Spade bits, it seems, are always encountering nails, at least in the kinds of rough drilling chores that renovation work involves. But they are among the easiest of cutting tools to sharpen. Set the tool rest on your bench grinder eight degrees down from horizontal (that is to say, eight degrees past three o'clock, when looking at the end of the grinding wheel).
Position the bit with one of its shoulders flush to the wheel. Before starting the grinder, tighten a stop collar on the shaft of the drill about a sixty-fourth of an inch from the edge of the tool rest. Now, start the machine and grind the edge until the stop collar pre-vents further grinding; turn the bit over, line up the cutting lip on the opposite shoulder, and repeat. The stop collar will assure that the bit is ground symmetrically.
To sharpen the tip or “spur,” swing the bit diagonally to the wheel, and align the cutting edge parallel to the surface of the wheel. Go to the other diagonal to grind the other side.