What is the best method to ensure that a hole is drilled perpendicular to the surface?

The use of a drill guide is the most effective method for ensuring that a hole is drilled perpendicular to the surface. A drill guide is specifically designed to keep the drill bit aligned in the correct direction as it penetrates the material. This tool provides a stable, guided path for the drill bit, which minimizes the chance of undesirable angles or misalignment.

While a drill press also provides a high level of precision and can be used to drill holes perpendicular to a surface, it is typically suited for stationary operations and may not be practical for all drilling applications. A level can help to determine if a surface is flat or horizontal, but it does not directly control the angle at which the drill operates when going into the material. A straight edge can provide a reference for alignment but does not offer active guidance in the drilling process, making it less effective than a dedicated drill guide.

Therefore, utilizing a drill guide is the best practice, as it actively assists in maintaining the proper angle during drilling, ensuring the intended perpendicularity to the surface is achieved with greater accuracy.