Q: I like to use a pattern bit on my router when making identical parts. One of my tool catalogs lists over 30 of these bits ranging in size from 1/4" to 1-1⁄4" in diameter. I can understand different lengths of bits to accommodate various wood thicknesses, but what’s the advantage of different bit diameters?
A: The plethora of different pattern-bit diameters is more than a marketing ploy. I can think of several practical reasons for owning a variety of them. First, small-diameter bits are sometimes your only solution for sneaking into those tight or tiny areas of a template where a bigger bit just can’t reach. But, they’re no match for making heavy cuts or routing thick workpieces with a long bit. In these situations, larger diameter bits offer more mass and stiffness as well as a lower exit angle of the cutting flutes. Those characteristics help reduce chattering and tearout to produce a smoother cut. Whatever pattern bits you choose, look for a shear or spiral geometry when possible. They’ll give you a slicing, rather than a chiseling, action, and I’ve found that they up my odds for a cleaner cut on splintery woods and end grain.
Image #1: Different sized router bits
Image #1 Original Caption: Pattern bits come in a range of diameters to suit everything from tight-quarters work to heavy stock removal.