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PRACTICAL EXAMPLE - ECCENTRIC CAM | |
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An eccentric cam is a disc with its centre of
rotation positioned ‘off centre’. This means as the cam rotates the flat
follower rises and falls at a constant rate. This type of cam is the
easiest to make and yet it is one of the most useful. |
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A mechanical toy based on a series of eccentric cams is seen below. As the handle is turned the shaft and the cams fixed to it rotate. Placed above the cams are a number of segments representing a ‘snake’. As the cams rotate some of the flat followers are pushed upwards whilst others drop down. This gives the impression that the snake is moving. |
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Below, the toy mechanism is using an offset circular cam profile (eccentric cam), means that alterations have to be made to the follower. The arm now rests on a ‘flat’ and the circular cam has been lowered. This cam gives a very smooth movement. This type of cam handles side forces really well. | |
QUESTION: 1. Design a toy or practical item based on a series of eccentric cams, working in a similar way as the ones seen above. |
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The eccentric cam below pushes the 'fish' upwards and allows it to drop downwards at a uniform speed. The overall speed is controlled by the speed the handle is turned. |
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ECCENTRIC CAM - T BOLT LOCKING SYSTEM | |
The T Bolt locking system shown below, is an excellent example of a eccentric cam at work. When the lever is vertical, the system is unlocked and material can be placed in position, or removed from under the drilling area. When the lever is pushed down to a horizontal position, the material is locked in place. It is now safe to drill. This locking system works because, the circular cam rotates ‘off centre’. Moving the lever into the horizontal position secures the material, by applying pressure, clamping it to the drill table. |
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