Contrary to what one might think upon hearing the term, key impressioning does not have anything to do with silly putty, molds, or plaster of paris. Instead, you start with a key blank and use the following method to arrive at a functioning key for a lock.
- Tools required
- Proper key blank that will fit the lock
- Vise-grip pliers
- Rat tail and pippin files (Swiss cut #4 variety)
- Skilled eyes
Clipping the vice grips on the key blank, you take your file and polish the top of the key (the part of the key that the pins come into contact with your pins. (Before starting the impressioning, it is generally good to count the number of pins in the lock with a hook pick, thus helping choose the correct sized blank.) You put the key into the keyhole using the vice grips, and gently turn it thus binding the key, then you jiggle the key up and down. You pull the key blank out and look at it. Initially you are looking for the perpendicular scrapes that the pins of the lock will have left on the key. File a few thousandths of brass off the key with your pippen or rat tail file (usually 4 total swipes of the file).
You repeat this process. Be very careful to only file if you see a little dimple in the key grooves that you are starting to file on the key. When you have filed enough material from the blank, you will have approximated the cut of the appropriate key and the lock should open when the key is turned.
This method is exceptionally good because high-security drivers (if they are grooved or mushroomed) are made irrelevant. This method works fantastically well on car doors and other wafer locks. To impression wafer locks, you should sharpen both sides of the key (only if the key is two sided); then the wafers will slice a nice little groove into your key.
This process could take 15 - 75 minutes based on 1) the skill of the locksmith and 2) the difficulty of the lock.
Please note, this method is more time consuming and difficult on locks with sidebars (e.g., Medeco, mul-t-lock, GM cars)