The picture on the above left shows the lock with all three cams. (Click on either picture to view it full size. Use your browser's back button to return.) The middle shaft has been removed from a back plate. It fits into the hole in the middle of the front cam. The deep notches are lined up under the pawl in the picture.

The shaft is D shaped. The cams have round holes, so they can rotate on the shaft. Between the cams, there are non-metallic spacers with D shaped holes. The spacers do not rotate on the shaft.

The middle and back cams have two pegs, one on each side. The front cam has one peg, on the back side of the cam. When the front cam is turned, its peg moves in a circular motion and, within one revolution, comes in contact with a peg on the middle cam. After it makes contact, it pushes the middle cam, so both turn. Within another revolution, the peg on the other side of the middle cam contacts a peg on the back cam, and starts pushing the back cam. Thus, within two revolutions of the lock dial, all three cams are turning.

When the first number of the combination is reached, the notch on the back cam is lined up under the pawl. The user reverses the direction of the dial (starts turning to the left.) The peg on the front cam pulls away from the peg on the middle cam. The spacers hold the middle and back cams in place by friction. A spring, not shown in the picture on the left, ensures that the cams are pressed against the spacers. (The picture on the right shows the back and middle cams, back plate, and spring.)

The user turns the dial one revolution to the left. The peg on the front cam contacts the peg on the middle cam and both cams start to turn. The other peg on the middle cam pulls away from the peg on the back cam. The back cam does not move, so its notch remains lined up under the pawl. When the user reaches the second number of the combination, the notch on the second cam lines up under the pawl. The user reverses the dial direction once more (starts turning to the right.) The peg on the front cam pulls away from the peg on the middle cam. Both the middle and back cams remain in place with their notches lined up under the pawl. When the third number of the combination is reached, the deep notch on the first cam lines up under the pawl. The shackle may be pulled, the latch assembly will rotate on its shaft, and the shackle will release from the lock.

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How the Combination Lock Works (cont.)