Whether you’re using a table mounted router to shape a curved drawer front or a handheld router to cut a groove, before you switch on the power, you’ll first need to determine how you’re going to guide the router through the intended path. There are four common ways to guide a router and it all depends upon the type of cut and the bit used to create the shape. In this article I’ll illustrate how I use guide bearings, bushings, the router baseplate, and the router table fence to make a wide variety of cuts.
Guide Bearings—Undoubtedly the most common method for guiding a router bit is the guide bearing. In fact, most of today’s router bits have a guide bearing to limit the cutting depth and keep the profile consistent (photo 1).
Profile bits, such as an ogee or corner rounding, have a guide bearing attached to the end of the bit which rolls along the unshaped portion of the stock (photo 2).
However, many bits, such as dovetail bits (photo 3), have a guide bearing on the shank while others, such as bits for shaping a mating tongue-and-groove, have a guide bearing between two cutters (photo 4).
Guide bearings can be used to follow a linear path or an intricate curve; the key to good results is a smooth surface for the guide bearing to follow. For example, when chamfering the corner of a curved chair leg, the guide bearing will roll irregularly along the rough surface from the bandsaw. Therefore, after bandsawing the curve of the leg, it’s important to smooth away the saw marks and provide a smooth rolling surface for the bearing.
By swapping out guide bearings on many bits you can change the cutting depth or even the profile. For example, when using a rabbeting bit (photo 5) it’s a good idea to have a few other guide bearings on hand; you can easily increase or decrease the cutting depth just by swapping out bearings.
When routing a rabbet in a difficult wood, such as curly cherry, I’ll start with a large diameter bearing to score the wood and prevent tearout. Afterwards, I’ll switch to the smaller bearing and complete the cut. In fact, if the rabbet is very deep I’ll sometimes use three different bearing diameters. The final pass with the smallest bearing leaves an incredibly smooth surface because even though the rabbet is deep, the actual cut is light. This technique is not limited to rabbeting bits; it works well for profile bits, too.
Corner rounding profile bits, can be made to shape a bead by switching to a smaller guide bearing (photo 6).
If you own a collection of various sizes of corning rounding bits then you also have beading bits of the same sizes. Just keep an assortment of guide bearings on hand. Amana offers a complete line of bearings from 1/4″ to 1-1/2” in diameter.
If you need to shape into a very small space then take a look at the Amana miniature bits (photo 7). These tiny bits each have a 3/16” diameter guide bearing and are available in several common decorative profiles as well as a rabbet and a flush trim.
Today many grooving bits, such as dovetail, core box and straight bits, are now available with a guide bearing on the shank (photo 8). They are often referred to as pattern bits because a template, or pattern, is positioned above the workpiece directly below the router (photo 9). Years ago this type of cut required a bushing attached to the baseplate. The bushing complicated the setup because the template had to be sized to account for the offset between the bit diameter and the bushing diameter. However, when creating a template for a pattern bit there is no need to calculate the offset because the bearing and bit share a common diameter. In other words, with a pattern bit the groove becomes the exact shape of the pattern. This simplifies the entire process.
Baseplate—If you’re routing grooves for shelves don’t overlook the economy and simplicity of guiding the router off of the baseplate (photo 10).
I’ll use this method often when routing the dovetailed sockets for drawer dividers in fine casework. When making a template for baseplate routing keep in mind that you’ll need to subtract the distance from the edge of the bit to the edge of the baseplate. Also, round router baseplates are not usually concentric to the router collet; if you rotate the router as you route the cut may be inconsistent. I simply mark a spot on the router baseplate with masking tape and keep it against the template as I route. If you use this method often you may want to solve this problem by replacing the round baseplate with one that is square (photo 11).
Additionally, when routing grooves off of the baseplate as long as the baseplate is against the template the groove will be straight. However, if the baseplate drifts away from the template the groove will meander. One solution is to make two templates and guide the router between them. However, with a bit of practice this isn’t a problem.
Bushings—(photo 12) A bushing is a metal sleeve that fits into the router baseplate; once it’s locked in place the bit slips through the bushing (photo 13).
With the plethora of pattern bits available I don’t use bushings as often as I once did. However, there are times when a bushing is still the only option; sometimes it’s necessary to cut a groove in a width for which a pattern bit is not available. Just keep in mind that the pattern will need to be sized to allow for the offset between the bushing and the bit (photo 14).
Fence—Router tables turn an ordinary router into a mini-shaper capable of performing many cuts that are out of the realm of a handheld router. When routing on a table, the fence limits the cut and rather than guiding the router, it guides the workpiece in a linear path. Even so, guide bearings still play a major role. Positioning the fence tangent to the guide bearing takes the guesswork out of setting the fence (photo 15).
And if you’re routing the ends of door rails, even though the stock is technically guided by a miter gauge, the fence and guide bearing is used to control the cutting depth and keep parts consistent (photo 16).