Which bit should I use for pattern routing?

After seeing photos of template routing, I've begun using this technique for making duplicate project parts. But how do I know whether to use a bit with the bearing on top or a bit with the bearing on the bottom?
—Brian Quick, Morgantown, W. Va.

Both bits work essentially the same, Brian, although they go by different names. A flush-trim bit has a bearing below the cutters, while a pattern bit has a bearing above the cutters. Before using either bit, you first bandsaw the workpiece to rough shape, slightly larger than your template. For trimming to size, we prefer to position the template on top for better visibility, as shown above. Use the pattern bit for handheld routing—remembering to elevate the workpiece to avoid cutting into your workbench. But when trimming edge banding flush with plywood, use a flush-trim bit in a handheld router. For router-table use, go with the flush-trim bit because, when inverted, the bearing sits above the cutters (below), an extra bit of safety.

In most cases, both types of bits have straight cutters. For about a 30–40 percent upcharge, you can buy bits with angled, downshear cutters or solid-carbide spiral bits that reduce tear-out. And, you can buy bits with top and bottom bearings to get the best of both types in a single bit; these sell for about 50 percent more than single-bearing bits.