Lexicon DIY-Knowledge

Cordless screwdrivers


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cordless screwdrivers are mainly used as single-purpose machines for industrial purposes. The special version of the housing-grip screwdriver is also applied in the DIY sector.
Cordless screwdrivers have stepped transmissions which prefer high torques at low speeds. For the purpose of torque limitation a ratchet clutch is used which is adjustable in steps and disengages audibly when the chosen torque is reached.
The torque adjustment range is usually between 0.5...15 Nm. The maximum motor torque is 2...3 times higher than the maximum torque setting of the ratchet clutch.
This ensures that the delivered torque remains constant at the pre-set value when the actually available motor torque diminishes due to the reduced battery voltage towards the end of the battery discharge. The excess torque of the motor is used as a ?power reserve?, so-to-speak.
A special version of the cordless screwdriver, the so-called depth-stop screwdriver, is equipped with a depth stop. The depth stop has the effect that the screwdriving process is stopped by a disengaging clutch when a certain screw depth (e.g. of countersunk screws in wood) is reached.
Typical construction types of cordless screwdrivers are the versions with a pistol grip, a centre grip and, in the lower performance range, a housing grip.
(See also: IXO)