An Overview of Cylindrical Locksets

Cylindrical locksets are the most common type of residential lockset in the United States.  This is due to both hardware costs and ease of installation.  This type of lockset came about in the 1930’s, but gained popularity in the 1950’s when Kwikset began producing a cylindrical lock that was much easier to install than those offered by its competitors.  The most common types of cylindrical locksets are key-in-knob locks, key-in-lever locks and cylindrical deadbolts.  Cylindrical locks are also common on commercial buildings, but are not seen on hollow aluminum doors due to their dimensions.

            A cylindrical lock is installed on a door by drilling a hole through both sides of the door for the lock assembly.  The location of this hole will vary depending on the lock’s backset.  Backset is the distance between the edge of the door and the center of the hole that is to be drilled for the lock assembly.  Some residential locksets feature an adjustable backset.  This allows the lock to be installed on a door that has already been drilled one of the two common backsets, which are 2 3/8” and 2 ¾”.  A second, smaller hole (usually 1” in diameter), is then drilled into the edge of the door until it intersects with the larger hole that has already been drilled.  A small mortise is then made for the latch faceplate using either a chisel or a router.  Some doors already come with these holes made.  These holes are known as a cross-bore.

Key-in-knob lock (bottom) and deadbolt (top) - View from unsecured side of door

            By contrast, it is much more difficult to produce a mortise pocket in the side of the door without the use of expensive specialized jigs and bits.  Most cylindrical locks, such as Kwikset knobs also allow a little more room for error than a mortise lock when it comes to the location of the holes drilled.  However, installation of either type of lock should only be done using a jig and never with the paper template that is often supplied with these locks—this template can easily become distorted when folded and if the door is beveled the holes on each side will be off.  A jig however allows both holes to line up in the same location and meet in the center of the door.

            The downside to cylindrical locksets is that they are generally less secure than mortise locks.  Also, excluding a few rare exceptions (e.g. Schlage G-Series) cylindrical deadbolts and key-in-knob locks are not interconnected.  This means that if you need to exit a room and the deadbolt is locked, you must rotate the inside thumb turn first and then rotate the inside handle in order to egress.  By contrast, most mortise locks today are interconnected allowing you to simply rotate the inside handle and open the door even if the deadbolt has been thrown.  For this reason cylindrical deadbolts are virtually nonexistent in commercial buildings.

            Ultimately, it comes down to cost versus quality.  Mortise locks are typically a better investment for a commercial building where doors see frequent usage, or the front door to a residence, where the owner wishes to preserve the original styling.  Also, if a door has already been fitted with a mortise lock, converting to a cylindrical lockset is generally not practical, as the entire mortise pocket has to be filled in as to prevent damage to the door that would otherwise result from the hollow cavity.  Therefore, if the mortise lock on an interior door to an older home starts to experience issues, it is advisable to either have it repaired, or track down a replacement lockset as opposed to running out to a big-box retailer and grabbing the first doorknob you see.

An Introduction to Mortise Locks

A mortise lock is a type of lockset that is installed by cutting a pocket into the side of a door.  Before mortise locks became widely available in the late nineteenth century, most door locks were surface mounted, and typically would consist of a cast iron box bolted to the inside of the door with a hole for the key to be inserted through.  This can be unsightly and many surface mounted locks were handed, meaning that you would have to specify the type of door you had when you purchased a lock.  Today surface mounted locks still exist in the form of some panic hardware and interlocking deadbolts.

This Sargent & Greenleaf lever tumbler lock is the oldest lock in my collection.  It was most likely produced in the late nineteenth century right here in Rochester

Then came mortise locks.  Installing the lockset inside a cavity in the door allowed for a more aesthetic appearance and provided better security against forcible entry.  Although some mortise locks were handed, the handing could usually be reversed by opening up the box and flipping the latch and spindle hub around (if it uses a swivel spindle).  On newer mortise locks, the handing can be reversed without even having to open up the box.  This made for a more secure and more versatile lockset.  Most mortise locks should be installed on doors that are at least 1 3/4" thick.

Mortise locks come in many shapes and sizes.  Some mortise locks accept a warded bit key.  Bit key mortise locks are common on the interior doors of many homes within the city of Rochester.  Mortise locks that use a cylinder key may be found on the exterior doors of some older homes.  Today most mortise locks are built to fit inside an ANSI Type 86 mortise pocket.  This is the standard pocket that is usually mortised into a door at the factory (if you're ordering a fire-labeled door it has to be mortised at the factory to retain its fire rating).  The customer may then install whatever brand of lock they prefer.  Originally different lock manufacturers produced mortise locks in different dimensions, so it may be difficult to find a replacement mortise lock for an older door.

Many mortise locks feature two buttons located on the faceplate either above or below the latch.  These buttons are called the stopworks.  Pushing one of these buttons will lock the outside knob or thumb piece.  Pushing the other button will unlock the outside knob or thumb piece.  The user may then use their key to retract the latch and enter, or they may exit by simply rotating the inside knob, which is always unlocked.

This Corbin mortise lock features both a latch and a deadbolt, which are unlocked by the same cylinder.  This lock is not interconnected, so the deadbolt must be retracted using the inside thumb turn before someone can get out.

Another advantage of many mortise locks is that the latch and deadbolt are usually contained in a single unit.  On many newer mortise locks, they are also interconnected.  This means that rotating the inside handle will retract both the deadbolt and the latch.  This is especially useful from a life-safety standpoint, as it allows a person to exit by only rotating the inside handle.  The person does not have to fumble with a thumb turn to retract a deadbolt and then twist the handle to get out.

Today mortise locks are less common, largely due to hardware and labor costs when compared to cylindrical locksets.  However in some commercial construction and applications requiring a robust lockset with longevity, mortise locks are still popular.  Ultimately it comes down to whether the customer is looking for reliability over time or a lockset that is more affordable and relatively easy to install by comparison.