I commonly use spade bits to bore 1/2-in. to 1-in. holes in wood because they are cheap, readily available and easily sharpened. But in order to make a clean hole in wood, a spade bit has to be sharp. I keep mine tuned up by sharpening them with a round file — the kind used for sharpening chainsaw teeth. As shown in the drawing, I file the inboard cutting edges of the bits to make them curved. This filing leaves a pair of sharp spurs that cleanly slice the wood fibers during a cut.
I have also used a spade bit modified in this manner to bore slightly oversize holes for dowels. I spread the spurs outward a little by using a ball-peen hammer and a vise for an anvil. After the holes have been drilled, I file the bit back to its original diameter.
Roger Niesen, Ellsworth, ME
Edited and Illustrated by Charles Miller
From Fine Homebuilding #42
