A newly cut key that won't turn in your lock is frustrating—and expensive to fix if it damages the mechanism. Understanding why duplication fails helps you avoid costly mistakes and know exactly what to demand from a locksmith or key-cutting service. Here's what actually goes wrong, and how to prevent it.
The Original Key Is Worn or Damaged
The most common culprit behind failed duplications is a worn original key. Over years of use, keys develop micro-scratches, rounded edges, and subtle grooves that no longer match the lock's precise tolerances. When a machine traces a worn key, it copies those imperfections directly onto the blank.
Check your original key before handing it over. Look for visible damage along the cutting edge, discoloration, or bending. If it's visibly worn, ask the technician to examine it under magnification. A reputable locksmith will flag this issue upfront rather than duplicate a compromised key and charge you again to fix it.
Incorrect Blank Selection
Keys look similar, but blanks for different manufacturers have vastly different internal profiles. A Schlage blank won't work in a Kwikset lock, and trying to force it can scratch your lock's interior. Some service providers cut corners by using cheaper universal-fit blanks that don't match your specific lock brand.
Always confirm your lock's brand and style before dropping off your key. Bring documentation if you have it—a lock box label, manufacturer paperwork, or even a photo. Reputable services like those found on Mercoly clearly specify which blank they're using and cross-check it against your lock type.
Calibration Issues in the Cutting Machine
Key machines require regular calibration. A machine that's even 0.5 millimeters off will produce a key that binds or won't turn at all. Older machines, or those servicing high-volume shops without proper maintenance schedules, drift out of tolerance over months.
Ask how often the service tests and recalibrates their equipment. Quality shops perform test cuts on sample blanks weekly or after every 50–100 cuts. If they can't tell you their maintenance schedule, that's a red flag. Expect to pay $15–$30 for a standard house key cut from a well-maintained service; significantly cheaper providers may be skipping maintenance.
Depth or Spacing Errors During Cutting
The spacing and depth of each cut must be exact. A cut that's 0.25mm too shallow means the key won't engage the lock's pins fully. A cut that's too deep can jam the mechanism. Poor technique, dull cutting bits, or operator error introduces these mistakes.
This is why some locksmiths test-fit the key in a practice lock before handing it to you. If your service doesn't offer this, ask them to. The extra 2–3 minutes is worth catching a bad cut before you take it home and potentially damage your actual lock.
Misread Original or Wrong Profile Copy
Hand-reading errors still happen, especially with worn or unusual keys. An operator might misinterpret where a cut begins or ends, or confuse a shallow cut for a non-cut section. Digital scanning and laser-based systems reduce this, but even automated tracing can fail if the original key is placed at the wrong angle.
Position your original key carefully in the machine, ensuring it sits flush and parallel. Watch the technician set it up. If they seem rushed or place it carelessly, speak up.
Material Defects in the Blank
Occasionally, a blank itself is defective—soft spots in the metal, inclusions, or manufacturing flaws that cause the key to shatter or snap during cutting. This is rare with reputable manufacturers, but bulk-buy cheap blanks increase this risk.
Ask which blank manufacturer your service uses. Established brands like Ilco, Weiser, and Baldwin have quality controls. Budget blanks from unknown sources are a gamble.
What to Do If Your Duplicated Key Fails
Don't force a stuck key into your lock—you could damage the lock's internal pins. Take the key and original back to the service and ask for a recut at no charge. Most legitimate shops guarantee their work.
Frequently Asked Questions
Q: How do I know if my original key is too worn to duplicate accurately? If your original key requires visible wiggling or jiggling to turn the lock, or if it has visible scratches, pitting, or edge rounding, it's too worn. Ask the locksmith to examine it under magnification before proceeding.
Q: What's the typical cost range for standard residential key duplication? Most locksmiths and key-cutting shops charge $2–$5 per standard house key, with specialty or high-security keys running $10–$30 each depending on complexity.
Q: Should I get multiple copies made at once, or one at a time? Getting 2–3 copies at once is cost-effective and lets you test one before relying on the others, catching any machine drift early.
Use Mercoly to find and compare trusted key-cutting and duplication providers in your area.