Tonight I digged up a tubular lock again and wanted to find out why it's so hard to pick it pin-by-pin...
Here's the lock:
It's a no-name cheap 7-pin tubular cam lock.
The long screw on the right was of course not part of the original lock, there was a brass pin flush with the lock, which I had to drill out to open the lock. The screw just replaces that pin.
On the top right hand side, you can see the inner parts of the lock:
The parts you can see are:
1) The core (the "shiny" chrome plated part). It's the longest part, it goes from the left (front of the lock) all the way to the right (back of the lock)
2) The "front" pins that stick out of the core to the left
3) The inner housing (it goes around the middle part of the core, and it can be fixed to the outer housing with the pin or screw mentioned above)
As you can already see, the parts of the pins that stick out correspond exactly to the key cuttings. While you can't SEE this when the core is mounted inside the housing, you can potentially FEEL it, or at least tools can use the effect - longer pins have more pressure from the springs. That's a major weakness of this lock and it's the reason why the various impressioning methods (tubular picks, plastic pens, toilet paper rolls, and so on) work.
Here is a picture where the core and the inner housing are separated:
The "front" pins are still sticking out of the core, and you can now see the "back" pins sticking out of the inner housing. All the "back" pins are the same.
Were they of different lengths, matching to the front pins, to make the total length of each pinstack the same, then decoding and impressioning would be much more difficult.
I believe that more expensive tubular locks have that feature, along with different springs as well.
However, the "back" pins are rounded at their front. That's one of the reasons why single-pin-picking is so difficult: They simply won't set. When applying torque, you can push a "front" pin until it reaches the shear line. It will stop there, so that you could decode the length, but it will not STAY there, because the "back" pin will not hold at the shear line, because of its round head...
I think the effect is a little bit different from that on illusion's lock in this thread:
viewtopic.php?t=11134
Here is a picture of the pins:
Please NOTE that I made a MISTAKE when placing the pins for this picture:
I placed all of the "front" pins the wrong way around.
The effect is this: As you can see they are serrated, all of them have 1 or even 2 thin cuts around them. However, these cuts do not block at the shear line, as the picture would indicate, but on the front side of the plug. Not sure why the manufacturer chose this option, and I'm not sure if it was maybe just a mistake.
And now the cutaway:
It's not very nice, but effective.
These are the plug and the inner housing, both cut with a Dremel cut-off wheel:
And this is the lock, with "windows", so I can see the pins at the shear line:
Hope you still like it
Cheers,
mh
