Wooden combination lock
In terms of neat mechanical things to build out of wood, I figured a single dial sequential combination lock would be a neat thing to make. It would be relatively simple, involve movement, and also show people how a combination lock actually works.
I spent some time thinking about it, and the design I came up with was the simplest that would also be visually appealing that I could come up with. Unlike a real lock, my priority was to show how it actually works.
Like most real combination lock, such as a Dudley or master combination lock, the core
of the lock consists of three rotors. Each rotor has a notch in it, and when the three
notches are lined up, some sort of bar can drop into them, and allow the lock to be opened.
The front most rotor is directly coupled to the dial on the front of the lock.
All the rotors have tabs sticking out the front and back, so that once the front rotor
is turned by one turn, its tab hits the tab on the middle rotor. The middle rotor's tab
in turn sticks out the back, and can catch the tab in the rearmost rotor. So once
the middle rotor is turned one turn, the back most rotor is engaged also. So by turning
the dial two turns, the second and third rotors are caught with their tabs, and all three
rotors turn together.
Of course, the notches in the rotors are not aligned with each other at this point. To open the lock, one turns the dial to the right until the notch on the rear most rotor is aligned with the bar. The first number of the combination corresponds to the position that the dial needs to be turned to accomplish this.
After the first rotor is lined up, rotation is reversed. By turning counterclockwise
one turn, one will catch the middle rotor with the tab pushing it in the opposite
direction. Again, the rotor is turned until the notch on the second rotor lines up
with the bar.
After that, the rotation is again reversed, now turning clockwise again, until the
notch in the front most rotor is lined up with the bar. The picture at left shows
all three notches lined up, and the lock is ready to open.
This view shows the bar in the slots. The lock is constructed in such a way that the
bar getting into the slots actually turns the rotors a little bit.
This view with the back panel removed better illustrates how the lock opens.
The L-shaped part on the left turns clock wise to open the lock. This pulls the
bolt (on the bottom) back to the left at the same time.
The notches are not quite lined up in this shot. You can barely see the end of
the bar that needs to drop into the notches, and it's to the left of the notches.
The lock isn't actually functional without the back panel. The shaft that the rotors
sit on is part of the back panel, so this shot just has the rotors carefully
stacked in place where they would to, without their shaft, just to illustrate.
And here's the lock disassembled, showing all of its parts. Really, there is not very
much to it. Note that the shaft that the rotots turn on is glued into the back
piece of the plywood. This shaft doesn't turn. The rootors are semi-loose on this shaft,
and the spacers ideally would go on with a fair bit of friction.
The most complicated part is the part with the bar that drops into the notches, and that part is really only as complicated as it is because I wanted the workings of the lock to be very visible. On a real lock, the corresponding part would be much simpler.
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You can also Buy detailed plans for this combination lock |
| Demonstrating the wooden lock and comparing to regular padlocks | |
| And here's a video demonstration of the lock, and comparing it to some actual combination locks. I also found an interesting vulnerability of master lock padlocks, which I point out at the end of the video. | |
| The left-right-left combination lock trick | |
| There's no reason a combination lock has to be opened turning right left right. Really, any set of rotations that lines up the rotors will do. This video demonstrates opening a lock by turning left-right-left, although that involves dialing the lock to a different set of numbers than the regular right-left-right combination. | |
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You can also Buy detailed plans for this combination lock |
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