Ever wondered how a Pinball game "tilts?"  Well, it's due to this really simple mechanism that employs the use of a "plumb bob."  For those of you that don't know what a plumb bob is, it is used in surveying and construction as a means to let gravity tell you where a line exists that is perfectly vertical.  The gravity of the Earth pulls the plumb bob towards the center of the earth and the string or metal rod connected to the plumb bob represents a perfect vertical line that is level (vertically level).  You will also find one or more weighted switches that are known as a "slam switch" rather than a tilt mechanism. Let's begin by looking at the tilting mechanism known as a "plumb bob" or "bob."

The Tilt Mechanism

In the case of a Pinball game, there's a small metal rod with a plumb bob attached to it by running the rod through the center of the plumb bob.  There are several ways to control how high or low the weight (bob) will be on the metal rod that will affect how sensitive the tilt mechanism is set.  Sometimes the rod is threaded and the bob is placed on the rod with a wing nut used under the bob to screw up and down to determine the bob's height. You may also see a "pinch clip" used around the metal rod to adjust the height of the bob on the rod.  And finally, some games have a bob that has a hole drilled in the side of it with a "set screw" that tightens on the rod to adjust the bob's height on the rod.

Take a look at the picture to the right to understand the components in a tilt mechanism.  You can see the vertical steel rod that hangs down through a brass plate with a hole in it, and at the end - a tapered weight (the "bob" of "plumb bob") with a "pinch clip" under it that determines where the bob is placed on the rod.  The "pinch clip" is used under the bob to keep it from not only falling off of the hanging rod, but to also adjust where the tapered part of the bob fits within the brass plate.

If you lower the bob on the rod by pinching the clip and letting the bob slide down the rod a little, it will be harder to tilt the game since the distance between the metal of the bob and the brass circular opening is larger.  If you pinch the clip and raise the bob upwards on the rod, more of the tapered part of the bob will be inside the brass plate so the distance between the bob and the brass ring is less. 

As you can see, the further up the rod the bob is placed, the less distance there is between the bob and the circular hole in the brass plate.  This means that if the bob is raised up rather high on the rod (but not touching the brass plate), and the game is jiggled even a little bit, the weighted rod will start swinging and the bob will eventually touch the brass ring which will instantly cause the game to register a tilt.

The picture to the left shows an older EM game and its tilt mechanism.  Once again, you can see the hanging rod passing through the center of a brass plate with a bob connected to the rod. In this example, the bob is held in position on the rod by using a set screw.  To adjust the bob's position, you loosen the set screw, then you raise or lower the bob to where you want it, then you tighten the set screw.  This picture doesn't show it very well, but the set screw can be tightened and loosened with just a finger and thumb.

Notice the two screws holding the brass plate to the side of the game box. Once a game is set up and leveled, these screws can be loosened to affect where the opening in the brass plate is centered.  You adjust the plate so that the circular opening has an equal distance from the bob as it hangs.  The screws are also used to set the plate somewhat level rather than slanted as this picture shows (the left side of the plate looks like it slants downwards).  This game was not set up in the proper position so the brass plate appears to slope downwards.

Tilt Mechanism Electrical Components

You can also see that two wires are contacting the plate behind the left screw in the picture above.  These wires are connected to the tilt part of the circuitry so that the game knows when the bob contacts the brass plate.  You can't see it in this picture, but the red wire in the picture above is connected to the metal that has the rod hanging down.  The result is that when the bob contacts the plate, the white wire and the red wire are connected through the rod, the bob, and the brass plate resulting in a closed circuit.

What Happens When You Tilt?

Tilting can have different outcomes such as the game is over on that ball and you don't get any outstanding points, or the whole game can end, the lights turn off, etc.  In newer Electronic games there can actually be a threshold for the number of times a person can cause a tilt.  On the newer games, many times the threshold is set at 3 times that you can get away with a tilt before the game actually tilts on the ball in play.  Ths gives a player a clue about how rough the game can be "nudged."  The older games didn't have the threshold setting capability and the result is pretty consistent when you tilt - you lose your turn on the ball in play and you won't get your accumulated bonus scores you have coming for that ball.

If you like a game you can practically jerk all over the place, then lower the plumb bob (some folks even take it off the metal rod).  For me, I don't care for people banging my games around, so I keep the tolerance fairly tight by raising the weight high on the rod.

What Is A Slam Switch?

The coin door, playfield, and game box slam switches use a common mechanism to indicate that someone is doing something destructive to the game. A weighted contact blade sways back and forth when the game is struck on the coin door (via a kick for example), or the game is lifted up and dropped on the floor, or someone bangs really hard on the playfield glass.  The weighted blade sways back and forth until it strikes the stationary blade and a slam tilt results. 

The picture on the left shows a coin door slam switch located on the backside of the coin door.  Kick the door and you lose a game for your effort.

The picture at the right shows a playfield slam switch as found on a Joker Poker.  This switch is set pretty loose to avoid accidental closure since it's a home game and shouldn't see any slamming going on.

Sometimes, as shown in the picture at the left of a Joker Poker tilt mechanism, there's a ball that rolls in a trough such that when the game is lifted up, the ball rolls to one end of the trough and it strikes a switch that either opens or closes ending the game in play.  You can also see yet another view of the switch for the ball to strike when the game is lifted, tilt set screw, brass plate, and the bob which in this case is mounted upside down. Haven't seen a bob mounted this way before, but it works the same way although it is more sensitive due to the bob being closer to the pivot point.

Chip Morton offered an explanation of why the bob may be mounted this way based on his experience in a bowling alley. He said that some of the kids would lift up the game under the coin door and then drop it on the floor with the intention of causing the bob to fall down or off the wire (most likely those that use a pinch wire or metal tensioner that fits over the end of the wire shaft, rather than a set screw). Imagine the bob slides all the way down the wire shaft it hangs from and then rests on the bottom of the game box (if a long enough wire). Obviously it won't be tilting anytime soon since it can no longer swing back and forth when the game is jostled.

Even if it doesn't slide all the way down and is just very low on the wire, it makes the tilt much less likely to happen. This allows the game to be shaken around a bit more to avoid tilts, but isn't what the operator probably wanted to have happen. By mounting the bob the way it is shown in the picture (upside down), when a person lifts up the cabinet and lets it slam down to force the bob down the wire, it is permanently tilted which means it won't accept coins nor be playable until the operator resets it. Just one more way to work around naughty players.

Well, there you have it!  Probably more than you ever wanted to know about a tilt mechanism or a slam switch, but now you know what the mechanism looks like and how it operates.  For all those players that are rough on games, hopefully you tilt!