How A Number Lock Works?

Portable locks are probably one of the most widely used and trusted devices. Be it to lock a cupboard, a bike, a secret diary, a secret cabinet at home while you are away at college, and many more, it helps us protect our valuables and sleep tension-free. But what if you are forgetful, clumsy or maybe just a lazy person? The traditional padlock, and the dire difficulty of having to keep-safe, plan and carry a key every time,

is definitely laborious. And so, for all the scatter-brains, we have the number lock. All you have to do is remember a few digits and you no longer have to gruelingly carry a key.

Parts of a Number lock

After several unsuccessful attempts to open it at home, we got the number lock opened by a locksmith.

Combination locks have a (which metal body and a steel shackle, which is used to lock around things.The round bits with numbers on them are the dials. These are rotated to enter the correct combination which unlocks the shackle. There are 4 gears, one for each dial, which sit inside the dials. Gears wrap around the shackle, which is the innermost shaft. Additionally, there is a spring, and a metal plate

How it works?

The shackle has 5 ledges on it. 4 are for the gears, and the topmost one is to stop the shackle from sliding out of the lock. These prevent the shackle from sliding from sliding through the gears.

The gears have notches on the inside. When the notches of all the 4 gears are aligned with the ledges on the shackle, the ledges slide through the gears, opening the lock. If they are not aligned, the lock won't open. Thus, these notches and ledges are a gate mechanism. The gears in turn have pins on its outer surface. These fit the dials on the gear such that, when the number-dial is turned, the gear underneath also turns.

So here is how only one combination on the number-dial, which aligns the ledges on the shackle with the grooves on the gear, opens the number-lock. Cool, right?

But what makes it extraordinary is how the combination can be changed.

When the lock is in the open state, with the correct combination keyed in, all the gears are aligned with the inner shaft. To change the code, we rotate the shackle by 90 degrees, and push it in. keeping the shackle pressed in this position, we enter the combination, and voila, the code is changed.

Remember the 5th ledge on the shackle, which prevents the shackle from sliding out of the lock?

When we look closely at the outer casing, we notice that there are two notches around the hole for the shackle, which facilitate this turning motion and allow the topmost ledger to slide inside the casing. When the shaft is pushed, the shaft and the gears move down from its position, leaving the discs free to rotate. After the dials are rotated to enter the new combination, we release the shackle. A spring system at the bottom of the shackle facilitates the return of the shackle and the gears, such that once again the gears and the dials are locked, but now with a new combination.

What about the metal plate?

The cherry on the top!!

So what does the metal plate do?

After discussions, experiments and many trials, we figured this out. The grooves on the gear facilitate a small rotation of the shackle, even when the ledgers are aligned properly, in simpler terms, bigger grooves. The metal plate, when the outer casing is intact, behaves like 4 tiny springs (a ledge in the outer plate presses into the metal plate). This facilitates the easy rotation of the discs, and gives the rotation a step-like feature, i.e., only numbers and not the spaces between them can be keyed in. This increases the security and makes it difficult to crack the code.

Materials Used

Why was it difficult to break open?

The sturdy outer casing has 4 rivets in it and has pressed clinched joints, which is why it was almost impossible to break it open. The only way to open it is to drill out the rivets. The outer casing is usually cast out of an alloy of brass and steel, brass or steel. The shackles are made of steel for cut-resistance. The dials and gears are also cast from the same material as the outer casing. The metal plate is made from steel, and is quite flexible giving it spring like fe

Complexities in the mechanism

All the parts have a purpose. The additional half-grooves in the inside of the gear make it difficult to crack the code. A few parts can be eliminated, and a simpler mechanism can be used but then we won't be able to reset the combination. Using a metal plate instead of four tiny springs eliminates the need to make ledges and additional parts in the case to hold them in place.