A router is a woodworking tool used to rout out (hollow out) an area in the face of a piece of wood. It was a tool particularly used by pattern makers and staircase makers and consisted of a broad-based wooden hand plane with a narrow blade projecting well beyond its base plate gaining it the nickname Old Woman's Tooth. Since about 1960, it has been replaced by the modern spindle router, which was designed for the same work, although the first electric hand routers appeared in the years just after World War I. Further refinement produced the plunge router, invented by Elu (now part of DeWalt) in Germany in the late 1940s. This is even better adapted for many types of work. Today, traditional hand-powered routers are often called router planes. Modern routers are often used in place of traditional moulding planes or spindle moulder machines for edge decoration (moulding) of timber. Related to the router, is a smaller lighter version designed specifically for trimming laminates. It can be used for smaller general routing work. For example with an appropriate jig it can be used for recessing door hinges and recessing lock faceplates etc.
The tool usually consists of a base housing a vertically mounted universal electric motor with a collet on the end of its shaft. The bit is height-adjustable to allow protrusion through an opening in a flat sole plate, usually via adjusting the motor-mounting height (the mechanism of adjustment is widely varied among manufacturers). Control of the router is derived from a handle or knob on each side of the device, or by the more recently developed "D-handle".
There are two standard types of router — plunge and fixed. When using a plunge-base router, the sole of the base is placed on the face of the work with the cutting bit raised above the work, then the motor is turned on and the cutter is lowered into the work. With a fixed-base router, the cut depth is set before the tool is turned on. The sole plate is then either rested flat on the workpiece overhanging the edge so that the cutting bit is not contacting the work (and then entering the work from the side once the motor is turned on), or the sole plate is placed at an angle with the bit above the work and the bit is "rocked" over into the work once the motor is turned on. In each case, the bit cuts its way in, but the plunge router does it in a more refined way, although the bit used must be shaped so it bores into the wood when lowered.
The baseplate (sole plate) is generally circular (though this, too, varies by individual models) and may be used in conjunction with a fence attached to the base, which then braces the router against the edge of the work, or via a straightedge clamped across the work to obtain a straight cut. Other means of guiding the machine include the template guide bushing secured in the base around the router cutter, or router cutters with built-in guide bearings. Both of these run against a straight edge or shaped template. Without this, the varying reaction of the wood against the torque of the tool makes it impossible to control with the precision normally required.
A simple router table consists of a rigid top with the router bolted or screwed directly to the underside. More complex solutions can be developed to allow the router to be easily removed from the table, and there is a wide range of commercially available systems.
In this mode, the router can perform tasks similar to a spindle moulder. For smaller, lighter jobs, the router used in this way can be more convenient than the spindle moulder, with the task of set up being somewhat faster. There is also a much wider range of bit profiles available for the router, although the size is limited.
The router table is usually oriented so that the router bit is vertical and the table over which the work is passed is horizontal. Variations on this include the horizontal router table, in which the table remains horizontal but the router is mounted vertically above the table, so that the router bit cuts from the side. This is an alternative for edge operations, such as panel raising and slot cutting.
Router bits come in hundreds of varieties to create either decorative effects or joinery aids. Generally, they are classified as either high-speed steel (HSS) or carbide-tipped, however some recent innovations such as solid carbide bits provide even more variety for specialized tasks.
Aside from the materials they are made of, bits can be classified as edge bits or non-edge bits, and whether the bit is designed to be anti-kickback. Edge bits have a small wheel bearing to act as a fence against the work in making edge mouldings. Non-edge bits require the use of a fence, either on a router table or attached to the work or router. Anti-kickback bits employ added non-cutting bit material around the circumference of the bit's shoulders which serves to limit feed-rate. This reduces the chance that the workpiece is pushed too deeply into the bit (which would result in significant kickback from the cutting edge being unable to compensate).
Bits also differ by the diameter of their shank, with ½ inch, 12 mm, 10 mm, 3/8 inch, 8 mm and ¼ inch and 6 mm shanks (ordered from thickest to thinnest) being the most common. Half-inch bits cost more but, being stiffer, are less prone to vibration (giving smoother cuts) and are less likely to break than the smaller sizes. The bit shank and router collet sizes must match. Many routers come with removable collets for the popular shank sizes (in the USA 1/2in and 1/4in, in Great Britain 1/2in, 8 mm and 1/4in and metric sizes in Europe - although in the United States the 3/8-inch and 8 mm sizes are often only available for extra cost).
Many modern routers allow the speed of the bit's rotation to be varied. A slower rotation allows bits of larger cutting diameter to be used safely. Typical speeds range from 8,000 to 30,000 rpm.
Router Bits can be made to match any imaginable profile. Companies which manufacture custom router bits may be found on the Internet. This is especially beneficial for home restoration projects when often the trim and molding of the home is out of production.
A related tool, called a spindle moulder (UK) or shaper (North America), is used to hold larger cutter heads and can be used for deeper or larger-diameter cuts. Another related machine is the pin router, a larger static version of the hand electric router but normally with a much more powerful motor and other features such as automatic template copying.
Some profile cutters use a cutting head reminiscent of a spindle router. These should not be confused with profile cutters used for steel plate which use a flame as the cutting method.