When lumber is freshly cut at a sawmill, it’s not smooth; rather, it shows the marks from the saws used to cut it. What we buy in the lumberyard is not lumber that’s just been cut, but lumber that’s sanded-four-sides (SFS) to smooth it. That's why a one inch thick board is only 3/4 of an inch thick. The rest of the thickness has been taken away in the act of smoothing the board.
Actually, the board isn't sanded even though it is said to be sanded; it is planed. In olden times, planing a board took considerable amount of time with the use of a manual plane to get it flat and smooth. Today, manual planes are rarely used and this work is done by a power plane.
In addition to being used to smooth a recently cut board, planers are also used to change the thickness of the board. If 1/2" thick material is needed, it is easier to plane a standard 3/4" thick board down than it is to resaw and then plane. Of course, this is more wasteful as well, but few people need wood that is 1/8" thick.
Power planes generally have a series of blades (typically from one to three), mounted around a drum. The positioning of these blades is critical, both in comparison to one another and to the drum itself. If the blades aren't set at a consistent height, the surface of the board will be wavy. If they aren't installed level, they will cut more off of one side than the other and make the thickness of the board uneven.
A gauge is used for installing the blades to ensure consistency of their location. Even so, it’s necessary that extreme care is taken to ensure proper use of the gauge and blade alignment.
Planes operate at extremely high speed so that the scalloping of the surface of the board is minimized. The larger the drum and the faster it is moving, the less scalloping there will be. There will always be some scalloping with a power planer, although it can be minimized by using the planer slowly rather than forcing it to cut as quickly as possible.
Types of Power Planers
There are three basic types of power planers on the market, with a forth tool that falls into the category of being similar to a planer.
Benchtop Planers
There really is no such thing as a free-standing planer although benchtop planers can be mounted on a stand and used as if they were free-standing. The benchtop planer usually has a 12" wide drum, allowing it to be used for all sized boards. Since standard lumber is not sold over 12 inches wide (actually 11-1/2" wide) a benchtop planer will be able to be used for all wood. Benchtop planers are normally used in cabinet and furniture making.
Corded Planers
Corded and cordless planers are generally 3-1/2" wide, although there are a few models on the market which are 4-1/2" and even 6" wide. These are used mostly by carpenters for adjusting the size of a door, beveling the edges of doors and trimming boards in finish carpentry. They are also used by some hardwood floor installers, although it is much more common to use a floor sander.
Cordless Planers
Like all other handheld power tools, handheld planers are also available in cordless models. Since most uses that a carpenter has for a plane are for trimming boards, a cordless planer is much more convenient than having to connect an extension cord for making one cut. However, in applications where a lot of planing is needed, such as hardwood floors or butcher block counter tops, a cordless planer is not practical.
Jointers
Jointers are not technically planers and we have not included them in this category. The only reason I mention them is that they are similar in function. However, the main use of jointers is for edges of boards, whereas planers are used for the surface. When joining a number of boards together, such as for making a table top, the edges of the boards are usually run through a jointer, to ensure that they are straight, flat and smooth.
Things to Look for in a Planer
Planer Capacity
When shopping for a planer, the first thing you want to consider is the planer's capacity. This must match the type of work you are going to use it for. Buying a portable planer for use in furniture making is not practical, as you can't plane the full width of a board with it. Trying to use a benchtop planer for adjusting the width of a door won't work either, as you can't fit the door in it.
Motor Power
The amount of power that the motor provides is an important factor, as a more powerful motor will allow you to take thicker cuts with the tool. This is especially important when working with dense hardwoods, such as oak or maple.
Blades
Other than that, the most important part of any planer is the blade or blades. The more blades they have, the smoother a cut they will provide. Blade geometry is important as well, as a spiral cut will make for smoother finish.
Shoe/Fence
The shoe and fence of any planer must be made of durable cast metal, and be ground very smooth. Otherwise they will cause problems with catching the wood and making imperfections in the finish. If the plane has a tilting fence, it can be used quite well for making chamfered edges. Without a fence, you would have to make that as a freehand cut, which would probably end up uneven.
Depth Adjustment
All planers have a depth adjustment on them. The ease of use and accuracy of this adjustment is important for ensuring that the work comes out as intended. The depth adjustment must lock in place, to prevent it from migrating during the cut.