Routing Basics – Part 4: Edge Profiling Bits
A decorative edge can add considerable visual appeal to any project. The choices for edge forming bits are almost endless and the bits relatively simple to use; following some straightforward guidelines will guarantee success even for a first time user.
When most woodworkers first pick up a router, chances are it will be to profile an edge, whether for a table leg, drawer front, tabletop or cabinetry. Using edge-profiling bits can be the least intimidating way to learn how to use this versatile tool. Like most router bits, edging bits can be used freehand or on a router table. Remember that large bits shouldn’t be used freehand. Fortunately manufacturers will always stipulate which bits should be used in a router table and the top speed the bit should not exceed; it is in your interest to follow their advice. When you are routing small pieces of stock it also makes good sense to use a router table, push blocks, and feather boards, regardless of the size of the bit.
Bit guided by ball bearing guides
Lining up bearing with router fence (photo shows double exposure)
Basic edge profiling shapes
Complex edge profiles
Primary Edge Profiles
Almost every trim profile can be reduced to one of five basic shapes: chamfer, cove, round, bead and flute. (Note: The word ‘flute’ is also used to refer to the cutting edge of a router bit). These are the basic shapes that have defined various furniture styles throughout history. Originally these profiles were scraped or cut into the wood using sharpened metal blades. The blades were shaped with a negative of the desired profile by means of scratch sticks or beading tools, and then more elaborate hand planes. Industrial shaping of wood has been done using machines for well over a hundred and thirty years, but it wasn’t until the portable router became widely available in the 1970’s that the hobbyist woodworker had access to such powerful edge shaping capability.
These five basic shapes will see you through most of your woodworking needs. Builders of Arts & Crafts style furniture will find the chamfer bit the most useful of this group while those that build pine country style furniture would be best served with a selection of round over and cove bits. Beads and flutes are used to add decorative detail to many different furniture and architectural styles. Single bead and flute bits are also used to make the planking for strip built canoes.
You are, of course, not limited to these five basic shapes. Manufacturers combine these shapes to produce hundreds of complex edge designs, with just about every possible profile that you can imagine. You can use the five basic edge-forming bits in combination to create a multitude of edge treatment possibilities. For example, combine a cove and a round over to rout a Roman Ogee or a bead and cove to rout a Classical Bead and Cove. However, in most cases you will find it easier to simply purchase a complex edge bit to suit your particular need. You can also purchase a ‘multi-profile’ bit, which enables you to rout dozens of different profiles from a single bit. You simply adjust the height of the bit to use the portion of the profile you need.
As with all tooling, better quality bits cost considerably more than the hobbyist starter sets many outlets sell at discount prices. These low priced starter sets are a great place to begin a collection though. Obtain a starter set when you purchase a router and then, as your experience with the machine grows, replace the bits that you find yourself using most often with higher quality professional bits.
Guiding the Bits
Edge profile bits must be accurately guided along the edge of the work piece for a controlled cut. You will find that a lot of edge-forming bits have a ball bearing guide mounted on the top of the bit (often referred to as piloted bits). These guides act as a fence as the bit rolls along the non-routed portion of the edge. This will only work when there is enough of a ledge for the ball bearing guide to ride on. When the entire edge of the piece is to be profiled then this edge will not be present and the bit cannot be guided by the bearing; these pieces will have to be routed using an external fence on the router base, or with a fence on the router table. As a general rule, when buying a router bit that is available with or without a guide bearing, choose the one that has a bearing.
When using a router bit in a router table, a ball bearing guide, a fence, or both, can guide the work. Using a two-part fence with sacrificial faces will allow you to close up the opening around the bit resulting in far greater effectiveness with dust control, an important consideration as any errant shavings or sawdust that comes between the work and the bearing or fence will affect the final cut. To use a ball bearing bit with a fence, use a steel ruler to ensure the bearing and fence are perfectly lined up. Having the bearing recessed slightly behind the fence will not affect the cut but having the bearing set proud of the fence will result in snipe similar to what you would see from a jointer.
The Possibilities Are Endless
Profiling an edge is all about adding visual detail to your project, and those details are created using light and shadow. Arts & Crafts furniture is very rectilinear and fancy curved profiles would seem completely out of place. Using a chamfer on edges results in finely defined visual lines as the two crisp edges that define the chamfer catch the light. On a more casual piece of furniture a round over provides a less distinct transition from one surface to the adjacent surface as there are no sharp edges to catch the light and the light changes gradually as it is reflected around the curve. To create a slightly more defined look, raise the bit a little higher to cut a fillet at the same time. This creates a sharp edge to catch the light. Use a cove to lighten the look of a thicker top by removing some of the material from the underside.
Now you’re ready to dress up any edge on your next project.
Five tips for successful edge routing
This series continues here.