What method should be used for keeping the hole on center when drilling in concrete?

Using cross lines is the most effective method for keeping the hole on center when drilling in concrete. This technique involves drawing two intersecting lines that form a cross at the intended drilling point. The intersection serves as a precise reference mark, ensuring that the drill bit is aligned accurately with the desired center point.

By creating a cross with one line extending horizontally and the other vertically, you can easily adjust the drill to align with both axes. This method is particularly useful in concrete, where precision is critical for structural integrity and the successful installation of components. It helps to prevent misalignment often caused by the drill bit wandering off-center, which can occur if only a single line or other methods are used.

Other methods, such as diagonal lines or single lines, may not provide sufficient reference points for maintaining the correct alignment when drilling in hard materials like concrete. Curved lines, in particular, are not practical for precise drilling as they could lead to ambiguity in the center point. Thus, using cross lines stands out as the best practice for achieving accuracy and ensuring long-lasting results in drilling operations.