Round-over bits basics

Perhaps no profile bit sees more woodshop action than the round-over bit. Here are some basics on getting the most from this routing workhorse.

Round edges have benefits

Rounded edges give a project a softer, smoother look. The greater the radius of the round-over, the more pronounced this effect becomes.

Also, rounding an edge makes it more durable because it won't show dents, splinter, or lose its finish as easily as a sharp corner. Like a knife that loses its sharp edge, a rounded corner is more "friendly" to people or objects that come in contact with it.
Match bits to the projects

Woodworking plans often specify that you round over an edge to a specific radius, say ¹⁄₂ ". Or, a plan may ask that you round over the edge with a certain bit, again say a ¹⁄₂ " model. In either case, you need a bit that leaves an edge in the shape of a quarter-round with a ¹⁄₂ " radius showing in the drawing.
Radius determines size designation

Manufacturers classify round-over bits according to the radius they cut. So, a ³⁄₈ " round-over bit cuts a ³⁄₈ " radius, and so forth. To determine the radius of a round-over bit, measure either of the dimensions shown in the drawing.
Set up a round-over bit

After mounting a round-over bit in a router, adjust the bit up or down so the bottom of the concave cutting edge aligns flush with the router base or the surface of the router table. Use a flat block of wood, as shown in the drawing, to check your adjustment.

Before cutting your workpiece, test the cut on scrap stock. If the bit extends too far, it will cut a slight ridge into the workpiece surface, called a fillet. If the bit does not extend far enough, it will cut an incomplete radius.
How to add a fillet

By extending the bit slightly, you can cut a round-over with a fillet like the one shown in the first drawing. Use a rule to set the fillet depth as shown in the second drawing.
Round-over bits cut beads

By changing to a smaller pilot bearing, you can make a round-over bit cut a beaded edge like the one in the drawing.
A bearing change allows for beading

To change bearings, simply loosen the setscrew atop the bearing with a hex wrench, as shown in the drawing . A few bearings cost a lot less than dedicated beading bits!
Bit-buying pointers

You can buy round-over bits with radii ranging from ¹⁄₁₆ " to 1¹⁄₄ ". In the WOOD® magazine shop we make the greatest use of round-over bits with these radii: ¹⁄₁₆ " (for "breaking" edges that need to look crisp and sharp, but feel smooth to the touch), ¹⁄₈ ", ¹⁄₄ ", ³⁄₈ ", and ¹⁄₂ ". We recommend that you purchase round-over bits with ¹⁄₂ " shanks if the bit has a ³⁄₈ " or larger radius.