i. Types of imperfections
It is not possible to manufacture a “perfect lock”. Simply put, because the components within a lock need to move freely in order to operate, a lock manufacturer must allow tolerances for movement. If the outer diameter of a pin were exactly the same as the inner diameter of the chamber the pin would be a snug fit and would not move freely. The same is equally true of the plug in the shell. Since free movement is required, the lock manufacturer must allow for tolerances in the size of the components. Also, manufacturing to very tight tolerances is costly. This means that the lesser expensive models of locks will usually have far greater tolerances. This variation of size between components of the lock is the first type of imperfection that makes it possible to pick a lock.
Another is with respect to the location of the drilled chambers in the bible. There are actually several possible imperfections that can be produced in the manufacturing process. In many cases, the holes in the bible are “gang drilled”. This means that all the holes are drilled simultaneously with a specially made machine much like a drill press with several drill bits in a row. There are commonly 5 or 6 chambers in a typical North American cylinder. The chambers are drilled in a row parallel with the keyway. Since manufacturing processes are imperfect, this row of holes is often not perfectly parallel, leading to a situation described in illus. (blah). This misalignment of the pin chambers in the bible is one possible imperfection that we can exploit in lock picking.
It is possible in the manufacturing process to misalign the chambers in such a way that the holes are actually not even in a line. This is detailed in illus. (blah). This too can give the lock picker an opportunity to exploit these imperfections. How we do this will be discussed in the next chapter.
As you will see, the combination of tolerances in the size of components and misaligned chambers offers the lock picker all the opportunity needed to pick the lock. It is important to note that all locks suffer from one or more of these imperfections to varying degrees. As stated at the beginning of this chapter, it is not possible to manufacture a “perfect lock”.
ii. How lock picking works
Lock picking relies on exploiting the imperfections mentioned in the previous section. Since the components never fit perfectly, it is possible to cause driver pins to get stuck above the shear line while the key pins drop back down into the keyway. Once you are able to get all of the driver pins above the shear line there is nothing stopping the rotation of the plug and the lock will open. How we do this will be discussed in detail in the next chapter.