Dado cleanout bits are part of a larger family of bits we call pattern bits. These are bits with a bearing on the shank end of the bit. (Bits with a bearing on the tip are referred to as flushtrim bits in the Woodsmith style.)
| Pattern Bit Family Tree |
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It’s worth investing in at least a couple versions of these bits. In addition to their function in following templates, the exposed ends of the cutting flutes allow the bits to stand in for ordinary straight bits.
Here are a few things to keep in mind: Longer cutting lengths allow you to work with thicker stock or create deeper details (mortises). They can also be more likely to vibrate and wobble. Shorter cutting lengths are more stable (usually). This makes them ideal for dadoes and grooves, which are usually relatively shallow.
Larger diameters offer more mass to cut smoother. Smaller diameters sneak into tighter spacers and leave smaller rounded corners for you to square up later (on a hinge mortise). Not all pattern bits allow you to plunge straight into a workpiece. I prefer the plunge-cutting style, since I can make stopped cuts a lot easier.
After that, your work will dictate other sizes and cutting lengths. For example, I have a router finger joint jig, so I have a couple of bits that I purchased in order to work with different thicknesses of parts. You can even find spiral pattern bits that leave super smooth edges.
