Why a copy of a copy stops working
Key cutting is a duplication process, and duplication accumulates error. A machine tracing your original follows the existing cuts with a stylus and reproduces them on a blank. Every trace introduces a small deviation — stylus and cutter wear, a fraction of play in the vice, a burr left on an edge. Copy from an original and the deviation is negligible. Copy from a copy, then copy that, and the deviations stack in the same direction until a cut sits far enough off its intended depth that the pin it lifts no longer reaches the shear line.
Worn originals make this worse. A key carried on a ring for eight years is measurably smaller than the day it was cut — brass abrades against steel every time it enters a keyway, and the peaks of the cuts round off first. A copy of that key faithfully reproduces the wear, and then adds its own error on top. This is why the honest answer to "my new key doesn't work" is often "your old key was already at the edge, and we should cut a fresh one from the code instead."
Cutting to code, and why it produces a better key
Every lock cylinder has an intended cut specification — a sequence of depths at defined spacings. Cutting to code means setting those depths directly from the specification rather than tracing a physical key, which removes accumulated error entirely and produces a key at the centre of tolerance. Where the code is not on hand, a technician can decode the lock itself by reading the pin depths and generate the same result. Both routes give you a key that works better than the one you have been using.
Blanks: the part that decides whether a key can exist
A blank is the uncut key, and it has to match the lock in more ways than people expect. The keyway profile — the pattern of grooves and ribs running along the blade — has to slide into that specific cylinder. The blade length, thickness, tip and shoulder position must be right, since the shoulder is what sets the key's depth reference in the machine and in the lock. Get the profile right and the shoulder wrong and the key enters the lock but every cut lands in the wrong place.
Identifying a blank is a skill rather than a lookup. A technician reads the keyway cross-section, the bow shape, any manufacturer stamps, and the number of cut positions, then matches it to a blank family. Old, imported and discontinued hardware is where this earns its keep — a lot of the hardware still in service on older properties, sheds, cabinets, gates and furniture is on keyways that no kiosk carries and no self-service machine recognises.
Types of cut you will run into
- Standard edge cut. The familiar jagged profile along one edge of the blade. Cut on a conventional machine, widely duplicated.
- Double-sided. Symmetrical cuts along both edges so the key works either way up. Common on newer residential and cabinet hardware.
- Laser or sidewinder. A wavy track milled into the flat face of the blade rather than the edge. Needs a milling machine, not a conventional cutter, and is standard on most modern vehicle keys.
- Dimple. Round depressions drilled into the faces at varying depths. Found on many high-security and European cylinders.
- Tubular. The circular key used on vending machines, coin boxes, some cabinet and bike locks. Cut on dedicated equipment.
Restricted and controlled keys
An ordinary residential blank is available to anyone. That is the whole basis of convenient duplication, and also the reason key control does not exist on standard hardware — a key handed to a cleaner or a contractor can be copied on the way home and returned looking untouched.
Restricted and patented keyways change the economics. The blank is controlled by the manufacturer and distributed only to authorised holders, so copying requires going through a channel that keeps a record and asks for authorisation. Practically, that means a property owner can issue keys and know that the number in circulation is the number they issued. For a managed property, a rental, an office or a storage building, that is usually worth more than any additional physical strength in the cylinder.
Two honest caveats. A restricted system requires you to keep records — the control only works if someone maintains the authorisation list. And restricted keys take longer to obtain than a walk-in duplicate, so plan spares in advance rather than in an emergency.
Broken keys, and what not to do about them
Keys snap for predictable reasons. Brass work-hardens and fatigues where the blade meets the bow, especially on a key used to pull a sticky door closed or turned hard against a bound bolt. A blade that has been bent and straightened has a crack waiting at that point. And a cylinder that resists turning puts the whole load through the narrowest section of the key.
When a key breaks off in a lock, the two instincts that make it worse are pliers and glue. Pliers on a stub that is not protruding push the fragment deeper and score the plug. Glue is worse — it bonds the fragment to the pins and converts an extraction into a cylinder replacement. Leave it alone. A technician has extractors made for this and can usually remove the piece and return the lock to service.
Once the fragment is out, the important part is figuring out why it broke. If the cylinder is stiff, the next key will break too. If the door binds and people are using the key as a handle, the door is the fault. If the key was simply worn and fatigued, a fresh key cut from the code is the cure.
Making one key open everything
A very common WaterColor situation: front door on one key, back door on another, garage service door on a third, storage room on a fourth, and one key on the ring that gets used. Rekeying the cylinders to a common key is straightforward provided the locks share a compatible keyway, and it removes the daily friction that makes people prop doors and hide spares.
Where keyways differ, the usual route is to change cylinders rather than whole locks, keeping the existing hardware and finish. It is worth doing at the same time as any rekey after lost keys or a change of occupancy, because the cylinders are already being serviced.
Key hygiene that prevents most of our call-outs
- Keep one key out of circulation. A reference key that lives in a drawer and never gets carried stays at its original dimensions, so future copies come from an unworn source.
- Replace worn keys before they fail. If a key needs jiggling, lifting or a particular angle to work, it is telling you it is at the end of its accuracy. That is a five-minute fix on a good day and a lockout on a bad one.
- Don't put the address on the tag. A key that identifies its own door is a different object from a key.
- Stamp codes, not names. On a property with several keys, mark them with a code and keep the meaning of the code somewhere else.
- Count what is out. If you cannot say how many working copies exist and who holds them, the number is effectively unknown, and rekeying resets it to a number you chose.
- Keep the keyway clean. A dry lubricant occasionally; not oil, which holds the salt and grit that our air delivers free of charge.
Keys for the things that are not doors
A large share of shop work is not house keys. Filing cabinets and desks, tool chests, gate and shed hardware, storage lockers, cam locks on cabinets and display cases, luggage, furniture, and the miscellaneous locks that came with a property and no keys. Most of these can be handled either by cutting to code from a number stamped on the lock face or plug, or by decoding the lock and generating a key. Where a cam lock has no code and no key, replacing the core is usually quicker and cheaper than recovering the original.
What to bring or tell us
For a duplicate, bring the best key you have, not the one on your ring — if there is an unworn spare in a drawer, that is the one worth copying. For a key by code, bring the lock, the removable core, or the code if it is stamped or documented. For obsolete or unfamiliar hardware, a clear photograph of the keyway and any stamped numbers usually lets us confirm whether a blank exists before you make a trip. And if a key is failing rather than missing, say exactly how it fails — will not enter, enters but will not turn, turns partway, or works on one door and not another. Each of those points somewhere different.
Common Questions
Why doesn't my new copy work when the old key does?
Because it was probably copied from a worn key. Duplication traces the original including its wear, then adds a little error of its own, and eventually a cut sits too far off depth for the pin to reach the shear line. Cutting a fresh key to the lock's code instead of tracing removes the accumulated error.
Can you make a key when I have no original at all?
Yes. Either from the lock's key code where one exists, or by decoding the cylinder itself and generating the cut from the pin depths. Both produce a key at the centre of tolerance, which usually works better than the key you lost.
What is a restricted key and should I have one?
A restricted key uses a blank the manufacturer controls, so copies can only be cut through an authorised channel that keeps a record. It is worth it wherever keys circulate among people who are not permanent occupants — rentals, offices, storage. On standard blanks anyone can copy a key without you knowing.
My key broke off in the lock. Can it be saved?
Usually. A technician can extract the fragment with the right tools and return the cylinder to service. Do not try pliers on a stub that isn't protruding and never use glue — glue bonds the fragment to the pins and turns a small job into a cylinder replacement.
Can you cut a key for an old cabinet or shed lock with no markings?
Often. The blank is identified by the keyway profile, blade dimensions and shoulder position rather than by markings, and a photograph of the keyway plus any stamped numbers is usually enough to confirm whether a blank exists before you make a trip.
Can all my doors use the same key?
Usually yes. Where the cylinders share a compatible keyway, they can simply be re-pinned to one key. Where they don't, swapping cylinders rather than whole locks gets you there while keeping the hardware and finish you already have.
See all FAQs →