Beginning locksmiths can encounter problems when keying commercial lock cylinders. Some problems can be caused by pin stacks, crushed springs, mis-cut keys, and assembly errors. A great deal of frustration can be eliminated by taking a close look at what is going on inside the cylinder and implementing the tips within this article.
Beginning locksmiths should never be shy about asking their more experience peers for solutions. Lock representatives are always willing to help out and often can provide materials that can aid in understanding what goes on inside the lock cylinder.
The definition of the pin stack is the overall height of all pin tumblers in a given chamber. The pin stack height is often expressed in units of increments established by the lock manufacturer. The pin stack height can be a given number or an actual size.
Interchangeable core manufacturers have given their cores a set pin stack height to ensure that the core operates properly when an operating key is inserted. One of the reasons for having a specific pin stack height is because the core is smaller than a standard lock cylinder and the operating space within the core is limited. A set pin stack height ensures that driver springs will not be crushed.
Pin stacks of most standard lock cylinders can be less critical as there is more space for springs to operate; therefore pin stacks do not have to be exact.
Locksmiths may forget to remove all pins and springs from the lock cylinder in preparation to rekey it. All the bottom pins and some master pins are removed by running a follower through the lock cylinder. Depending on the combination of the operating key, some master pins may remain in the upper chambers.
Master pins left behind will add to the overall height of the pin stack and could damage driver springs. Top pins might be too long for the pin stack, also creating a condition where the driver springs will be crushed. Driver springs left inside the lock cylinder shell could already be damaged.
Sometimes lock manufacturers create a problem when lock cylinders are delivered to locksmiths with the wrong size top pins installed. Zero-bitted or one-bitted (where a key cut with all zeroes or ones can operate the cylinder) lock cylinders, keyed from the factory, will often have short drivers installed, anticipating that the locksmith will not empty out the top pins when preparing for a rekey. This creates a problem during construction if the lock cylinder is turned without a blank construction key. Because short drivers were installed with short bottom pins, the pin stack at rest falls below the operating shear line. A turn with a screw driver may operate the lock but also may mangle the driver springs.
In Figure 01, during the keying process the top chambers were not emptied; a master pin was left in the third chamber and the top pin in the fourth chamber is too long for the new pin stack. A blank key inserted into this lock cylinder will crush the driver spring in the fourth chamber. Operating keys will be hard to insert. The extra master pin develops an unexpected operating shear line.
Driver springs have a load range. The “universal” driver springs found in popular pinning kits can safely compress about .315”. Compressions greater than .315” will crush or deform the driver spring so that it becomes ineffective.
The driver spring is placed on top of the pin stack to exert pressure on the pin tumblers.
To check that driver springs are in good shape, unload all pins, flip over the lock cylinder shell (so it is upside-down) and carefully remove the follower. Look into the bible portion of the shell; all pins should protrude from each chamber of the bible about .030”, like in Figure 03. If a visual check reveals that some driver springs do not protrude, like in Figure 04, those driver springs are crushed and must be replaced.
The definition of a bible is that portion of the cylinder shell normally houses the pin chambers.
The top pin or driver pin is the first pin in the stack that the driver spring directly contacts.
If a manufacturer does not specify an exact pin stack height, the pin stack height will be established as a range. For their standard commercial cylinders, Schlage uses three different top pins: T1 (.235”); T2 (.200”); and T3 (.165”). Figure 05 shows which top pins are designated for use with different pin stack heights. Notice that the pin stack heights fall into a range between .400” and .465”. What is inferred is that pin stack heights must be taller than .400” and shorter than .465”.
The definition of a uniform pin stack is an exact pin stack height established by the lock manufacturer.
The definition of an increment is the uniform difference between successive key cuts. It can be expressed as a dimension or a number designating the dimension.
The definition of a graduated driver set is a set of top pins of different lengths. Each length corresponds to the height of the rest of the pin stack to achieve a uniform pin stack. Usually the difference between pins in the set is a single increment.
There are advantages to having shorter (.400”) pin stacks. Driver springs are never fully compressed so they are never stressed or crushed; less compression translates to less overall pressure. Keys and plugs are less likely to wear out; and keys are easier to insert and remove.
Take Our Masterkeying Quiz (See bottom for answers) 1. The pin stack is: A. The sum of the heights of the bottom pin and all master pins in a chamber. B. Another name...