Router
Also called: plunge router, electric router, router table, trim router
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A router is a handheld power tool that spins a cutting bit at high speed, letting a woodworker cut grooves, shape edges, and form joints in wood. Turned upside down and bolted beneath a table, with the bit poking up through a hole in its surface, the same tool becomes a stationary machine that the wood is fed across instead of being moved by hand.
Handheld or table-mounted
A handheld router is guided over the work by its own base plate, which rests flat on the surface while the bit does the cutting. Rogowski (2002) sets out a basic rule for working an outside edge this way: keep travelling in one direction, left to right as you go around the piece, and never twist the body of the tool part-way through a cut, since on some routers the base and the bit are not quite centred on each other, and any rotation would throw the cut line off. Turn the same tool upside down and clamp it beneath a table, and control shifts from the operator's hands to a fence and the table surface itself; Jigs and Fixtures (2004) treats this as the safer of the two setups for a workpiece that is small, narrow, or an awkward shape, since such a piece is easier to slide steadily across a fixed bit than to balance a handheld tool on top of it. The same source adds that, in a shop without a jointer, the machine normally used to true up an edge, a router table can be pressed into service to do that job instead.
Building or buying a table
Building a table from scratch starts with the router itself: Frid (1979) has the woodworker trace the bolt pattern off the underside of the tool's own base, transfer those points onto a sheet of plywood or Masonite and drill through, then cut a shallow recess into the underside of that sheet so the body of the router nests into it flush with the surface. Buying a ready-made top skips that work; Bird (2004) reports that such tops are inexpensive, machined to close tolerances on computer-controlled (CNC) equipment, and supplied with a slot already cut for a mitre gauge. Bird (2004) further recommends reserving the more powerful of two routers for permanent mounting in the table and keeping the lighter one free to carry around the shop.
Fences, cutting circle and feed direction
A fence, essentially a straight bar the wood is pressed against and slid along, is the usual way of controlling a cut on a router table; Rogowski (2002) treats it as standard equipment for guiding the work past the bit. Jigs and Fixtures (2004) supplies two working definitions for setting a fence correctly: what the spinning bit sweeps out at its widest is called the cutting circle, and the offset is simply how far back the fence sits from the near edge of that circle. Many router tables split the fence into two independently adjustable halves either side of the bit opening; set with the halves pulled outboard of the bit, Hylton (2005) observes that the resulting feed direction lines up with the direction stock is normally pushed across a table saw, a coincidence that suits anyone already used to that motion. Building the router table straight into the extension wing of a table saw trades on that overlap and saves floor space, though Hylton (2005) also flags the catch: a workpiece has to be lifted and repositioned every time work alternates between the saw and the router, which soon becomes tiresome.
What the bit shape allows
Bird (2004) makes a point about bit geometry that explains much of a router's versatility: ordinary bits such as straight bits and dovetail bits are ground to cut through their ends and not just their sides, so the tool is capable of grooves, dovetails, an interlocking joint formed from angled pins and sockets, and a handful of other simple joints that a spindle shaper, a different table-mounted cutter, is not built to produce. That end-cutting ability is also what lets a router work into a stopped mortise, a slot that does not run the full length of the piece, cleanly from above. Frid (1979) gives a practical rule for that operation: keep the tool travelling so the bit is always cutting away from the fence, never back toward it, or control of the cut is lost.