably already found the pattern.
The risk is not only inconvenience. A key that struggles puts extra stress on the lock, and a worn lock is a candidate for failure. In some cases, a binding key can bend, and a bent key can break off in the lock, which turns a small annoyance into a service call. If you ever notice a key that has begun to twist or shows a crack, retire it before it fails.
There is also the question of control. Every copy is another key in circulation. The more generations of copies you have, the less certain you are about who holds one. That connects to the discussion in duplicate keys and who has copies. If you cannot account for the copies, a rekey resets the system and gives you a fresh set cut to a known standard.
When to go back to the source
There are times when copying yet another copy is false economy. If your best key is worn and the copies you made from it are not working, the sensible step is to start fresh. A locksmith can often cut a new key from the lock itself, using information from the cylinder, which gives you a key that matches the lock rather than a worn key.
If you want to be sure that old keys stop working, the cleaner answer is a rekey. The locksmith changes the lock's pins to a new pattern and cuts a new set of keys to match, all from a fresh start. Every older key, good copies and bad ones alike, goes out of use. This is also the right step after you move into a new home, after a lost key or after anyone with a key no longer needs access. See rekeying after moving in.
Consider replacing the lock if it is worn out. A lock that has become sloppy will not be repaired by a perfect key. If the keyway is worn, the pins are corroded or the cylinder turns with difficulty, a new cylinder or lock may be the answer. The guide on rekey versus replace locks helps you weigh these options.
For vehicle keys, the story is different. Many car keys include transponder chips and need programming, and a simple cut does not make a working key. See the vehicle guides for those cases.
Practical habits for better keys
Keep one original or low-use key as a master source and treat it like a document. Do not carry it daily. Use it only to cut new keys when needed. A key that lives in a drawer and is used only for copying remains close to its original shape for years.
Label the keys in a way that does not reveal what they open. A small colored cap, a stamped number or a discreet mark helps you tell them apart. Avoid writing an address on a tag.
Have a plan for spares. Decide how many you need and who holds them. Fewer keys means fewer opportunities for trouble. If a spare key sits with a neighbor or family member, make a note of it.
Check keys now and then. Look for bending, cracks, rounded edges or worn cuts. If a key feels different from how it did, replace it before it breaks. Lubricate locks as the manufacturer recommends, and keep the keyway clear of debris. For maintenance ideas, see lock lubricant and maintenance basics.
Working with a locksmith on key cutting
If you want a key cut by a locksmith, bring the best key you have, preferably the least worn. Say what the key is for: a house, a gate, a mailbox, a padlock or a vehicle. For house and business keys, the technician can identify the keyway, choose a correct blank and cut and test the copy on site.
If the key is for a restricted or high-security system, expect to show authorization. A locksmith who handles such keys will ask who you are and whether you may order copies, which is a safeguard for you and the system's owner.
Quotes are given only by phone. For ordinary key cutting, a dispatcher can usually explain how the work is priced. For jobs such as cutting keys from a lock, rekeying or working on a restricted system, an on-site visit may be needed first, and there is a service call charge that is explained before dispatch.
If your keys have become unreliable, or you are unsure which of a pile of copies to trust, call and describe what is happening. A dispatcher can talk you through whether a recut, a rekey or a lock replacement is the better path.
Questions people ask
Why does my new key not turn smoothly?
The most common reasons are a worn original, a blank that is not quite right or a small error in cutting that gets bigger when a copy is made from a copy. The key may also have burrs. Take it back for a recut, ideally from an original or low-use key, and test it with the door open before relying on it.
Is it bad to copy a copy?
It is best avoided. Each generation can add small errors, so a copy of a copy may bind or wear quickly. Whenever possible, cut from an original or from a key that has seen little use. If your only key is worn, a locksmith can often cut a new key from the lock itself and start fresh.
Do all key blanks work the same?
No. Blanks differ in profile, metal and tolerance. A blank that is close but not exact can enter the lock and still bind or wear the pins. Good blanks are made to tight standards for the specific keyway. Using the correct blank is one of the main differences between a good copy and a poor one.
Can a locksmith make a key without the original?
In many cases, yes, for a standard lock, because the key can be cut using information from the cylinder. You will be asked to show that you may authorize the work, such as photo ID and something tied to the address. Vehicle keys with chips need additional steps. Complicated jobs may need an on-site visit.
How much does a key copy cost?
Quotes are given only by phone. Ordinary key cutting is straightforward, and a dispatcher can explain how the work is priced. Work that involves cutting from a lock, restricted keys or multiple locks may require an on-site visit first. There is a service call charge, and it is explained on the phone before dispatch.
When should I rekey instead of making more copies?
Rekey when you cannot account for existing keys, after moving in, after a lost key or when someone no longer needs access. Rekeying resets the lock and gives you a new set cut to a known standard, making all older keys and copies useless. Making more copies of an unknown set adds to the uncertainty.
Describe the situation by phone and we will tell you what the job involves. Quotes are given by phone. Jobs that cannot be quoted without seeing them need a technician on site, and the service call charge is explained on the phone before anyone is dispatched.
Related pages
Telling a good copy from a poor one at the counter
You can learn a lot by looking at a new key before you leave the counter. Compare it with the original. The cuts should line up closely, with the same depth and spacing. The edges should be clean, without sharp burrs that catch your fingers. The metal should look like the blank you expected, not a softer or rougher material. A key that feels different in your hand may behave differently in a lock. If you can, ask to compare the original and the copy side by side under good light, since small differences in the cut depth are easier to see that way.
Test it right there if you can. Insert the key in a lock of the same type, if the shop has one, and turn it. Watch for stiffness or catching. If you are copying a house key, test it at the door soon after. Do not leave the test for weeks. A copy that works in dry weather may begin to bind in humid weather, and you want to discover that while you can still return it. Keep the receipt or note of where the copy was made, so you know where to go back if it behaves poorly after a week or two of use.
Always make your copy from the original, not from a previous copy. If the original is worn, consider having the lock rekeyed so a fresh key can be cut from new specifications. That is the cleanest way to reset quality. When you call us, we explain the scope and any quote before work begins, and we check ownership or authority before cutting keys for restricted systems or changing any lock. If a key feels rough or the cuts seem uneven, say so politely and ask for a second attempt, because a good shop wants the copy to work as much as you do.
Dealing with keys that stick, bend or break
A key that sticks is usually telling you something. It might be dirt in the cylinder, a worn key, a poor copy or a lock that needs service. Try a clean dry cloth on the key and a small puff of graphite-based lubricant in the keyway if the lock allows. Avoid heavy oils, which attract dust and gum up in warm, humid conditions. If the key still struggles, stop forcing it. Never spray heavy lubricants into a cylinder, and do not use cooking oil, because those residues collect dust and make the key harder to turn in the long run.
A bent key should be replaced, not straightened repeatedly. Each bend weakens the metal, and a key that snaps inside the lock turns a small annoyance into a larger repair. If you notice a crack or a twist, treat it as an early warning. Get a new copy cut from the original, or have the lock rekeyed and fresh keys made. Keep a spare original in a safe place if you can, as a clean original makes later copies better and helps if the working key is lost or damaged.
If a key breaks in the lock, avoid prying at the broken piece with household tools. You can push it further in or damage the pins. Call us instead and describe what happened. Please call us to confirm availability. We check ownership or authority before opening or changing any lock, and we explain the scope and any quote before work begins. Tell us what happened as precisely as you can, including which direction you were turning when it broke, so we can plan the right extraction approach.