The process of rekeying a lock allows the lock to be adjusted, so it works with a new key. Rather than changing your locks, the locks are kept the same and merely adapted to fit the key change. With the basic understanding of a pin and tumbler lock (described above) understanding the lock rekeying process is quite simple. It is however, a process that takes time and practice to master, and a single misstep might ruin the lock.
The first things that are needed are the current key, the lock, and the new key that you wish the lock to fit. For deadbolts the apparatus is disassembled by unscrewing, but door knob locks are more complicated. Locksmiths will have other necessary tools for door knob locks, such as a catch tool, a spanner, and a plug follower (sometimes referred to simply as a follower).
The catch tool is used to remove the knob or handle from the lock. To do this, the handle or knob must be twisted until the hole in the knob rose (the sheath-like case usually attached to the wall) is seen. The catch tool is place in the hole to release the catch, and the knob and rose can be separated. The spanner is used to remove the cap (also known as shank) from the knob and the lock cylinder can now be independently accessed.
The spanner is used again to remove the c clip (named because of its c shape) from the plug. The current key is then placed in the keyhole and turned to a 90 degree angle, opening the lock so it may slide free of the plug. The plug follower is positioned on the back of the lock and follows the cylinder as it is ejected. This keeps all the driver pins and springs in place while the rekeying is being done. The plug (part with the key inside) is now separated from the bible (part with the follower inside), and the current key pins are removed from the plug.
A key decoder can be used to find the maker’s specific key pin to groove number ratio. The grooves are measured in accordance with the company specification of groove depth, and this corresponds to a number. Once the groove numbers are measured, the company’s list of relative heights can be found. The relative height informs the locksmith of the size needed for the new key pins.
Once all grooves are measured (usually five) and the proper size key pins are gathered and placed in the correct holes, the key pin size is easily verified by checking to see that the pin is flush against the cylinder (what will become the shear line once the bible is refitted). The plug is reinserted into the bible, pushing out the follower, at a 90 degree angle.
If the plug is improperly reinserted the first driver pin may fall into the sixth chamber and premaritally lock the mechanism. The lock is put back into the knob after the c clip is reattached, and the shank and rose can be fitted back together.