What is it?
A powered version of the classic woodworking hand tool. Electric planes will remove material quickly, easily, and in most cases leave a nice clean result. Ideal for finishing timber, dimensioning stock, and fettling the fit of all sorts of woodwork. A plane of some sort will feature as an "essential" tool in all but the most primitive of tool kits.
Most planes are based on the same type of technology, a rotating cutter block driven via a belt from a motor, that holds a pair of blades. This spins fast and typically takes 16,0000 cuts per minute out of the work. There is a fixed rear sole plate to guide the plane, and an adjustable front part to the sole plate that allows the depth of cut to be selected. Most electric planes can take cuts up to 1.5mm deep per pass, some of the more powerful ones may be able to do twice that (although lighter passes are usually to be preferred since a better finish will be obtained and there is more opportunity to correct mistakes before you go too far).
Whilst there are a ranges of sizes available, there is nothing like the huger range of subtle variations of size and design that you find with the traditional hand tool. Most planes aim to be a functional equivalent to a No.4 or Jack plane. Some are available with longer sole plates but these tend not to be as well suited to board jointing as a traditional No 7 plane. (for jointing and accurate dimensioning of stock the task usually falls to dedicated fixed machine tools such as the surface planer (Jointer) and the thicknesser).
Power planes are not well suited to very fine work since they don't have the same finesse as the traditional hand tools. So they won't completely replace the traditional tools in the hands of a fine furniture maker, but they will aid greatly with some tasks. They are also a bit big and heavy for some tasks, and not as flexible for jobs like cutting deep rebates.
They do score over the traditional tools in that they will cope better with man made boards such as MDF or chipboard, that are very unwilling to plane well with conventional tools. They are ideal for trimming 1mm off the bottom of all your kitchen unit plinths when you discover they only fitted correctly before you laid the flooring! (don't ask me how I know!)
Not the most dangerous of tools, but they do have the ability to bite if not treated with respect. The cutters are fast and sharp and will do a nice job of shredding fingers if you stick them in the wrong place (you have seen those adverts where someone chops a carrot in a food processor? Enough said!).
Ear defenders are a must, since planes are not only loud but concentrate a good deal of the noise into a narrow frequency band that will dull your hearing very quickly, and cause permanent damage with prolonged exposure.
Dust can be a serious hazard when planing some types of board, especially man made stuff like MDF. So a respirator is required some of the time. With more traditional woods the dust produced is more granular and less harmful.
Most planes use disposable TCT blades. These are usually reversible and if looked after should last a long time. Replacement sets start at about £5. The ease of blade adjustment and alignment is what separates some of the budget from the better quality tools however. Some are very fiddly to get set just right, while the better ones do it for you and get it right first time.
Bearing and cutter block quality will have a great effect on the finish achievable, your intended applications will however decide what level of product will produce acceptable results. Even the cheapest plane will quickly smooth rough timber and plane "down to a line", the quality of finish, the balance, the flexibility however will sort the ordinary from the good.
Vibration control is also important for both quality of results and operator fatigue.
Many planes eject shavings from a spout. Some make it easy to connect a vacuum hose to this, while some have odd shaped dust ports that require custom adaptors. Better planes also include dust collection bags built in.
Professional level tools will have motors rated for continuous use, while budget ones will have much shorter duty cycles. It is unwise to buy a tool based just on the amount of motor power and maximum depth of cut it can manage, since high power combined with deeps cuts is unlikely to give a satisfactory result unless the mechanics of the tool are also up to the job. When choosing a model it is worth reading the reviews since even the top end brands have some less well liked tools in this category.
Handy to have extras include fence attachments that enable to plane to be perfectly aligned in the horizontal axis - ideal for planing the edge of a door for example. Simple ones allow a right angle only, Better ones are adjustable to allow a variation in angle for applying a bevel to an edge. More elaborate accessories allow the plane to be mounted in a cage so that it can be used as a basic thicknessing machine (although with limited width of cut).
Relatively recently available these now offer freedom from the flex which is a big step forward for a plane. As usual expect to pay plenty for the option however. Currently the cordless tools seem restricted to the "pro" level brands so the usual warnings about poor batteries and chargers do not apply.
Second hand tools
Check that the unit runs smoothly. Make sure the cut is even and clean. Inspect the power lead for missing bits of insulation. If it is supposed to come with accessories lie fences, guide, dust port adaptors etc, then make sure you have them as they can be difficult to buy later for many of the lower end brands.