Pilot hole
From Wikipedia, the free encyclopedia
In construction, a pilot hole is a small hole drilled into a piece of construction material. Its purpose may be:
- to guide a larger drill to the appropriate location and ease the job of the larger drill,
- allow the insertion of another hole-making tool, such as a knockout punch, that will produce the final-sized hole, or
- locate, guide, and provide clearance for a self-threading screw in wood or plastic to prevent damaging the material or breaking the screw.
A pilot hole may be drilled the full extent of the final hole, or may only be a portion of the final depth. The pilot drill may be a standard twist drill, another type of drill bit appropriate for the material, or, when the primary purpose is precisely locating a hole, may be made with a short, stiff center drill.
The pilot hole also reduces the power needed to turn a large drill bit, and reduces the large bit breakage risk. For twist drill bits, the pilot size is usually selected so that the chisel point of the larger drill does not need to remove any material, which reduces the chance of splitting the web of the bit. A pilot thus sized also prevents a larger drill bit from slipping on the material and guides the larger bit effectively. Very large holes may be stepped by drilling successively larger pilot holes before the final size drill is used.[1]
On harder materials, such as most metals and many plastics, and sometimes on softer materials like wood, a center punch is used before drilling the pilot hole to ensure that the smaller pilot drill bit does not slip and that it starts at the correct location.
