As spoon bits are made from steel that has not been hardened, it is important to make sure they stay as sharp as possible, as they will blunt quickly in comparison to other types of drill bit.
Fortunately, unhardened steel can easily be sharpened with a file or a slip stone.
It’s most important to keep the leading edge of the bit sharp. Normally, this will be the right hand edge as you look into the hollow of the blade. This is because it will do the majority of the work when boring a hole. However, both edges should be kept sharp so that the bit can be seated (the process of making a small indentation in the wood to keep the bit centred).
Using the tip of a fine file or a fine grain slipstone (tapered sharpening stone), sharpen along the length of the top edge of the blade, following the shallow inner bevel. A few passes with the file or stone should be enough.
Changing the profile of the bit
Some craftsmen prefer the cutting blade of a spoon bit to have even more of an inner bevel, and alter the shape of the inside of their bit to remove what they consider to be excess metal. This should not be necessary for general woodworking projects, but if you decide to give it a go then remember to avoid filing the outside of the bit so as not to lessen its diameter.
