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This page covers the mechanical and electrical problems that can arise with domestic paper shredders.

Summary

Paper shredders are simple electromechanical devices but a fairly powerful motor is required to operate the shredding mechanism, and that power can break things internally.Problems can be divided into mechanical and electrical, but your first task might be to determine which it is in your particular case.

Safety

Always unplug before opening the device.

Keep fingers, hair and loose clothing well away from the mechanism.

Principles of operation

There are two types of shredder: strip-cut and cross-cut. Strip-cut shredders simply cut the paper into narrow strips which, with patience, could be reassembled. Cross-cut shredders are considerably more secure as these chop each strip into many short sections.

The shredding action is accomplished by two interlocking sets of circular cutterrs which rotate in oposit directions. The paper is drawn in between them so cutting into strips. In a cross-cut shredder, the circular cutters also have spikes which break up each strip.

The cutters are driven by a fairly powerful motor (always an AC/DC motor) through a gear chain to reduce the speed and increase the torque. A switch controls power to the motor. This is normally a 3 position switch with off, forward and reverse positions. The reverse position can be used in the case of a jam, to feed the paper back out again. In this position, the connections to the field winding of the electric motor (or to the brushes) are reversed, causing it to run backwards.

A mechanical or optical sesnsor detect when a piece of paper is inserted into the feed slot, only allowing the motor to run when this happens.

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