What a key copy actually has to do
A key works by lifting each pin inside the lock to exactly the right height. The cuts along the blade are the instructions: each cut has a specific depth and sits at a specific spacing from the shoulder. If a copy has even a tiny error in one cut, one pin will sit slightly high or low, and the cylinder will not turn. The margins are small, often measured in thousandths of an inch, which is why a copy can look identical and still fail.
A duplicate is made by tracing an existing key on a machine and cutting a blank to match. That tracing step is where errors enter. The machine must grip the original and the blank in precisely the same position, the tracing guide must be clean and accurate, and the cutter must be sharp. If any of these steps is off, the new key inherits the error, and it may be slightly different from the original.
Keys also have to match the lock's keyway, the shape of the slot the key slides into. The blank must have the same profile as the original, or it will not enter, or it will enter but bind. Many keys look alike but belong to different keyways, and some brands have several similar profiles. Choosing the wrong blank is a frequent cause of copies that stick or refuse to insert.
Worn originals produce worn copies
A key that has been used for years develops rounded peaks and shallow valleys where it has rubbed against the pins. If you copy that worn key exactly, the copy carries the wear. The new key, however, is cut from a fresh blank that is sharper and does not behave like the old one. A lock that has also worn to match the old key may accept the original but reject the copy.
This situation is common in homes where the same key has been used for decades. The lock and key have worn together, and they tolerate each other. Introduce a new, accurately cut key and the fit is different. The lock may feel stiff or fail to turn, even though the copy is cut correctly. The cure is often to service the lock, not to blame the copy.
If your key is visibly worn, polished, or bent, treat it with caution. Do not use it as a master for many copies. A locksmith can sometimes cut a new key by taking the lock's measurements directly, or by decoding the key based on the lock's design, producing a key closer to the factory specification. That key works better than a copy of a tired original.
- Worn originals pass their errors to every copy.
- A new key may expose a lock that has worn to fit the old one.
- Avoid making copies of copies.
- Retire keys that are bent, rounded, or smooth at the cuts.
Blank mismatch and keyway errors
Blanks come in hundreds of profiles. Two blanks that look the same to the eye can differ in the shape of the grooves along the blade, the length, the shoulder position, or the bow. A blank that is slightly too thick will not enter the keyway. One that is slightly too thin will rattle and may not lift the pins evenly.
Mismatches are more common with brands that have several similar keyways, and with high-security or restricted keys that have unusual profiles. A hardware store may stock only the most common blanks, and an employee may choose the closest one. The result is a key that is cut correctly but built on the wrong foundation.
Another issue is the blank itself. Quality varies between manufacturers. A soft or poorly made blank deforms with use and loses its shape. If a new copy worked at first and then began to fail, the metal may be at fault. A locksmith will usually use a reputable blank matched to the lock's brand and keyway.
Machine and operator errors
Key cutting machines need careful setup. The original key must be seated against the shoulder or the tip stop, depending on the key, and held tight in the vise. If the original is placed slightly crooked, every cut is slightly off. If the blank is not seated against the same stop, the spacing is wrong. These are easy mistakes to make, particularly in a busy store.
Cutters and tracing guides wear down. A dull cutter leaves burrs on the cuts, and burrs catch on the pins. A worn guide gives inaccurate tracing. Machines that are not calibrated or that are cleaned rarely produce poor results. A good shop keeps its machines in order and deburrs each finished key.
Some customers find that a self-service kiosk produces copies with higher failure rates than a staffed counter. Kiosks do fine on simple keys in good condition, but they have little tolerance for worn originals or unusual profiles. If your key is anything out of the ordinary, take it to a professional who can inspect it and check the finished key against the lock.
What to try before blaming the copy
Before returning the key, test it in good conditions. Try it in the lock with the door open, so the latch or deadbolt is not under pressure. Insert the key fully, pull it back slightly, and try to turn gently. Many locks need the key to be positioned precisely, and a key that is not pushed in all the way fails. If it still does not turn, try the original in the same way to compare feel.
Look at the key. Are there burrs along the cuts? Do they feel sharp or rough? Light burrs can sometimes be removed with a gentle pass of a fine file or a stiff brush, but be careful. Filing the cuts changes their depth, so unless you know what you are doing, leave it to the shop. Compare the new key and the original side by side. If any cut looks visibly different, take it back.
Try the copy on other locks of the same brand, if you have them. If it works in another lock but not in the intended one, the lock may be worn or dirty. If it fails everywhere, the copy is probably at fault. Bring both keys and the lock details to the shop and explain what you tried.
How a locksmith fixes a bad copy
A technician starts with the lock. A key that will not work may reveal that the lock is worn, dirty, or damaged. The technician can inspect the cylinder, test it with the original, and judge whether it is in good shape. If the lock is fine, they can cut a better key. If the lock is worn, they may suggest cleaning, rekeying, or replacement.
To cut a better key, a locksmith may use a calibrated machine, a quality blank matched to the keyway, and a careful process that includes deburring and test fitting. For some locks, they can create a key from the lock itself by measuring the pins, or by using the original key with careful inspection. This reduces the chance of copying errors.
Many technicians test the new key in the lock before they leave. They may also fine-tune the key by adjusting a cut slightly, a process that takes skill. If the lock is worn, they can explain why a perfect key may still feel tight. We do not give lock-bypass instructions, and nothing here is intended to help anyone get into a lock that is not theirs. The goal is a key that works smoothly for the person entitled to use it.
Smart keys, transponders, and high-security keys
Not every copy problem is a mechanical one. Car keys with transponder chips need programming as well as cutting. A blade cut perfectly will still not start the engine if the chip is not programmed. Push-button start fobs are programmed to the car and cannot be duplicated by cutting alone. If your car key copy turns the door lock but does not start the car, it is likely a programming issue.
High-security keys, such as those with sidebars, dimples, or restricted keyways, cannot be copied at most hardware stores. They are produced under controlled processes, and the shop must verify ownership. If a store tells you that your key cannot be copied, that is by design. A locksmith who handles restricted keys can explain the process and help you order authorized copies.
Smart locks and keypad locks add another layer. If you have a lock with a backup key, the key is mechanical and can be copied like any other, but the smart features have their own credentials. A key copy will not add a new user PIN or fob. Those are set up through the lock's app or programming mode.
Getting good copies in the future
The best rule is to copy from a good key. If you have an original that is clean and straight, use it. If you have only worn copies, ask a locksmith to make a new key from the lock or from a careful decode, rather than copying the worn one again. Keep one original in a safe place and use copies for daily use, so the original stays in good condition.
Choose the shop with care. A staffed counter with a clean machine and a test lock is better than a rushed kiosk, especially for unusual keys. Ask whether they test the copy in a sample cylinder or in your lock. Ask about the blank quality. A reputable shop will answer plainly.
Before you leave the store, try the copy in your own lock if you can. Take a moment to test it at the door. A copy that fails in the first minute is much easier to return than one that fails after days or weeks. If the shop is a mobile service, the technician can test it in your lock on the spot.
- Copy from a clean original, not from another copy.
- Ask the shop to test the key before you pay.
- Keep one original in a safe place.
- Take restricted keys to a shop that handles them.
Locks that wear out and tell you so
Sometimes the copy is fine and the lock is the real problem. Signs of a worn lock include a key that must be wiggled to turn, a lock that works only with one particular key, a cylinder that feels gritty, or a key that slides out slightly when turned. In coastal Florida, salt air and humidity speed this up, particularly on outdoor locks.
In that case, the repair may be cleaning and lubricating the lock, replacing worn pins, rekeying, or replacing the cylinder. A new key will then fit well and last longer. It makes little sense to cut copy after copy for a lock that is failing.
If you are having key trouble, call and describe it. Bring the key, the copy, and the lock details. A technician can help you decide whether the fix is a better key, a repair, or a new lock. Quotes come by phone, and complicated jobs may need an on-site visit.
Questions people ask
Why does my new key work in the shop but not at home?
Shop locks are clean and often tolerant. Your own lock may be worn, dirty, or tuned to your old key. Test with the door open, and compare how the original feels. If the original works smoothly and the copy sticks, take the copy back. If both feel rough, the lock likely needs service.
Can a worn key be copied successfully?
Sometimes, but the copy carries the wear and may behave differently from the original. A locksmith may be able to cut a new key from the lock itself or from careful measurement, which gives a better result. Avoid making many copies from a tired key.
Why can I not copy my high-security key at a hardware store?
Restricted keys are protected so that copies are made only with ownership checks. That is a deliberate security feature. A locksmith who handles restricted keyways can explain the process, check ownership, and order authorized copies for you.
My car key copy opens the door but will not start the car. Why?
The engine needs a programmed transponder chip in addition to a correctly cut blade. Cutting alone does not make a working key. A locksmith with programming equipment can program the chip to your vehicle after confirming ownership. Bring registration and identification.
Should I file the key to make it fit?
No. Filing changes the cuts and can make the key worse or ruin it. Burrs can sometimes be cleaned gently, but if the copy does not work, return it to the shop or have a locksmith adjust it. Do not force a stiff key in the lock.
How is the price decided?
Quotes are given only by phone. Simple key work can often be quoted from your description. Complicated jobs may need an on-site visit before a quote can be given. There is a service call charge, explained on the phone before dispatch. Ask questions so you know the arrangement before anyone arrives.
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.
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Testing a new key before you leave the counter
The cheapest time to catch a bad copy is while you are still standing at the shop. Ask to try the key in the lock it is meant for, if the shop is nearby, or bring the lock to a place where you can test it. At a minimum, insert the copy into the original lock a few times and turn it fully. It should slide in smoothly, turn without extra force, and come out without catching. Any hesitation at this stage is a sign that the cut is slightly off. Taking a few minutes to describe the situation clearly before the visit usually makes the whole job go more smoothly.
Compare the two keys side by side. Hold them together against a light and look at the profile and the depth of the cuts. The copy should have the same shape and spacing as the original, with no burrs or rough edges. Run a fingernail along the cuts to feel for sharp spots, and ask the shop to clean them if they are present. A burr left on a fresh key can drag on the internal pins and cause a sticking feel that gets worse with use. The rainy season, with its heavy downpours and daily humidity, is a good moment to repeat the check and compare notes.
Also test the key in the rest of the locks it is supposed to open, such as the knob, the deadbolt, and the garage entry. A key can work in one but not another when a lock is worn or misaligned. If something feels wrong, return it promptly and explain what you tested. The shop can recut it, or suggest that the problem is the lock. A technician can look at the lock and explain the cause, with the scope and any quote explained before work begins. Small details such as a slightly sticky bolt or a faint grinding sound are often the earliest hints worth acting on.
What to do with a key that almost works
A copy that works only when you jiggle it is a nuisance, and it is also a warning. Over time, the jiggling wears both the key and the lock. Resist the urge to force it, and do not use pliers or heavy pressure. Instead, stop using that copy for daily needs and keep it aside. Use the original only if it works smoothly, and ask a shop to make a fresh copy from the original, not from the problem copy, since errors multiply when copies are made from copies. Ask questions at any point, and expect plain answers about what is being done and why.
If the original also feels rough, the issue may lie in the lock itself. Dirt, worn pins, or a damaged cylinder can make even a good key feel hard to turn. A small amount of the right lubricant sometimes helps, but too much or the wrong kind can make things worse. When the trouble persists, a technician can inspect the cylinder, explain what is wrong, and propose a repair or a replacement. The scope and any quote are explained before work begins. Neighbors and family members who share the property should know the plan, especially anyone who may arrive home late.
Keep a short record for future copies. Note which shop made the copy and which blank was used, if you can. Keep one reliable master key stored away and use it only to make duplicates. That habit protects you from the slow drift in accuracy that comes from copying copies. When a key and lock have worn together over many years, replacing the lock and cutting fresh keys is often the cleanest fix and can save repeated trips. Sun and heat can warm metal and plastic parts enough to change how they feel, so test at different times of day if you can.