Electric screwdriver (cordless)
When cordless electric screwdrivers first came onto the market in the UK, they were the last power tool that a 'serious' diy'er wanted to be seen with - it was considered a weakness. But nowadays it is probably the first power tool that most people will buy as it takes out the monotonous work associated with inserting and removing screws.
Modern cordless electric screwdrivers save time and energy when fitting screws. They come in various shapes and sizes, can have a range interchangeable bits or even other tool attachments. The choice of cordless electric screwdrivers on the market is wide and it helps to know what to look for when thinking of purchasing one.
The shape determines how the tool is held, and this is often down to personal preference - however don't be too rigid in your choice, most people will get used to an unusual shape fairly quickly once they start using it.
The simplest cordless electric screwdrivers looks a bit like a traditional screwdriver, with the screwdriving bit extending from one end. Easy to use - being rigid and the body in line with the bit, it is very easy to locate the bit on the fixing and to tighten to a high torque.
A second shape are models which are hinged in the middle and are multi-positional with the screwdriver effectively converting between the straight form (above) and a pistol grip (below). The hinge (often lockable) allows various positions in between the two extremes so that the screwdriving bit can reach more restricted areas.
Another shape is the pistol grip style (very similar to some electric drills - in fact some tools can be used for both purposes). These tend to be bulkier that the former shapes meaning they may be less easy to access some areas.
Whichever style you are thinking of buying, check that the feel in your hand and make sure that it is comfortable and well balanced - this is especially important if you are left handed. Some models have rubberised or 'soft-grip' anti-slip handles which can make it easier to maintain a solid hold
The power of a cordless screwdriver is determined by the voltage of the battery pack - the higher the voltage of a model, the more powerful it will be. Typical the voltage for diy screwdrivers vary between 2.4 and 10.8 volts - anything below 3.6 volts may struggle with bigger screws or tougher materials.
The batteries are invariably rechargeable types and come with a charger, the batteries may be permanently built into the screwdriver or detachable from it - where the batteries are built in, the whole screwdriver normally fits into the charger (so the screwdriver is 'out of commission' while the batteries are being recharged), whereas the detachable batteries can be recharged on there own (so if you have two battery packs, you can carry on using the screwdriver while the other battery pack is being recharged).
Modern lithium ion battery technology (sometimes highlighted as a selling point) has reduced the size and weight of battery needed, so screwdrivers using it will be lighter and more compact. Lithium ion batteries also have the advantage that they hold their charge during storage - so if you only use the screwdriver occasionally, you shouldn't find the battery flat when you do come to use it.
Some screwdriver battery chargers include a 'fast charge' feature which enables the batteries to be recharged in a short period - typically an hour or less. This is useful if the screwdriver has built-in batteries or if the batteries have been allowed to run down.
Torque and torque control
The torque is the rotating force applied by the bit, as suggested above, the voltage of the screwdriver generally reflects the torque available - the higher the voltage, the higher the torque. Typically, different models can have maximum torque between 7 and 18 Nm (Newton Metres), not all models have the max torque specified.
Some screwdrivers do not provide any control over the torque being applied which can make their use problematic when working with some materials.
Other screwdrivers have some form of torque limiting adjustment, often in the form of an adjustable clutch which starts to slip at the pre-set torque. Often the adjustment just indicates a series of numbers (with low numbers being low torque, high numbers high torque), generally these just indicate different torques rather than specific levels of torque.
Having some form of torque limiting adjustment makes a screwdriver more versatile as it reduces the risk of overtightening and stripping threads especially important when working with softish materials.
Some electric screwdrivers have a single turning speed while others have selectable or fully variable speeds. Having different speeds available does provide greater control especially when working with small screws and/or you are starting off the screw without a pilot hole. The speeds will normally be shown as the No-Load Speed in RPM (revolutions per minute), the speed will reduce when driving a screw but the No-Load Speed gives a reasonably comparable guide. Typical speeds range from 200 to 600 rpm - if you will be using the screwdriver with very small screws, the lower the speed obtainable is generally the better.
Reverse/spindle lock action
All electric screwdrivers incorporate a selectable reverse action, which means that as well as inserting screws, the screwdriver can be used to remove them.
Often incorporated with the reverse control, a spindle lock will lock the bit mechanism so that the electric screwdriver can be used as a traditional screwdriver, this gives greater control when starting off or giving the final tightening to a screw. Manually using an electric screwdriver without a lock will rely on the friction of the gearbox to stop the bit from rotating - this not only puts undue force on the gearbox, it may not tighten the screw but just turn the gearbox/motor backwards.
Some screwdrivers incorporate a light beam along the line of the screwdriving bit - this can be useful if working in dark areas but check that the bulb is 'user replaceable', there's not a lot of point in having it if the first time you drop the screwdriver the bulb breaks and you cannot replace it.
LED lights tend to be more robust and less likely to fail.
Bits and drives
Most screwdrivers accept standard 6.35mm (¼ inch) hexagonal drive bits, choosing a screwdriver which uses 'non-standard' bits may restrict the number of bits and accessories which can be used with it. Some screwdrivers will directly accept only the small, single ended bits (25mm long) while others will only directly accept the longer, sometimes double ended, bits (about 50mm long). Generally the screwdrivers designed to take the longer bits are more versatile as extension pieces are available for these to accept the smaller bits - often accessory packs of bits will comprise a number of short bits, of different drives, plus the required extension piece. Extension pieces which incorporate a magnetic are very useful as they hold short bits in place.
The range of bits available and accessories is extremely wide, from various sizes of straight and pozidrive bits to Star and Hexagonal bits plus drive sockets.
Often the bits which come with a screwdriver are very limited, but additional ones are available either individually as required or as kits of varying types and sizes.