An experienced locksmith explains the working principle of mechanical combination locks – purely for discussion.

This method of opening safe (box) combination locks is fast and can open 100% of safe (box) combination locks, regardless of brand or type (three-disc or four-disc). It's simple and easy to learn; even someone who has never learned to open a safe before can learn within an hour and become a master at opening mechanical combination safes. I will now explain this opening method in detail below:

Some locksmiths specialize in the push-code technique for mechanical safes. Only after training and understanding the principles and internal structure of mechanical safes can an experienced locksmith repair mechanical safes and open them using the push-code method.

The working principle of a mechanical safe combination lock is based on a series of rotating discs inside the lock. The dial on the outside of the lock, when rotated sequentially left and right, aligns the notches on each disc. When the horizontal lever bolt on the latch is inserted into the notch, the bolt is pulled back, unlocking the lock. The markings on the dial indicate whether the notches on each disc are in the correct position. If the notches on the discs are not aligned, the combination lock will not open.

In the past, some experienced locksmiths could use their hearing to pinpoint the position of the notches on the dials within a mechanical safe's combination lock as they rotated, thus opening the lock. However, not every locksmith could do this, nor could they open every safe in this way; it largely depended on the quality of the safe's combination lock's manufacturing. Generally, locksmiths would use a small drill bit to create a small hole in the safe door and lock case. They would then insert a tiny surgical lamp into the hole, turn it on, and visually observe the movement of the notches on each dial as they rotated the dial. Alternatively, they could use a small steel wire to manipulate the dials, aligning the notches on all three dials at the nine o'clock position (in the direction of the lever bolt insertion). Another method was to use a puller to remove the dial, causing the dials to fall and freeing the lever bolt from jamming them. The basic principle of a safe's combination lock includes: dials, dial, latch hook, latch, cover, and drive wheel.

Currently, most mechanical combination safes in China use three dials, and almost all of them on the market have a 100-dial dial. Older safes have 90, 80, 70, and 60 dials. Newer safes often have false notches (false codes), some with three, some with five, and some with as many false notches as wheel teeth. The old method of trying to find the notches by twisting the handle is no longer effective. Sometimes the three dials are not the same size. If you try to eliminate false notches, you can only find one code on the dial and then push the code. This method is slow, and the opening rate is only about 60% to 70%. Now, many safes use screws and cotter pins to fix the dial.

Such safe (box) combination locks cannot be pulled out using a dial puller. For example, Yongfa safes have a special box that covers the dial, leaving only the notch where the lever bolt inserts into the dial exposed. Therefore, even if the dial is pulled out with a dial puller, the dial won't fall off; the lever bolt will still be stuck in the notch. If a locksmith, unfamiliar with the internal structure of a mechanical combination safe, uses a dial puller haphazardly, they might pull out the dial but still be unable to open the safe, causing many unnecessary problems.

In previous chapters, we mentioned using a power drill, so there's no need to repeat it here. Now, I will explain in detail the method and working principle of this quick method that can open mechanical safe (box) combination locks with a 100% success rate;

(Detailed Explanation of How to Open a Three-Plate Mechanical Safe (Box) with Combination Lock)

First, let's use a mechanical combination safe (box) with a dial of number 100 as a model. We'll divide the number 100 dial in half and start pushing the numbers from the middle, which is the 50th dial. The first step is to rotate the dial clockwise more than three times until the 50th dial is reached and stop, aligning it with the mark (the mark is at the 12 o'clock position). Then, rotate the dial counterclockwise one full turn until the 50th dial is reached. When we rotate counterclockwise 45 times, we will have a noticeable tactile feedback, feeling the contact between the driving points. That is, the driving and driven points of the first and second dials are in contact, and the two driving points occupy about five dials.

It's important to clarify here that the 50 mark is the number of the first disc we're assuming for positioning. When we rotate the disc counterclockwise to the 50 mark, we add the 45 mark. Why add the 45 mark? To clarify, we're searching for and assuming the mark of the second disc, which is commonly referred to as disc difference. More specifically, it's the distance between the point on the first disc and the point on the second disc that is less than the distance of a certain number of marks.

As discussed in previous chapters, it is necessary to repeat it here: the driving points of the stamped wheel discs are fixed, located at the 12 o'clock and 6 o'clock positions, with a distance of 50 marks between them. Subtracting the five marks occupied by the two driving points, we get 45 marks. Therefore, we need to add 45 marks.

At this point, we continue counterclockwise from the 50 mark to the 95 mark, then stop. Now, let's assume the two wheel discs are numbered (either 50, 49, 50, or 51). Before actually pushing the weight, tighten the handle and test the wheel disc notch and lever tolerance. Twist the disc left and right to see how much loosening occurs. Generally, it should loosen by about 3-5 marks; the maximum loosening is about 6 marks, and the minimum is about 4 marks.

The second disc is pre-positioned. For minor looseness, it's assumed to be at marks 94, 95, and 96. For significant looseness, it's assumed to be at marks 93, 94, 95, 96, and 97. For minor looseness, it's positioned at marks 94, 95, 96, and 97. Then, we can use our right hand to twist the handle to tighten it (twist it in the opening direction). We should loosen it slightly with our right hand, and after it passes the false opening, we should apply more force to twist the handle. The number on the third disc is determined through trial and error; it's not pre-positioned at any specific number. As long as the numbers on the first two discs are correct, it can enter the opening. For example...

50-93 50-94 50-95 50-96 50-97

49-93 49-94 49-95 49-96 49-97

51-93 51-94 51-95 51-96 51-97

52-93 52-94 52-95 52-96 52-97

48-93 48-94 48-95 48-96 48-97

It includes a total of 25 sets of combination numbers, from the first and second rounds. As long as the number is among these 25 sets of combination numbers, it will definitely be drawn.

If it fails to start this time, it usually takes no more than a minute, and those with quick eyes and hands can do it in just over twenty seconds.

If it doesn't work, start over. This time, assume the first dial's mark is 45. Then rotate the dial three full rotations clockwise to mark 45.

Reverse the dial one full turn to the 45 mark, then add another 45 mark and continue reversing and adding another 45 mark until you reach the 90 mark. Stop at this point. We can assume the first disc's positioning point is on marks 43, 44, 45, 46, and 47. The second disc's positioning point is then on marks 88, 89, 90, 91, and 92. This is the 25th combination of numbers.

43-88 43-89 43-90 43-91 43-92

44-88 44-89 44-90 44-91 44-92

45-88 45-89 45-90 45-91 45-92

46-88 46-89 46-90 46-91 46-92

47-88 47-89 47-90 47-91 47-92

If any one of these 25 combination numbers is correct, the machine will definitely open by turning the handle with the left hand while simultaneously rotating the dial clockwise with the right hand, following the method described above.

If that doesn't work, the next positioning is at mark 40. After spinning three full rotations clockwise, spin one full rotation counter-clockwise, repeating the same method. After reaching mark 40, add mark 45, making it mark 55. Let's assume the first wheel is positioned at marks 38, 39, 40, 41, and 42. The second wheel is positioned at marks 83, 84, 85, 86, and 87. These ten marks from the two wheels create 25 combinations. As long as the first and second wheels are on these 25 combinations, the game will definitely open. <I don't need to list all these combinations here.>

If it doesn't open this time, set the first disc's graduation number to 35 and operate as described above, rotating clockwise and counterclockwise, adding another 45 graduations. This time, let's assume the second disc's graduation number is 80. The first disc's graduations are 33, 34, 35, 36, and 37, and the second disc's graduations are 78, 79, 80, 81, and 82. These five graduations form twenty-five combinations. As long as the first and second discs fall within these twenty-five combinations, they can be opened.

If it doesn't open this time, next time set the first disc's scale to 30, and the second disc's scale to 75. This creates five scales for the first disc: 28, 29, 30, 31, and 32. The second disc will then have five scales: 73, 74, 75, 76, and 77. These create twenty-five combinations. Continue operating as before: rotate the discs and turn the handle. It will open if it's within one of these twenty-five combinations.

If these 25 sets of numbers still don't work, next time assume the first reel is positioned at mark 25 and the second reel at mark 70. The marks will then correspond to 23, 24, 25, 26, 27 on the first reel and 68, 69, 70, 71, 72 on the second reel. If these 25 sets of numbers still don't work, continue pushing down the number. Be sure to follow the method described above. It doesn't take long; if you're quick and have sharp eyes, it shouldn't take more than 5 minutes.

Continuing down, the first disc is at scale 20. The second disc is at scale 65. Next, the first disc is at scale 15, and the second disc is at scale 60. This continues down the first disc until scale 5, and the second disc down to scale 50.

If the wheel cannot be opened after pushing all the increments below 50, then the number must be above 50. In this case, we push it upwards. This time, we position the first wheel at increment 55. After rotating counterclockwise to increment 55, we add 45 increments to position the second wheel at increment 0. This creates a new set of twenty-five increments: 53, 54, 55, 56, 57 for the first wheel and 98, 99, 00, 1, 2 for the second wheel.

If the above method still fails to open the disc, then next time, let's assume the position is set at 60 on the first disc, and 05 on the second disc, and so on. Continue pushing down until the first disc reaches 0, and the second disc reaches 45. Repeat this process twenty times. These twenty times encompass 500 combinations of numbers. For an average person, this process takes about ten minutes; for a skilled and quick operator, it takes about eight minutes.

Within these 500 possible combinations, if you're lucky, you might be able to unlock the number in just 3 minutes without having to try so many times; if you're unlucky, you might have to try all of them before you can unlock it.

Even assuming none of these 500 combinations can open the safe's combination lock, we need to analyze the reasons. Why can't it be opened? Did we set the tolerance for the gap on the first disc too large? Or is it due to the disc difference between the first and second discs? Is the distance between the driving and driven points of the first and second discs, assumed to be 45 marks, inaccurate? Let's temporarily assume the disc difference is 40 marks and try pushing the code again. Again, rotate clockwise three times to mark 50, then counter-clockwise one time to mark 90. ​​Then use your right hand to turn the lever. This creates five disc numbers: 48, 49, 50, 51, 52. The five disc numbers are 88, 89, 90, 91, 92. These five marks form 25 combinations.

48-88 48-89 48-90 48-91 48-92

49-88 49-89 49-90 49-91 49-92

50-88 50-89 50-90 50-91 50-92

51-88 51-89 51-90 51-91 51-92

52-88 52-89 52-90 52-91 52-92

If any one of these twenty-five combination numbers is correct, the safe can be opened.

If we assume the first round of discs is set at 50 and start pushing down every five discs, until we reach the fifth disc, the disc should be 40 discs away from the mark. Starting from 90 and pushing forward to the 45th disc, there are 250 possible combinations. If you're lucky, you can open it; if you're unlucky, you can't.

Attention! The "luck" we're referring to is the luck of the person at the moment the combination lock is opened. Some people can open a safe in one or two minutes, while others may take tens of minutes or even an hour. This combination lock method is scientific and rigorous. It has been calculated by computer multiple times, conducted thousands of experiments, and successfully opened over a hundred brands of safes of various sizes and specifications in China. Therefore, we can be 100% certain that it can open the safe.

If the locksmith is experienced, they should be familiar with several brands of combination locks and have taken notes on the difference between the first and second dial plates for each brand. Is it 45? 40? 35? 50? Knowing the exact difference will make opening the lock much faster. This method of opening mechanical combination locks using push-codes is: science + patience + experience = success, plus luck = speed.

Getting back to the main point, let's continue explaining the working principle and operating procedure. After completing the downward movement, it starts to push upwards, dividing into five increments at a time, until the 95th increment, forming 250 new combination numbers. Among these 250 combination numbers, it's guaranteed to open. (Because we're using a 100-increase combination safe as an example, these safes were all produced after 2000, and the wheel discs are regular discs (stamped), with the driving and driven points at the 12 o'clock and 6 o'clock positions (slight deviations are acceptable).)