Basic Router Bits -- A Guide

Straight bits are probably the most widely-used router bits. They're used most often for cutting dadoes and rabbets, but are versatile enough to use in many other applications from mortising door hinges to cutting box joints. The bits come in a wide range of sizes, from about 1/8 inch up to over an inch wide. The most common size is probably a 3/4-inch bit, just right for a dado for nominal one-inch lumber. Special sizes are available for the sanded pine plywood that's 1/32 inch thinner than nominal (3/4 inch becomes 23/32, etc.)

Spiral bits are more expensive than fluted straight bits, but deliver a cleaner cut. Spirals are available in up-cut and down-cut designs; down-cut bits deliver a very clean edge but cut slowly and cannot make deep cuts in a single pass.

A rabbet is a groove cut so that it makes a "step" in the edge of a board. Routers alllow you to make the cut in one pass instead of the two it takes on a table saw.

Rabbet bits mount on an arbor - a spindle that fits into the router's chuck or collet, and has a nut and washer to hold the bit in place. The other part of the setup is a bearing that also mounts on the arbor: the bearing rolls along the edge of the board and keeps the depth of the cut constant. The width of the cut is controlled by a combination of the length of the "wings" on the bit and the diameter of the bearing.

A starter kit should have an arbor and two or more bearings of different sizes, plus a straight-sided rabbeting bit.

The chamfer bit allows you to cut a diagonal edge on a board, usually at a 45-degree angle, but other angles are also available. The geometric simplicity of the cut adds a finished look to the work. The chamfer bit also has a bearing at the tip to keep the line of the cut steady. The depth of the cut controls how wide the diagonal face will be.

A roundover bit creates a smooth, rounded edge on a board for a softer look. Roundover bits also have a bearing to control depth of cut.  The profile can either be a quarter circle or you can raise the bit slightly to cut a bullnose profile such as one might see on a stair tread.

A slot cutter bit is used to make narrow grooves, especially in the edges of boards. These grooves are used to join boards edge to edge or to create a space for a panel, such as in a cabinet door.

Slot cutters mount in an arbor like rabbet bits; the same arbor will most likely work for both. The width of the cutting teeth sets the width of the slot or groove cut by the bit. The combination of the slot cutter's diameter and the diameter of the bearing determines the depth of the slot.

A pair of slot cutters with a spacer between them is used to cut tongues on boards

After you've filled in your "library" of bits with the first five bits I've mentioned, you'll find yourself picking up specialty bits as the project demands them. If you do any work with veneers or laminates, you'll want a flush trim bit. The bearing on this bit is the same diameter as the bit, so it trims any overlapping veneer back to the edge of the board.

For fancy detail work, you may find yourself wanting a cove bit and / or an ogee bit. Cove bits cut the edge of wood in a concave rounded profile, the opposite of the convex rounded profile cut by the roundover bit. Ogee bits have both a rounded profile and a square shoulder, and are available in a variety of profiles to add detail to any edge.

A dovetail joint is both secure and attractive. Pair a dovetail bit with a dovetail jig to make this joint almost effortlessly.