When soldering, how should the flame be positioned relative to the tube?

When soldering, positioning the flame perpendicular to the tube is ideal because it allows for even heat distribution across the surface being joined. This method ensures that both the solder and the materials being joined reach the appropriate temperature required for effective melting and adhesion. Using a flame that is too angled or parallel may lead to uneven heating, which can result in cold joints or insufficient solder flow. A perpendicular flame helps maintain control over the heating process, making it easier to achieve a strong and reliable solder joint. This precise application of heat is critical in soldering to ensure a good bond and prevent damage to the components involved.