#1 The Flush-Trim Bit: Curved part duplication, easy mortises and accurate dados

Any router bit with straight cutters and a bearing that matches the diameter of those cutters is called a flush-trim bit. That said, there are dozens of different kinds, each able to empower your router to do marvellous things.

Flush-trims are great because they let your router follow the outline of a curved pattern (sometimes called a ‘template’), automatically impart­ing the shape of that pattern onto your work piece. The most common type of flush-trim bit has a bearing on the end, opposite the shaft. This type is typically used in a table-mounted router, with the height of the bit adjusted so the bear­ing rides on the edge of a pattern as it’s fastened to the top surface of your work piece. Prepare a plywood or hardboard template of the precise shape you want to create, rough-cut your wood about 1/16″ larger than the pattern all around using a jigsaw or band saw, temporar­ily fasten the pattern to the wood with double-sided tape or finishing nails, then run the assembly around the spin­ning flush-trim bit. As the bearing rides on the edge of the pattern, it allows the cutters to trim away only the wood that extends beyond the pattern. You get exact duplication of the pattern on your work piece. It’s a powerful technique.

The only hitch in this good news story has to do with wood grain. As long as your router bit is cutting with the grain, excellent results are virtually guaranteed. But if the curved shape of the wood leads the cutters to cut against the grain, you could get rough results or even chunks of wood torn out of your work piece if you don’t do something about it.

Flipping the work piece/pattern sand­wich upside down, so the template sits underneath the work piece (sliding on the router table top), solves this problem by changing the direction that the wood is fed into the bit. To make this happen, however, you’ve also got to change your flush-trim bit from one with a bearing on the end to one with a bearing on the shaft. And while this is a pretty big hassle, it’s something that can be easily avoided.

Another, much better alternative involves using a flush-trim bit with bear­ings on both tip and shaft. This specialty double-bearing bit makes it easy to rout smoothly and safely along the edges of all curved patterns, flipping back and forth to deal with whatever grain direc­tion is at hand. At worst, you might have to raise and lower the bit slightly, so the bearing continues to ride on the edge of the pattern as it sits on top or bottom, depending on how the wood is oriented during that part of the cutting session.

Another kind of flush-trim bit has the bearing only on the shaft. Although you could use this bit for duplicating parts too, it’s best suited for plunging down into work pieces from above, with the bearing directed by a pattern. You’ll find this kind of bit ideal for making mortises and dados of all sizes.

#2 The Chamfer Bit: Classic edge treatment, small and large

While the chamfer profile might seem ho-hum at first, it’s actually one of the most versatile and enduringly attractive, so don’t overlook it. Unlike many other decorative edge treatments, the subtlety of the chamfer is almost never overpow­ering. Even when you want very crisp lines on a project, a delicate, 1/16″-wide chamfer makes sense. It helps edges resist breaking and wear better than a perfectly square corner, and since it’s cut with a router, it’s more consistent than sanding corners slightly rounded by hand.

At the other end of the size spec­trum, large chamfer bits are one of the best ways to make heavy, outdoor woodwork look great. A honking-big 2 ½” dia. chamfer bit set to mill a ½” or ¾”-wide cham­fer on the edges of a 6×6 or 8×8 makes ordinary, pressure-treated posts look like parts of fine, timber-frame joinery. You can also use this approach to good effect on interior beams and posts, too. For best results, start and stop these cham­fers several inches away from the ends of the beams you’re milling. The transi­tion between routed and unrouted corners looks great.

#3 The Bullnose Bit: Clean, elegant trim and a better fit

In the router bit world, ‘bull­nose’ refers to any bit with a semi-circular, concave pro­file. The most useful versions have a bearing on top, though this bearing isn’t always used. In fact, most of the bullnose work I do happens on a router table, with a fence and feather board supporting strips of wood that I’m making into trim. The bearing is still there, it just sits out of the way, behind the fence.

Bullnose profiles are useful in two major ways: first as stand-alone trim stacked together with other trim elements to produce intricate mouldings, and second as a decora­tive detail routed into the face of adjoining parts or bead board paneling. The real beauty of bullnose in this application is the way it makes the transition between adjoining surfaces less critical. A little bit of mis­match where two cabinet doors meet, for instance, is much less noticeable when the curved edge of a small, bullnose profile is located right along the side of one door stile.

Angled Cutters Mean Smoother Cuts

Slicing wood yields the smooth­est cuts, and that’s why the best performing router bits have cutters that are angled relative to the shaft. Though it doesn’t look like much, this leading-edge cutter geometry results in a slicing action that han­dles contrary wood grain better than router bits that hack away at the wood square-on.

Flush-trim, chamfer and bullnose router bits are certainly not the only ones you’ll need, but they can vault your work to a new level, in ways that are often overlooked.