Impressioning

Impressioning

Impressioning is a non-destructive, covert method of creating a working key for a lock without picking or disassembly.

The process for impressioning wafer locks an pin tumbler locks is a pretty simple concept. Firs, the proper key blank for the lock is identified. This key blank is then put all the way into the lock, bound by applying turning pressure, and then moved. The movement causes the tumblers (which are being bound) to leave small marks on the key blank. These marks are then interpreted and filed. This process is repeated until a working key is made.

Blank Selection

Key blank selection is of vital importance to the whole impressioning process. Typical problems include selecting a blank which is too long, which can be detected by close inspection of the shoulder of the key blank. It should come in complete contact with the face of the plug (and sometimes recessed a little further into the plug). Another common problem is selecting a key blank which is too short, and does not pick up all the pins or wafers. A good example is selecting a SC1 blank versus an SC4 blank. SC1 and SC4 refer to a common industry reference, not manufacturer blank numbers. SC1 is a Schlage "C" keyway, five pin, and SC4 is the same keyway but for six pin. A six pin blank will rarely work in a five pin lock, the rare exception being if the tip of the blank happens to raise the sixth pin to the correct height.

Blank Preparation

For pin tumbler locks, the blank is usually prepared by using a fine file to clean the top edge of the blank to leave it with a uniform texture. This is also sometimes the case with wafer locks as well, but another method which many employ with great success on wafer locks is to file the side of the blank to leave it with a blade-like edge. Personal preference plays a great deal into blank preparation.

Sometimes other parts of the key blank are modified as well in preparation for impressioning. For example, M1 blanks for standard Master Locks sometimes have a shoulder which is too tall for impressioning due to the 'slop' in the lock. Without removing some of the top of the shoulder, it will 'bottom out' on the face of the lock before it actually allows the pins to bind.

Obtaining Marks

After the blank is selected and prepped, it is typically inserted into some kind of vice. Many companies offer locksmiths vices specifically for impressioning, but others rely simply on a pair of four inch vice grips. The key is then inserted into the lock. There are several different ways to obtain marks:

Pull-out method

The blank is inserted, and then turning pressure is applied. By withdrawing the key while applying pressure, sometimes small lines can be seen. Some specialty tools are made specifically for this, which have a trigger to pull the key out slightly.

Rocking method

The blank is inserted, and then turning pressure is applied. The key is the rocked up, against the pins, to obtain marks. Sometimes the key is tipped before applying turning pressure to isolate marks. For example, if the key is tipped with the tip upward, and then rocked so the head goes up, the marks closer to the head will be easier to identify. The opposite is also true, where the tip starts down and is rocked up. In that case, the tip will show more marks if there are any.

Bumping method

The blank is inserted, and turning pressure is applied. A strike is then applied to the head of the key from a small mallet for example. This strike against the binding pins leaves marks.

Interpreting Marks

After obtaining marks, the key is taken out of the lock for inspection. Sometimes aids are used, such as magnifying glasses or even different color lights. In pin tumbler locks, pins leave small circular marks. They will be a uniform distance from the edge of the blade (although not always centered), and from each other. In contrast, wafer locks tend to leave more rectangular marks, and they are very often found on the edge of the blade. It is for this reason that sometimes blanks are "knife edged" in preparation for impressioning, because wafer locks will 'crush' the knife edge away and leave very obvious marks.

Filing Marks

When a mark is identified, the next step is to file that cut. Some chose to use a code machine to cut the key down to the next possible known depth in that space, but others (or those lacking the equipment, will use a fine file. Very little is taken off at one time, depending on the particular lock. For example, Schlage locks (and many other locks) use ten different depths, so not much will be taken off. In contrast, some wafer locks (such as many of those in cars) have only four or five depths, in which case a little more may be taken away. Special care is given to the width and slope of cuts, as to not interfere with nearby marks and also allow for easy insertion and withdrawal of the key. If the slopes on a cut are too steep, the key may not enter or may get stuck in the lock.

Final Steps

When a pin reaches the correct height, it will no longer bind against the plug when turned, and will therefore no longer leave marks in that spot. Once all the pins are at the correct height, the plug will turn.

At this point, the key can be cleaned up by more carefully sloping edges, and taking off any sharp points. Sometimes a micrometer will be taken to the key and cuts will be rounded to the nearest known factory cut to produce a key by code.

Keys which have been used in impressioning are typically not used long, because they become exceptionally weak from being bound in the cylinder repeatedly.