Rekeying a lock to match an existing key

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  #1  
Old 11-02-15, 05:50 PM
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Rekeying a lock to match an existing key

So I have a key for the main house front door locks, another key for the back door locks, and a third set of keys for the guest house.

I also have a master key that opens all three set of locks.

I took off the back door locks, took it to a local locksmith. I gave him the key for the front door, and ask him to rekey the set of back door locks to the same key as the front door locks.

He said fine, he can do that, it will be $30 for the pair of locks to be rekeyed. Once that's done, the front and back door locks would use the same key.

Now I asked the locksmith to make sure my master key, which works for front door, back door and the guest house, would continue to work. He said no, once he made the back door locks match the front door locks, they have to work the locks so it would work for the master key as well, and that would be additional $20.

Now this is what I don't understand. If the master key already works for front, back and guest, and now I am just changing the back door locks to match the front door locks, why would the master key not work anymore? That makes no sense to me.
 
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  #2  
Old 11-03-15, 10:15 AM
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You're making the back door locks match ONE key, not two. Master keyed locks have additional pins so that there are multiple combinations of key cuts which will open them.

That said, any credible locksmith knows this and should be able key the lock to work with both keys but I can see him asking more money to do it since the job is more complicated.
 
  #3  
Old 11-03-15, 09:23 PM
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He is correct for charging you to fit both the individual key and the master key. Yes I know the master key fit all along, but a change of the individual key (called the "change key") requires a different set of bottom pins, but also requires a new set of master pins, so there's still labor to fit both keys.

I think the additional charge for masterkeying is a little high tho...$15 per cylinder for normal rekey is about right but the add-on to masterkey shouldn't be more than $3-$5 per cylinder.
 
  #4  
Old 11-03-15, 11:50 PM
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Thank you both for the replies.

The money is not a major issue. What is puzzling to me and I am just trying to get it right in my head. I am not getting it.

Front door - A
Back door - B
Guest house - C

I have individual keys for locks A, B and C. I have a master key that opens A, B, C.

In my mind, by asking him to rekey B to match the key of A, I am basically asking him to duplicate the cylinder pins in B to be the same as that of A, right? At the end, all I am doing is eliminating B altogether.

So why would a master key that worked on A, B and C all of a sudden not work on just A and C?

I know I am missing something here, I need to learn what I am missing. Unless what you are saying is, when he rekeyed B to match A, the key for A will work for the rekeyed locks, BUT the pins inside the rekeyed locks do not necessarily match the pins of locks A?
 
  #5  
Old 11-04-15, 07:49 AM
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If I were rekeying your lock I would dump the pins in the plug and when checking top pins and springs in the housing, I would dump any master pins I might find. If you didn't also give me your Master Key or tell me you wanted it to still work, how would I know? Believe me, there are a lot of cylinders with master pins out there that the end user doesn't know about.

You may need to understand what goes on inside a lock cylinder, which we'll just call the cylinder. Figure 1 is an exploded view of a representative 5-pin cylinder; 5 bottom pins, 5 top pins and 5 springs. When the plug is inserted into the housing, nothing stops it from turning; that's what the pins do. A bottom pin, top pin and spring reside in each pin chamber (s set of corresponding holes in the housing and plug).

Figure 2A is a view through the cylinder, like an x-ray, showing the housing, plug and cylinder shear line. For illustrative purposes only 1 pin chamber is used. The shear line of the cylinder is where the outer diameter of the plug meets the inner diameter of the housing. We've loaded a bottom pin, top pin and spring in the 1st chamber and where the top and bottom pins meet is the shear line of that chamber.

With no key inserted in the plug the top pin blocks the shear line, keeping the plug from turning. If a key cut to the proper depth (lets say the cut depth is 3) is inserted, it will push the bottom and top pins up to where the shear line of that chamber matches the shear line of the cylinder and the plug will turn. If the key is cut too shallow (a 1 or a 2), the bottom pin is raised too high, it blocks the shear line and the plug won't turn; too deep (4, 5, ...), the bottom pin isn't raised enough, the top pin blocks the shear line and the plug won't turn.

In Figure 2B a master pin has been added; let's say it's a number 2. Now that chamber has 2 shear lines, so there are 2 keys that operate the cylinder; one with a 3 cut and one with a 5 cut (#3 bottom pin + #2 master pin = 5). Now you can apply the same principal to as many chambers as needed.

I hope I have properly communicated these principals so you can understand them. And that's what it boils down to; communications. Just as you have to communicate to your mechanic that you want a tune-up in addition to that oil change, you also have to communicate to the locksmith exactly what you want.
 
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  #6  
Old 11-04-15, 10:28 AM
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He's not rekeying B to match A, he's rekeying B to match the KEY A. The additional charge is to rekey B to match A based on the actual pins.

Another way of saying this is the standard process is to key a lock to a key. You're being charged more because you're asking him to key a lock to a lock.
 
  #7  
Old 11-04-15, 02:30 PM
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Your questions, in order of appearance: 1) Yes, the pins in lock B will be changed to match the pins in lock A. 2) The master key will work on B since it has the same pins as A. 3) Yes, the pins will match.

I think what you're asking is why there is one charge to rekey lock B to fit key A, and another charge to rekey lock B to fit the master key, when said master key has not changed.

The answer is that the process of changing the settings (pins) in lock B to match key A results in a change to the master key settings, thereby requiring a separate labor charge to restore the original master key settings.

The image provided by ThisOldMan should help you see the relationship between bottom pin, master pin and top pin.
 
  #8  
Old 11-06-15, 10:14 AM
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this is a common misconception about master key systems by the consumer.

A master key system is built into the lock cylinders not governed by the keys.

each lock must be deliberately keyed to a system produced for the entire project. you cannot just match a lock to a key and expect it to work without complication (you can, but that is advanced locksmithing - and not for this forum in my opinion).

However, i do regularly key up cylinders to separate change keys and a master key, but when the system requires changing it is best to rekey all cylinders in the system, not just the one or two you want to do.

Depending on the type of system, certain systems have greater master keying flexibility than others and more permutations available.
 
  #9  
Old 11-06-15, 09:53 PM
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Since OP's situation only includes 3 locks, it is possible, or even likely (if a locksmith originally keyed these up) that only 1 pin chamber was masterkeyed, in which case the additional labor charge should really only be a few bucks, in that the time to select, even by trial-and-error, the correct single master pin would not take more than one minute.
 
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