The insides of this lock are pretty ugly. When the gate is open the insides of the lock are exposed so you can see how they work. When closed there is a steel plate that covers the back. This is a warded lever tumbler lock.

The key for this lock is rather large. However, the shank could have been much shorter and the bow (handle) much smaller. If you make big "castle" locks for a customer that is going to use on dwelling doors you should probably provide a lighter weight key perhaps made of aluminum for daily use on a key chain. It would make a fancy "fob".

Lock making open up other areas of hardware to supply. This are replacement drawer pull plates and matching lock plate made for an 18th century dower chest. The original pull plates had all the little tabs that stick out broken off and heart lock plate was missing. Its shape was determined from the bleaching of the wood.

The part of the lock that slides and engages the strike plate is the "bolt". The bolt is moved directly or indirectly by the key which is a rotating lever. The key engages a notch in the bolt as it is rotated moving the bolt.

To design and build a lock you need to make a little layout like this. The closer the bolt is to the key the farther the bolt moves and the deeper the notch in the bolt needs to be. The notch is symmetrical so that the key can engage the notch and push the bolt from both directions.

IF the bolt should move out of position due to vibration or someone "trying" the door, it is possible for the bolt to move a small amount. As shown in figure 10 this can prevent the lock from being operated in either direction.

To prevent the problem above the notch should have a gentle curve at the bottom. When the key passed the curve there is significant clearance. If the bolt should slide back a little the key can push it out of the way easily.

Bolts have a friction spring, sometimes with a "detent" to hold it in proper position. However, you always need to allow for wear and tolerances.

The bolt notch can also be a shallow square cut with rounded corners. This reduces the throw of the bolt a little but may have other design advantages. In any case, you need to make a scale layout using a compass and ruler. For small locks you may want to make an oversized layout say 2 or 4 times size to be easier to draw.

The parts of a key are the bow (handle), shank, shoulder, throat and bit. The shoulder is optional depending on the type of key. Most barrel keys do not need a shoulder but may have one for decorative purposes. Modern bit keys that work from both sides of a lock need a shoulder to position the bit in the lock.

Modern bit keys have a "post" to help steady the key and a shoulder to position it. It may have ward cuts but it will always have tumbler cuts except on the cheapest of cabinet locks. The tumbler cuts are different heights as each tumbler must be raised a certain height to operate the lock. The tumbler and ward cuts are symmetrical on keys that operate from both sides of a lock

Keys with hollow ends are called "barrel" or drill keys. The hole fits over a pin in the lock. The pin acts as an obstruction to picking tools and a guide to keep the key centered.

The ward cuts must clear obstructions in the lock. Wards are usually circular and the key must clear them during most of its rotation. Making the wards is much more difficult than making the key to fit.

Like my "castle key" locks and keys can use both warding and lever tumblers for security.

Wards also consist of obstructions to putting the key in the lock. Slots were often cut in keys just as they are today to fit around tabs in the ward plates and the lock's escutcheon plate. Keys also had various protrusions to prevent them from fitting in the wrong lock. The same lock could be made that had a ward on the right and another on the left. A key that could get past both was a "master" key.

If you are making sets of locks and keys to multiple doors or gates then you may need to consider your designs carefully so that keys only fit their one lock BUT the master key fits all.

Medieval and Renaissance locks and keys were veritable mazes of complex wards. The cuts in the keys being very fine and made with a jeweler's saw. However, the security of a warded lock was so low that during this time locksmiths created many locks that used trickery such as valve and hidden keyholes as well as booby traps that would cut the fingers off a would be lock picker!

Locks of this period were often great works of art and less security devices.

Double bolts are actually a single bolt as shown. Make your layout carefully to be sure there is room for all the parts.

The spring adds friction to the bolt so it does not jiggle out of position OR is thrown out by a swinging door. The bolt may want a slight depression at each stopping point for the spring to engage into so that it stays in place.

Lever tumbler locks do not need a spring or detents as the tumblers hold the bolt securely in both end positions.

Two directional bolts generally use simple lever mechanisms. However from this point onwards locks can have gears, racks and all sorts of mechanical devices that we are not going to get into.

Another common lock made by smiths is the spring or "bear claw" lock. These are used on boxes, trunks and cabinets where you want the lid or door to automatically lock when closed. A simple leaf spring holds the bolt in position. The key just pushes the bolt to one side.

These type locks can be warded and or have lever tumblers.